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• How to designing a generic databse whos layout may change over time?

  - by mawg

  Here's a tricky one - how do I programatically create and interrogate a database who's contents I can't really foresee? I am implementing a generic input form system. The user can create PHP forms with a WYSIWYG layout and use them for any purpose he wishes. He can also query the input. So, we have three stages: a form is designed and generated. This is a one-off procedure, although the form can be edited later. This designs the database. someone or several people make use of the form - say for daily sales reports, stock keeping, payroll, etc. Their input to the forms is written to the database. others, maybe management, can query the database and generate reports. Since these forms are generic, I can't predict the database structure - other than to say that it will reflect HTML form fields and consist of a the data input from collection of edit boxes, memos, radio buttons and the like. Questions and remarks: A) how can I best structure the database, in terms of tables and columns? What about primary keys? My first thought was to use the control name to identify each column, then I realized that the user can edit the form and rename, so that maybe "name" becomes "employee" or "wages" becomes ":salary". I am leaning towards a unique number for each. B) how best to key the rows? I was thinking of a timestamp to allow me to query and a column for the row Id from A) C) I have to handle column rename/insert/delete. Foe deletion, I am unsure whether to delete the data from the database. Even if the user is not inputting it from the form any more he may wish to query what was previously entered. Or there may be some legal requirements to retain the data. Any gotchas in column rename/insert/delete? D) For the querying, I can have my PHP interrogate the database to get column names and generate a form with a list where each entry has a database column name, a checkbox to say if it should be used in the query and, based on column type, some selection criteria. That ought to be enough to build searches like "position = 'senior salesman' and salary 50k". E) I probably have to generate some fancy charts - graphs, histograms, pie charts, etc for query results of numerical data over time. I need to find some good FOSS PHP for this. F) What else have I forgotten? This all seems very tricky to me, but I am database n00b - maybe it is simple to you gurus?

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• How do you make a Custom Data Generator for SQL XML DataType.

  - by Keith Sirmons

  Howdy, I am using Visual Studio 2010 and am playing around with the Database Projects. I am creating a DataGenerationPlan to insert data into a simple table, in which one of the column datatypes is XML. Out of the box, the generation plan uses the Regular Expression generator and generates something like this : HGcSv9wa7yM44T9x5oFT4pmBkEmv62lJ7OyAmCnL6yqXC2X.......... I am looking at creating a custom data Generator for this data type and have followed this site for the basics: http://msdn.microsoft.com/en-us/library/aa833244.aspx This example works if I am creating a string datatype and using it for a nvarchar datatype. What do I need to change to hook this Generator to the XML Datatype? Below are my code files. The string property works for nvarchar. The XElement property does not work for the xml datatype, and the RecordXMLDataGenerator is not listed as an option in the Generator column for the generation plan. CustomDataGenerators: using System; using System.Collections.Generic; using System.Linq; using System.Text; using Microsoft.Data.Schema.Tools.DataGenerator; using Microsoft.Data.Schema.Extensibility; using Microsoft.Data.Schema; using Microsoft.Data.Schema.Sql; using System.Xml.Linq; namespace CustomDataGenerators { [DatabaseSchemaProviderCompatibility(typeof(SqlDatabaseSchemaProvider))] public class RecordXMLDataGenerator : Generator { private XElement _RecordData; [Output(Description = "Generates string of XML Data for the Record.", Name = "RecordDataString")] public string RecordDataString { get { return _RecordData.ToString(SaveOptions.None); } } [Output(Description = "Generates XML Data for the Record.", Name = "RecordData")] public XElement RecordData { get { return _RecordData; } } protected override void OnGenerateNextValues() { base.OnGenerateNextValues(); XElement element = new XElement("Root", new XElement("Children1", 1), new XElement("Children6", 6) ); _RecordData = element; } } } XML Extensions File: <?xml version="1.0" encoding="utf-8" ?> <extensions assembly="" version="1" xmlns="urn:Microsoft.Data.Schema.Extensions" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="urn:Microsoft.Data.Schema.Extensions Microsoft.Data.Schema.Extensions.xsd"> <extension type="CustomDataGenerators.RecordXMLDataGenerator" assembly="CustomDataGenerators, Version=1.0.0.0, Culture=neutral, PublicKeyToken=xxxxxxxxxxxx" enabled="true"/> </extensions> Table.sql: CREATE TABLE [dbo].[Record] ( id int IDENTITY (1,1) NOT NULL, recordData xml NULL, userId int NULL, test nvarchar(max) NULL, rowver rowversion NULL, CONSTRAINT pk_RecordID PRIMARY KEY (id) )

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• Problems with contenteditable in Firefox

  - by Jonathan

  Hello, I am working on a Javascript WYSIWYG editor in Firefox. I am using a div with the contenteditable attribute set to true in order to accomplish this (I cannot use a contenteditable iframe for this particular project). This contenteditable div is nested in another div that is not contenteditable. I am encountering the following two problems when using execCommand to apply formatting, including font style and size, as well as bold, italic, and underline: When all text in the div is selected, execCommand simply does not work. execCommand works fine when only part of the text is selected, but does nothing when all of the text is selected. Applying formatting with no text selected yields unexpected results. For example, when calling execCommand('bold') with no text selected and then typing results in bold text being typed until a spacebar is inserted, at which point the bold formatting is lost (until another space is inserted, interestingly enough; then the text becomes bold again). To see what I mean, please try running the following HTML code in Firefox 3: <html> <head><title></title></head> <body> <button onClick="execCommand('bold', false, null);">Bold</button> <div style="width: 300px; border: 1px solid #000000;"> <div contenteditable="true">Some editable text</div> </div> </body> </html> Please try the following: Select the word "Some" only. Click the Bold button. This will make the text bold, as expected. Select the entire phrase "Some editable text" (either manually or using CTRL-A). Click the Bold button. Nothing happens. This demonstrates the first bug shown above. Hit the backspace key to clear the div. Click the Bold button and begin typing. Type a few words with spaces. This will demonstrate the second bug. Any ideas on what could be causing these problems and how to work around them would be greatly appreciated!

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• Any way to speed up this hierarchical query?

  - by RenderIn

  I've got a serious performance problem with a hierarchical query that I can't seem to fix. I am modeling several organization charts in my database, each representing a virtual organization within our company. For example, we have several temporary committees that are created from time to time and there may be a Committee Organizer role at the top of this virtual hierarchy, with several people assigned to the Committee Member role beneath the organizer. Some of our virtual organizations have many levels and several branches at each level. I have a single table in which I represent all the role assignments. i.e. a ROLE_ID column and a PARENT_ROLE_ID column which is a foreign key to the ROLE_ID column. For each assignment we also store as a column the location in the company where this person has the assignment. For example, the Committee Organizer would have a company-level/ CEO assignment, while the committee members would have department-level assignments such as ACCOUNTING, MARKETING, etc. So to model the organizer/member relationship for two individuals we would have: ROLE_ID = 4 PARENT_ROLE_ID = NULL EMPLOYEE_NUMBER = 213423 COMPANY_LOCATION = CEO ROLE_ID = 5 PARENT_ROLE_ID = 4 EMPLOYEE_NUMBER = 838221 COMPANY_LOCATION = ACCOUNTING Here's where things get tricky. I have an application that every person in the organization can log in to. When they log in they should be able to view all the virtual organizations in our company. e.g. the committee members should be able to see the committee organizer and vice-versa. However, only the committee organizer should be able to edit the committee members. The difficulty is in determining whether an individual (who can have multiple role assignments) has edit access for each other assignment. While this seems simple in the example, consider a virtual organization in which we have President at the top, 5 departments directly beneath him, 2 subdepartments below each department. We only want people in the Accounting department to be able to edit individuals in the subdepartments belonging to the Accounting department. They should not have edit access to anybody in the Marketing department or its subdepartments. To determine edit access when a user views a virtual organization in our company I run a query that executes two inline views: A) Hierarchically query for all assignments in this virtual organization and using SYS_CONNECT_BY_PATH to store the entire path to each user/role/company_location and B) Hierarchically retrieve all the assignments the individual logged in has and using the SYS_CONNECT_BY_PATH to store the entire path to each of these assignments. The result of the query is all the records from A) plus a boolean determined by joining with B) which flags whether the logged in user has edit access for each record. Indexes don't seem to be helping... it simply appears that there is too much processing going on to separate all the records and then determine edit access. One issue is that I can't store the SYS_CONNECT_BY_PATH and index it... determining whether an individual record has edit access consists of comparing if: test_record_sys_path LIKE individual_record_sys_path || '%' Is a materialized view the answer?

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• Optimizing spacing of mesh containing a given set of points

  - by Feynman

  I tried to summarize the this as best as possible in the title. I am writing an initial value problem solver in the most general way possible. I start with an arbitrary number of initial values at arbitrary locations (inside a boundary.) The first part of my program creates a mesh/grid (I am not sure which is the correct nuance), with N points total, that contains all the initial values. My goal is to optimize the mesh such that the spacing is as uniform as possible. My solver seems to work half decently (it needs some more obscure debugging that is not relevant here.) I am starting with one dimension. I intend to generalize the algorithm to an arbitrary number of dimensions once I get it working consistently. I am writing my code in fortran, but feel free to reply with pseudocode or the language of your choice. Allow me to elaborate with an example: Say I am working on a closed interval [1,10] xmin=1 xmax=10 Say I have 3 initial points: xmin, 5 and xmax num_ivc=3 known(num_ivc)=[xmin,5,xmax] //my arrays start at 1. Assume "known" starts sorted I store my mesh/grid points in an array called coord. Say I want 10 points total in my mesh/grid. N=10 coord(10) Remember, all this is arbitrary--except the variable names of course. The algorithm should set coord to {1,2,3,4,5,6,7,8,9,10} Now for a less trivial example: num_ivc=3 known(num_ivc)=[xmin,5.5,xmax or just num_ivc=1 known(num_ivc)=[5.5] Now, would you have 5 evenly spaced points on the interval [1, 5.5] and 5 evenly spaced points on the interval (5.5, 10]? But there is more space between 1 and 5.5 than between 5.5 and 10. So would you have 6 points on [1, 5.5] followed by 4 on (5.5 to 10]. The key is to minimize the difference in spacing. I have been working on this for 2 days straight and I can assure you it is a lot trickier than it sounds. I have written code that only works if N is large only works if N is small only works if it the known points are close together only works if it the known points are far apart only works if at least one of the known points is near a boundary only works if none of the known points are near a boundary So as you can see, I have coded the gamut of almost-solutions. I cannot figure out a way to get it to perform equally well in all possible scenarios (that is, create the optimum spacing.)

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• CakePHP HABTM: Editing one item casuses HABTM row to get recreated, destroys extra data

  - by leo-the-manic

  I'm having trouble with my HABTM relationship in CakePHP. I have two models like so: Department HABTM Location. One large company has many buildings, and each building provides a limited number of services. Each building also has its own webpage, so in addition to the HABTM relationship itself, each HABTM row also has a url field where the user can visit to find additional information about the service they're interested and how it operates at the building they're interested in. I've set up the models like so: <?php class Location extends AppModel { var $name = 'Location'; var $hasAndBelongsToMany = array( 'Department' => array( 'with' => 'DepartmentsLocation', 'unique' => true ) ); } ?> <?php class Department extends AppModel { var $name = 'Department'; var $hasAndBelongsToMany = array( 'Location' => array( 'with' => 'DepartmentsLocation', 'unique' => true ) ); } ?> <?php class DepartmentsLocation extends AppModel { var $name = 'DepartmentsLocation'; var $belongsTo = array( 'Department', 'Location' ); // I'm pretty sure this method is unrelated. It's not being called when this error // occurs. Its purpose is to prevent having two HABTM rows with the same location // and department. function beforeSave() { // kill any existing rows with same associations $this->log(__FILE__ . ": killing existing HABTM rows", LOG_DEBUG); $result = $this->find('all', array("conditions" => array("location_id" => $this->data['DepartmentsLocation']['location_id'], "department_id" => $this->data['DepartmentsLocation']['department_id']))); foreach($result as $row) { $this->delete($row['DepartmentsLocation']['id']); } return true; } } ?> The controllers are completely uninteresting. The problem: If I edit the name of a Location, all of the DepartmentsLocations that were linked to that Location are re-created with empty URLs. Since the models specify that unique is true, this also causes all of the newer rows to overwrite the older rows, which essentially destroys all of the URLs. I would like to know two things: Can I stop this? If so, how? And, on a less technical and more whiney note: Why does this even happen? It seems bizarre to me that editing a field through Cake should cause so much trouble, when I can easily go through phpMyAdmin, edit the Location name there, and get exactly the result I would expect. Why does CakePHP touch the HABTM data when I'm just editing a field on a row? It's not even a foreign key!

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• Rails Google Maps integration Javascript problem

  - by JZ

  I'm working on Rails 3.0.0.beta2, following Advanced Rails Recipes "Recipe #32, Mark locations on a Google Map" and I hit a road block: I do not see a google map. My @adds view uses @adds.to_json to connect the google maps api with my model. My database contains "latitude" "longitude", as floating points. And the entire project can be accessed at github. Can you see where I'm not connecting the to_json output with the javascript correctly? Can you see other glairing errors in my javascript? Thanks in advance! My application.js file: function initialize() { if (GBrowserIsCompatible() && typeof adds != 'undefined') { var map = new GMap2(document.getElementById("map")); map.setCenter(new GLatLng(37.4419, -122.1419), 13); map.addControl(new GLargeMapControl()); function createMarker(latlng, add) { var marker = new GMarker(latlng); var html="<strong>"+add.first_name+"</strong><br />"+add.address; GEvent.addListener(marker,"click", function() { map.openInfoWindowHtml(latlng, html); }); return marker; } var bounds = new GLatLngBounds; for (var i = 0; i < adds.length; i++) { var latlng=new GLatLng(adds[i].latitude,adds[i].longitude) bounds.extend(latlng); map.addOverlay(createMarker(latlng, adds[i])); } map.setCenter(bounds.getCenter(),map.getBoundsZoomLevel(bounds)); } } window.onload=initialize; window.onunload=GUnload; Layouts/adds.html.erb: <script src="http://maps.google.com/maps?file=api&amp;v=2&amp;sensor=true_or_false&amp;key=ABQIAAAAeH4ThRuftWNHlwYdvcK1QBTJQa0g3IQ9GZqIMmInSLzwtGDKaBQvZChl_y5OHf0juslJRNx7TbxK3Q" type="text/javascript"></script> <% if @adds -%> <script type="text/javascript"> var maps = <%= @adds.to_json %>; </script> <% end -%>

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• WPF - ListBox ignores Style When ItemsSource is bound

  - by Andy T

  Hi, I have created styled a ListBox in WPF so that it is rendered as a checkbox list. When I populate the ListBox's items manually, the styling works perfectly. However, when I instead bind the ItemsSource of the ListBox to a static resource (an ItemsControl containing the required items), the styling is completely dropped. Here's the style: <Style x:Key="CheckBoxListStyle" TargetType="ListBox"> <Style.Resources> <Style TargetType="ListBoxItem"> <Setter Property="Template"> <Setter.Value> <ControlTemplate TargetType="ListBoxItem"> <Grid Margin="2"> <Grid.ColumnDefinitions> <ColumnDefinition Width="Auto" /> <ColumnDefinition /> </Grid.ColumnDefinitions> <CheckBox IsChecked="{Binding IsSelected, RelativeSource={RelativeSource TemplatedParent}, Mode=TwoWay}"/> <ContentPresenter Grid.Column="1" Margin="2,0,0,0" /> </Grid> </ControlTemplate> </Setter.Value> </Setter> </Style> </Style.Resources> <Setter Property="ItemsPanel"> <Setter.Value> <ItemsPanelTemplate> <WrapPanel Orientation="Vertical" /> </ItemsPanelTemplate> </Setter.Value> </Setter> <Setter Property="BorderThickness" Value="0" /> <Setter Property="Background" Value="Transparent" /> </Style> Here's the code for the ListBox that shows the style correctly: <ListBox x:Name="ColumnsList" Grid.Column="0" Grid.Row="0" Style="{StaticResource CheckBoxListStyle}" BorderThickness="1"> <ListBox.Items> <ListBoxItem>Test</ListBoxItem> <ListBoxItem>Test2</ListBoxItem> <ListBoxItem>Test3</ListBoxItem> </ListBox.Items> </ListBox> Here's the code for the ListBox that ignores the style: <ListBox x:Name="ColumnsList2" Grid.Column="0" Grid.Row="0" Style="{StaticResource CheckBoxListStyle}" BorderThickness="1" ItemsSource="{Binding Source={StaticResource Test1}, Path=Items}"> </ListBox> Hoping someone can help - I'm pretty new to all this and have tried everything I can think of, but everything I've read leads me to believe that setting ItemsSource should have the same outcome as setting the items manually, so I can't see any reason why this would not work. Thanks, AT

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• Complex Entity Framework linked-graphs issue: how to limit change set / break the graph?

  - by Hightechrider

  I have an EDMX containing Sentences, and Words, say and a Sentence contains three Words, say. Appropriate FK relationships exist between the tables. I create some words: Word word1 = new Word(); Word word2 = ... I build a Sentence: Sentence x = new Sentence (word1, word2, word3); I build another Sentence: Sentence y = new Sentence (word1, word4, word5); I try to save x to the database, but EF builds a change set that includes everything, including y, word4 and word5 that aren't ready to save to the database. When SaveChanges() happens it throws an exception: Unable to determine the principal end of the ... relationship. Multiple added entities may have the same primary key. I think it does this because Word has an EntityCollection<Sentence> on it from the FK relationship between the two tables, and thus Sentence y is inextricably linked to Sentence x through word1. So I remove the Navigation Property Sentences from Word and try again. It still tries to put the entire graph into the change set. What suggestions do the Entity Framework experts have for ways to break this connection. Essentially what I want is a one-way mapping from Sentence to Word; I don't want an EntityCollection<Sentence> on Word and I don't want the object graph to get intertwined like this. Code sample: This puts two sentences into the database because Verb1 links them and EF explores the entire graph of existing objects and added objects when you do Add/SaveChanges. Word subject1 = new Word(){ Text = "Subject1"}; Word subject2 = new Word(){ Text = "Subject2"}; Word verb1 = new Word(){ Text = "Verb11"}; Word object1 = new Word(){ Text = "Object1"}; Word object2 = new Word(){ Text = "Object2"}; Sentence s1 = new Sentence(){Subject = subject1, Verb=verb1, Object=object1}; Sentence s2 = new Sentence(){Subject=subject2, Verb=verb1, Object=object2}; context.AddToSentences(s1); context.SaveChanges(); foreach (var s in context.Sentences) { Console.WriteLine(s.Subject + " " + s.Verb + " " + s.Object); }

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• Display multiple new windows

  - by Ricardo Deano

  Afternoon all. I have the following scenario: I have a search page where by a client searches for a product from a drop down list, upon clicking a button, a gridview is produced display the spec. What I would like is the functionality for the user to make their selection and a new window pops up with the spec. So I have a simple code behind for the search page: protected void Button1_Click(object sender, EventArgs e) { Session["Product"] = DropDownList1.SelectedValue; string strScript = "window.open('GridViewPage.aspx', 'Key', 'height=500,width=800,toolbar=no,menubar=no,scrollbars=yes,resizable=yes,titlebar=no');"; ScriptManager.RegisterStartupScript(this, typeof(string), "", strScript, true); } And a gridviewpage that presents the data based upon the session created in the search page: <asp:GridView ID="GridView2" runat="server" AutoGenerateColumns="False" DataSourceID="LinqDataSource1"> <Columns> <asp:BoundField DataField="Product" HeaderText="MemberID" SortExpression="MemberID" /> <asp:BoundField DataField="Spec" HeaderText="Spec" SortExpression="Spec" /> </Columns> </asp:GridView> <asp:LinqDataSource ID="LinqDataSource1" runat="server" ContextTypeName="GridViewInNewWindow.ProductDataContext" EntityTypeName="" TableName="tblProducts" Where="Product == @Product"> <WhereParameters> <asp:SessionParameter Name="Product" SessionField="Product" Type="String" /> </WhereParameters> </asp:LinqDataSource> Now upon first iteration, this does the job...gridview presented in new window...hurrah! i.e. a user searches for egg, the spec for an egg is presented in a new window. However, what I would like to happen is that the user can make multiple searches so a number of new windows are opened. i.e. a user searches for egg once, the spec is returned in a new window; they then wish to see the spec for a chicken, so they use the search page to find said chicken, click the button and another new window is shown displaying the chicken's specs. Does anyone know how I can achieve this? Apologies if this is simple stuff, I am just finding my feet.

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• One click to trigger several search forms?

  - by Christian

  Hello, I have 1 main search form with a submit button and several secondary search forms with submit buttons. What I would like to do is when I enter text and click on the submit button of the main search form, the same text gets copied in all of the secondary search forms and all the submit buttons of the secondary search forms get automatically hit. The HTML code for the mains earch form is shown below: <form action="query.php" method="get"> Search: <input type="text" name="item" size="30"> <input type="submit" value="send"> </form> One of the several secondary search forms is shown below: <FORM action="http://www.dpbolvw.net/interactive" method="GET" target="_blank"> <div style="float: left; padding: 0 3px 0 0;"> <INPUT type="text" name="src" size="9" value="<?php $input = $_GET['item']; echo $input;?>" style="width: 110px; height: 22px;margin:0; padding: 0; font-size:140%;"> </div> <div style="float: left; padding: 0 3px 0 0;"> <input type="image" name="submit" value="GO" src="http://images.guitarcenter.com/Content/GC/banner/go.gif" alt="Search" style="font-size:140%"> /div> <input type="hidden" name="aid" value="1234"/> <input type="hidden" name="pid" value="1234"/> <input type="hidden" name="url" value="http://www.guitarcenter.com/Search/Default.aspx"/> </form> Notice the php code that I put in the "value" field of the secondary search form: <?php $input = $_GET['item']; echo $input;?> This automatically copies the text that I entered in the main search form into the secondary search form. I thus figured out how to do that. The problem is to "simulate" an "Enter" keystroke or a click on the "GO" button with the mouse on the secondary search form when the user hits the Enter key or hits the "SEND" button with the mouse on the main search form. Thank you for your insight!

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• Rails / ActiveRecord Modeling Help

  - by JM

  I’m trying to model a relationship in ActiveRecord and I think it’s a little beyond my skill level. Here’s the background. This is a horse racing project and I’m trying to model a horses Connections over time. Connections are defined as the Horse’s Current: Owner, Trainer and Jockey. Over time, a horse’s connections can change for a lot of different reasons: The owner sells the horse in a private sale The horse is claimed (purchase in a public sale) The Trainer switches jockeys The owner switches trainers In my first attempt at modeling this, I created the following tables: Horses, Owners, Trainers, Jockeys and Connections. Essentially, the Connections table was the has-many-through join table and was structured as follows: Connections Table 1 Id Horse_id Owner_id Trainer_id Jockey_id Status_Code Status_Date Change_Code The Horse, Owner, Trainer and Jockey foreign keys are self explanatory. The status code is 1 or 0 (1 active, 0 inactive) and the status date is the date the status changed. Change_code is and integer or string value that represent the reason for the change (private sale, claim, jockey change, etc) The key benefit of this approach is that the Connection is represented as one record in the connections table. The downside is that I have to have a table for Owner (1), Trainer (2) and Jockey (3) when one table could due. In my second attempt at modeling this I created the following tables: Horses, Connections, Entities The Entities tables has the following structure Entities Table id First_name Last_name Role where Role represents if the entity is a Owner, Trainer or Jockey. Under this approach, my Connections table has the following structure Connections Table 2 id Horse_id Entity_id Role Status_Code Status_Date Change_Code 1 1 1 1 1 1/1/2010 2 1 4 2 1 1/1/2010 3 1 10 3 1 1/1/2010 This approach has the benefit of eliminating two tables, but on the other hand the Connection is now comprised of three different records as opposed to one in the first approach. What believe I’m looking for is an approach that allows me to capture the Connection in one record, but also uses an Entities table with roles instead of the Owner, Trainer and Jockey tables. I’m new to ActiveRecord and rails so any and all input would be greatly appreciated. Perhaps there are other ways that would even be better. Thanks!

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• How do I add a column that displays the number of distinct rows to this query?

  - by Fake Code Monkey Rashid

  Hello good people! I don't know how to ask my question clearly so I'll just show you the money. To start with, here's a sample table: CREATE TABLE sandbox ( id integer NOT NULL, callsign text NOT NULL, this text NOT NULL, that text NOT NULL, "timestamp" timestamp with time zone DEFAULT now() NOT NULL ); CREATE SEQUENCE sandbox_id_seq START WITH 1 INCREMENT BY 1 NO MINVALUE NO MAXVALUE CACHE 1; ALTER SEQUENCE sandbox_id_seq OWNED BY sandbox.id; SELECT pg_catalog.setval('sandbox_id_seq', 14, true); ALTER TABLE sandbox ALTER COLUMN id SET DEFAULT nextval('sandbox_id_seq'::regclass); INSERT INTO sandbox VALUES (1, 'alpha', 'foo', 'qux', '2010-12-29 16:51:09.897579+00'); INSERT INTO sandbox VALUES (2, 'alpha', 'foo', 'qux', '2010-12-29 16:51:36.108867+00'); INSERT INTO sandbox VALUES (3, 'bravo', 'bar', 'quxx', '2010-12-29 16:52:36.370507+00'); INSERT INTO sandbox VALUES (4, 'bravo', 'foo', 'quxx', '2010-12-29 16:52:47.584663+00'); INSERT INTO sandbox VALUES (5, 'charlie', 'foo', 'corge', '2010-12-29 16:53:00.742356+00'); INSERT INTO sandbox VALUES (6, 'delta', 'foo', 'qux', '2010-12-29 16:53:10.884721+00'); INSERT INTO sandbox VALUES (7, 'alpha', 'foo', 'corge', '2010-12-29 16:53:21.242904+00'); INSERT INTO sandbox VALUES (8, 'alpha', 'bar', 'corge', '2010-12-29 16:54:33.318907+00'); INSERT INTO sandbox VALUES (9, 'alpha', 'baz', 'quxx', '2010-12-29 16:54:38.727095+00'); INSERT INTO sandbox VALUES (10, 'alpha', 'bar', 'qux', '2010-12-29 16:54:46.237294+00'); INSERT INTO sandbox VALUES (11, 'alpha', 'baz', 'qux', '2010-12-29 16:54:53.891606+00'); INSERT INTO sandbox VALUES (12, 'alpha', 'baz', 'corge', '2010-12-29 16:55:39.596076+00'); INSERT INTO sandbox VALUES (13, 'alpha', 'baz', 'corge', '2010-12-29 16:55:44.834019+00'); INSERT INTO sandbox VALUES (14, 'alpha', 'foo', 'qux', '2010-12-29 16:55:52.848792+00'); ALTER TABLE ONLY sandbox ADD CONSTRAINT sandbox_pkey PRIMARY KEY (id); Here's the current SQL query I have: SELECT * FROM ( SELECT DISTINCT ON (this, that) id, this, that, timestamp FROM sandbox WHERE callsign = 'alpha' AND CAST(timestamp AS date) = '2010-12-29' ) playground ORDER BY timestamp DESC This is the result it gives me: id this that timestamp ----------------------------------------------------- 14 foo qux 2010-12-29 16:55:52.848792+00 13 baz corge 2010-12-29 16:55:44.834019+00 11 baz qux 2010-12-29 16:54:53.891606+00 10 bar qux 2010-12-29 16:54:46.237294+00 9 baz quxx 2010-12-29 16:54:38.727095+00 8 bar corge 2010-12-29 16:54:33.318907+00 7 foo corge 2010-12-29 16:53:21.242904+00 This is what I want to see: id this that timestamp count ------------------------------------------------------------- 14 foo qux 2010-12-29 16:55:52.848792+00 3 13 baz corge 2010-12-29 16:55:44.834019+00 2 11 baz qux 2010-12-29 16:54:53.891606+00 1 10 bar qux 2010-12-29 16:54:46.237294+00 1 9 baz quxx 2010-12-29 16:54:38.727095+00 1 8 bar corge 2010-12-29 16:54:33.318907+00 1 7 foo corge 2010-12-29 16:53:21.242904+00 1 EDIT: I'm using PostgreSQL 9.0.* (if that helps any).

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• Constructor Injection and when to use a Service Locator

  - by Simon

  I'm struggling to understand parts of StructureMap's usage. In particular, in the documentation a statement is made regarding a common anti-pattern, the use of StructureMap as a Service Locator only instead of constructor injection (code samples straight from Structuremap documentation): public ShippingScreenPresenter() { _service = ObjectFactory.GetInstance<IShippingService>(); _repository = ObjectFactory.GetInstance<IRepository>(); } instead of: public ShippingScreenPresenter(IShippingService service, IRepository repository) { _service = service; _repository = repository; } This is fine for a very short object graph, but when dealing with objects many levels deep, does this imply that you should pass down all the dependencies required by the deeper objects right from the top? Surely this breaks encapsulation and exposes too much information about the implementation of deeper objects. Let's say I'm using the Active Record pattern, so my record needs access to a data repository to be able to save and load itself. If this record is loaded inside an object, does that object call ObjectFactory.CreateInstance() and pass it into the active record's constructor? What if that object is inside another object. Does it take the IRepository in as its own parameter from further up? That would expose to the parent object the fact that we're access the data repository at this point, something the outer object probably shouldn't know. public class OuterClass { public OuterClass(IRepository repository) { // Why should I know that ThingThatNeedsRecord needs a repository? // that smells like exposed implementation to me, especially since // ThingThatNeedsRecord doesn't use the repo itself, but passes it // to the record. // Also where do I create repository? Have to instantiate it somewhere // up the chain of objects ThingThatNeedsRecord thing = new ThingThatNeedsRecord(repository); thing.GetAnswer("question"); } } public class ThingThatNeedsRecord { public ThingThatNeedsRecord(IRepository repository) { this.repository = repository; } public string GetAnswer(string someParam) { // create activeRecord(s) and process, returning some result // part of which contains: ActiveRecord record = new ActiveRecord(repository, key); } private IRepository repository; } public class ActiveRecord { public ActiveRecord(IRepository repository) { this.repository = repository; } public ActiveRecord(IRepository repository, int primaryKey); { this.repositry = repository; Load(primaryKey); } public void Save(); private void Load(int primaryKey) { this.primaryKey = primaryKey; // access the database via the repository and set someData } private IRepository repository; private int primaryKey; private string someData; } Any thoughts would be appreciated. Simon

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• c++ class member functions selected by traits

  - by Jive Dadson

  I am reluctant to say I can't figure this out, but I can't figure this out. I've googled and searched stackoverflow, and come up empty. The abstract, and possibly overly vague form of the question is, how can I use the traits-pattern to instantiate non-virtual member functions? The question came up while modernizing a set of multivariate function optimizers that I wrote more than 10 years ago. The optimizers all operate by selecting a straight-line path through the parameter space away from the current best point (the "update"), then finding a better point on that line (the "line search"), then testing for the "done" condition, and if not done, iterating. There are different methods for doing the update, the line-search, and conceivably for the done test, and other things. Mix and match. Different update formulae require different state-variable data. For example, the LMQN update requires a vector, and the BFGS update requires a matrix. If evaluating gradients is cheap, the line-search should do so. If not, it should use function evaluations only. Some methods require more accurate line-searches than others. Those are just some examples. The original version instatiates several of the combinations by means of virtual functions. Some traits are selected by setting mode bits. Yuck. It would be trivial to define the traits with #define's and the member functions with #ifdef's and macros. But that's so twenty years ago. It bugs me that I cannot figure out a whiz-bang modern way. If there were only one trait that varied, I could use the curiously recurring template pattern. But I see no way to extend that to arbitrary combinations of traits. I tried doing it using boost::enable_if, etc.. The specialized state info was easy. I managed to get the functions done, but only by resorting to non-friend external functions that have the this-pointer as a parameter. I never even figured out how to make the functions friends, much less member functions. Perhaps tag-dispatch is the key. I haven't gotten very deeply into that. Surely it's possible, right? If so, what is best practice?

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• How build my own Application Setting

  - by adisembiring

  I want to build a ApplicationSetting for my application. The ApplicationSetting can be stored in a properties file or in a database table. The settings are stored in key-value pairs. E.g. ftp.host = blade ftp.username = dummy ftp.pass = pass content.row_pagination = 20 content.title = How to train your dragon. I have designed it as follows: Application settings reader: interface IApplicationSettingReader { read(); } DatabaseApplicationSettingReader { dao appSettingDao; AppSettings read() { List<AppSettingEntity> listEntity = appSettingsDao.findAll(); Map<String, String> map = new HaspMap<String, String>(); foreach (AppSettingEntity entity : listEntity) { map.put(entity.getConfigName(), entity.getConfigValue()); } return new AppSettings(map); } } DatabaseApplicationSettingReader { dao appSettingDao; AppSettings read() { //read from some properties file return new AppSettings(map); } } Application settings class: AppSettings { private static AppSettings instance; private Map map; Public AppSettings(Map map) { this.map = map; } public static AppSettings getInstance() { if (instance == null) { throw new RuntimeException("Object not configure yet"); } return instance; } public static configure(IApplicationSettingReader reader) { instance = reader.read(); } public String getFtpSetting(String param) { return map.get("ftp." + param); } public String getContentSetting(String param) { return map.get("content." + param); } } Test class: AppSettingsTest { IApplicationSettingReader reader; @Before public void setUp() throws Exception { reader = new DatabaseApplicationSettingReader(); } @Test public void getContentSetting_should_get_content_title() { AppSettings.configure(reader); Instance settings = AppSettings.getInstance(); String title = settings.getContentSetting("title"); assertNotNull(title); Sysout(title); } } My questions are: Can you give your opinion about my code, is there something wrong? I configure my application setting once, while the application start, I configure the application setting with appropriate reader (DbReader or PropertiesReader), I make it singleton. The problem is, when some user edit the database or file directly to database or file, I can't get the changed values. Now, I want to implement something like ApplicationSettingChangeListener. So if the data changes, I will refresh my application settings. Do you have any suggestions how this can be implemented?

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• Creating a spam list with a web crawler in python

  - by user313623

  Hey guys, I'm not trying to do anything malicious here, I just need to do some homework. I'm a fairly new programmer, I'm using python 3.0, and I having difficulty using recursion for problem-solving. I've been stuck on this question for quite a while. Here's the assignment: Write a recursive method spam(url, n) that takes a url of a web page as input and a non-negative integer n, collects all the email address contained in the web page and adds them to a global dictionary variable spam_dict, and then recursively calls itself on every http hyperlink contained in the web page. You will use a dictionary so only one copy of every email address is save; your dictionary will store (key,value) pairs (email, email). The recursive call should use the parameter n-1 instead of n. If n = 0, you should collect the email addresses but no recursive calls should be made. The parameter n is used to limit the recursion to at most depth n. You will need to use the solutions of the two above problems; you method spam() will call the methods links2() and emails() and possibly other functions as well. Notes: 1. running spam() directly will produce no output on the screen; to find your spam_dict, you will need to read the value of spam_dict, and you will also need to reset it to the empty dictionary before every run of spam. 2. Recall how global variables are used. Usage: spam_dict = {} spam('http://reed.cs.depaul.edu/lperkovic/csc242/test1.html',0) spam_dict.keys() dict_keys([]) spam_dict = {} spam('http://reed.cs.depaul.edu/lperkovic/csc242/test1.html',1) spam_dict.keys() dict_keys(['[email protected]', '[email protected]']) So far, I've written a function that traverses web pages and puts all the links in a nice little list, and what I wanted to do was call that functions. And why would I use recursion on a dictionary? And how? I don't understand how n ties into all of this. def links2(url): content = str(urlopen(url).read()) myparser = MyHTMLParser() myparser.feed(content) lst = myparser.get() mergelst = [] for link in lst: mergelst.append(urljoin(lst[0],link)) print(mergelst) Any input (except why spam is bad) would be greatly appreciated. Also, I realize that the above function could probably look better, if you have a way to do it, I'm all ears. However, all I need is the point is for the program to produce the proper output.

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• NO FBML is working in iframe in facebook using PHP (ie or ff or anywhere else!)

  - by Cyprus106

  I have tried for three days now and gotten nowhere on this.... I absolutely can not get any "fb:" code to render anything! I've tried the exact code in the sandbox and it works fine. I've read through every search result I could find and gotten nowhere... I'm using a standard xd_receiver page, and in the body there's this line: < script src="http://static.ak.connect.facebook.com/js/api_lib/v0.4/XdCommReceiver.js" type="text/javascript"></script> Here's my index page. It's basically the stock facebook example code.... <?php require_once 'facebook-platform/php/facebook.php'; //Authentication Keys $appapikey = 'MY_KEY'; // obviously this is my real key $appsecret = 'MY_SECRET'; // same thing $facebook = new Facebook($appapikey, $appsecret); $user_id = $facebook->require_login(); ?> <html xmlns="http://www.w3.org/1999/xhtml" xmlns:fb="http://www.facebook.com/2008/fbml"> <head></head> <body> <script src="http://static.ak.connect.facebook.com/js/api_lib/v0.4/FeatureLoader.js.php" type="text/javascript"></script> <? echo "<p>Hello, <fb:name uid=\"$user_id\" useyou=\"false\"></fb:name>!</p>"; ?> <script type="text/javascript"> FB_RequireFeatures(["XFBML"], function(){ FB.Facebook.init("<?php echo $appapikey; ?>", "xd_receiver.htm"); }); </script> </body> </html> oddly enough, when I put this code below where it echos the logged in user's name, it does show the id numbers of friends. But again, it won't render their names <?php friends.get API method echo "<p>Friends:"; $friends = $facebook->api_client->friends_get(); $friends = array_slice($friends, 0, 25); foreach ($friends as $friend) { echo "<br>".$friend." - <fb:name uid=\".$user_id.\" useyou=\"false\"></fb:name>"; } echo "</p>"; ?> Here's my settings: Canvas Callback URL http://www.my-actual-website.com/test/ Canvas URL http://apps.facebook.com/gogre_testapp/ FBML/iframe iframe Application Type Website Post-Remove URL http://www.my-actual-website.com/test/ Post-Authorize URL http://www.my-actual-website.com/test/ Please, somebody help me out! I've been trying unsuccessfully for days

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• wget not behaving via IPC::Open3 vs bash

  - by Ryley

  I'm trying to stream a file from a remote website to a local command and am running into some problems when trying to detect errors. The code looks something like this: use IPC::Open3; my @cmd = ('wget','-O','-','http://10.10.1.72/index.php');#any website will do here my ($wget_pid,$wget_in,$wget_out,$wget_err); if (!($wget_pid = open3($wget_in,$wget_out,$wget_err,@cmd))){ print STDERR "failed to run open3\n"; exit(1) } close($wget_in); my @wget_outs = <$wget_out>; my @wget_errs = <$wget_err>; print STDERR "wget stderr: ".join('',@wget_errs); #page and errors outputted on the next line, seems wrong print STDERR "wget stdout: ".join('',@wget_outs); #clean up after this, not shown is running the filtering command, closing and waitpid'ing When I run that wget command directly from the command-line and redirect stderr to a file, something sane happens - the stdout will be the downloaded page, the stderr will contain the info about opening the given page. wget -O - http://10.10.1.72/index.php 2> stderr_test_file When I run wget via open3, I'm getting both the page and the info mixed together in stdout. What I expect is the loaded page in one stream and STDERR from wget in another. I can see I've simplified the code to the point where it's not clear why I want to use open3, but the general plan is that I wanted to stream stdout to another filtering program as I received it, and then at the end I was going to read the stderr from both wget and the filtering program to determine what, if anything went wrong. Other important things: I was trying to avoid writing the wget'd data to a file, then filtering that file to another file, then reading the output. It's key that I be able to see what went wrong, not just reading $? 8 (i.e. I have to tell the user, hey, that IP address is wrong, or isn't the right kind of website, or whatever). Finally, I'm choosing system/open3/exec over other perl-isms (i.e. backticks) because some of the input is provided by untrustworthy users.

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• Parallel For Loop - Problems when adding to a List

  - by Kevin Crowell

  I am having some issues involving Parallel for loops and adding to a List. The problem is, the same code may generate different output at different times. I have set up some test code below. In this code, I create a List of 10,000 int values. 1/10th of the values will be 0, 1/10th of the values will be 1, all the way up to 1/10th of the values being 9. After setting up this List, I setup a Parallel for loop that iterates through the list. If the current number is 0, I add a value to a new List. After the Parallel for loop completes, I output the size of the list. The size should always be 1,000. Most of the time, the correct answer is given. However, I have seen 3 possible incorrect outcomes occur: The size of the list is less than 1,000 An IndexOutOfRangeException occurs @ doubleList.Add(0.0); An ArgumentException occurs @ doubleList.Add(0.0); The message for the ArgumentException given was: Destination array was not long enough. Check destIndex and length, and the array's lower bounds. What could be causing the errors? Is this a .Net bug? Is there something I can do to prevent this from happening? Please try the code for yourself. If you do not get an error, try it a few times. Please also note that you probably will not see any errors using a single-core machine. using System; using System.Collections.Generic; using System.Threading.Tasks; namespace ParallelTest { class Program { static void Main(string[] args) { List<int> intList = new List<int>(); List<double> doubleList = new List<double>(); for (int i = 0; i < 250; i++) { intList.Clear(); doubleList.Clear(); for (int j = 0; j < 10000; j++) { intList.Add(j % 10); } Parallel.For(0, intList.Count, j => { if (intList[j] == 0) { doubleList.Add(0.0); } }); if (doubleList.Count != 1000) { Console.WriteLine("On iteration " + i + ": List size = " + doubleList.Count); } } Console.WriteLine("\nPress any key to exit."); Console.ReadKey(); } } }

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• WPF Treeview: How to display rounded border around the selected item?

  - by chikak

  I am trying to set the rounded border around the selected item of the treeview (like the one in the windows explorer on Vista). The problem is that the trigger in the following code doesn't seem to be working. It looks like the IsSelected property is always false. <TreeView x:Name="m_treeView" BorderThickness="0" d:LayoutOverrides="Width, Height"> <TreeView.Resources> <Style TargetType="TreeViewItem"> <Style.Resources> <Brush x:Key="{x:Static SystemColors.HighlightBrushKey}">Transparent</Brush> </Style.Resources> </Style> </TreeView.Resources> <TreeView.ItemTemplate> <HierarchicalDataTemplate DataType="{x:Type local:DirectoryPresentationBase}" ItemsSource="{Binding Children}"> <TreeViewItem> <TreeViewItem.Header> <Border Name="SelectedBorder" CornerRadius="3" Background="#EFF8FD" BorderBrush="#99DEFD" BorderThickness="1" > <StackPanel Orientation="Horizontal"> <interactivity:Interaction.Behaviors> <local:TreeViewExpandBehavior AssociatedTreeView="{Binding ElementName=m_treeView}"/> </interactivity:Interaction.Behaviors> <Image x:Name="img" Width="24" Height="16" Stretch="None" Source="{Binding SmallIcon}"/> <TextBlock Text="{Binding Name}" Margin="5,0" /> </StackPanel> </Border> </TreeViewItem.Header> </TreeViewItem> <HierarchicalDataTemplate.Triggers> <Trigger Property="TreeViewItem.IsSelected" Value="True"> <Setter Property="Background" TargetName="SelectedBorder" Value="Red"/> <Setter Property="BorderBrush" TargetName="SelectedBorder" Value="Green"/> </Trigger> <Trigger Property="TreeViewItem.IsSelected" Value="False"> <Setter Property="Background" TargetName="SelectedBorder" Value="Transparent"/> <Setter Property="BorderBrush" TargetName="SelectedBorder" Value="Transparent"/> </Trigger> </HierarchicalDataTemplate.Triggers> </HierarchicalDataTemplate> </TreeView.ItemTemplate> </TreeView>

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• Optimize date query for large child tables: GiST or GIN?

  - by Dave Jarvis

  Problem 72 child tables, each having a year index and a station index, are defined as follows: CREATE TABLE climate.measurement_12_013 ( -- Inherited from table climate.measurement_12_013: id bigint NOT NULL DEFAULT nextval('climate.measurement_id_seq'::regclass), -- Inherited from table climate.measurement_12_013: station_id integer NOT NULL, -- Inherited from table climate.measurement_12_013: taken date NOT NULL, -- Inherited from table climate.measurement_12_013: amount numeric(8,2) NOT NULL, -- Inherited from table climate.measurement_12_013: category_id smallint NOT NULL, -- Inherited from table climate.measurement_12_013: flag character varying(1) NOT NULL DEFAULT ' '::character varying, CONSTRAINT measurement_12_013_category_id_check CHECK (category_id = 7), CONSTRAINT measurement_12_013_taken_check CHECK (date_part('month'::text, taken)::integer = 12) ) INHERITS (climate.measurement) CREATE INDEX measurement_12_013_s_idx ON climate.measurement_12_013 USING btree (station_id); CREATE INDEX measurement_12_013_y_idx ON climate.measurement_12_013 USING btree (date_part('year'::text, taken)); (Foreign key constraints to be added later.) The following query runs abysmally slow due to a full table scan: SELECT count(1) AS measurements, avg(m.amount) AS amount FROM climate.measurement m WHERE m.station_id IN ( SELECT s.id FROM climate.station s, climate.city c WHERE -- For one city ... -- c.id = 5182 AND -- Where stations are within an elevation range ... -- s.elevation BETWEEN 0 AND 3000 AND 6371.009 * SQRT( POW(RADIANS(c.latitude_decimal - s.latitude_decimal), 2) + (COS(RADIANS(c.latitude_decimal + s.latitude_decimal) / 2) * POW(RADIANS(c.longitude_decimal - s.longitude_decimal), 2)) ) <= 50 ) AND -- -- Begin extracting the data from the database. -- -- The data before 1900 is shaky; insufficient after 2009. -- extract( YEAR FROM m.taken ) BETWEEN 1900 AND 2009 AND -- Whittled down by category ... -- m.category_id = 1 AND m.taken BETWEEN -- Start date. (extract( YEAR FROM m.taken )||'-01-01')::date AND -- End date. Calculated by checking to see if the end date wraps -- into the next year. If it does, then add 1 to the current year. -- (cast(extract( YEAR FROM m.taken ) + greatest( -1 * sign( (extract( YEAR FROM m.taken )||'-12-31')::date - (extract( YEAR FROM m.taken )||'-01-01')::date ), 0 ) AS text)||'-12-31')::date GROUP BY extract( YEAR FROM m.taken ) The sluggishness comes from this part of the query: m.taken BETWEEN /* Start date. */ (extract( YEAR FROM m.taken )||'-01-01')::date AND /* End date. Calculated by checking to see if the end date wraps into the next year. If it does, then add 1 to the current year. */ (cast(extract( YEAR FROM m.taken ) + greatest( -1 * sign( (extract( YEAR FROM m.taken )||'-12-31')::date - (extract( YEAR FROM m.taken )||'-01-01')::date ), 0 ) AS text)||'-12-31')::date The HashAggregate from the plan shows a cost of 10006220141.11, which is, I suspect, on the astronomically huge side. There is a full table scan on the measurement table (itself having neither data nor indexes) being performed. The table aggregates 237 million rows from its child tables. Question What is the proper way to index the dates to avoid full table scans? Options I have considered: GIN GiST Rewrite the WHERE clause Separate year_taken, month_taken, and day_taken columns to the tables What are your thoughts? Thank you!

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• Invalid character in a Base-64 string when Concatenating and Url encoding a string

  - by Rob

  I’m trying to write some encryption code that is passed through a Url. For the sake of the issue I’ve excluded the actual encryption of the data and just shown the code causing the problem. I take a salt value, convert it to a byte array and then convert that to a base64 string. This string I concatenate to another base64 string (which was previously a byte array). These two base64 strings are then Url encoded. Here’s my code... using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Security.Cryptography; using System.IO; using System.Web; class RHEncryption { private static readonly Encoding ASCII_ENCODING = new System.Text.ASCIIEncoding(); private static readonly string SECRET_KEY = "akey"; private static string md5(string text) { return BitConverter.ToString(new MD5CryptoServiceProvider().ComputeHash(ASCII_ENCODING.GetBytes(text))).Replace("-", "").ToLower(); } public string UrlEncodedData; public RHEncryption() { // encryption object RijndaelManaged aes192 = new RijndaelManaged(); aes192.KeySize = 192; aes192.BlockSize = 192; aes192.Mode = CipherMode.CBC; aes192.Key = ASCII_ENCODING.GetBytes(md5(SECRET_KEY)); aes192.GenerateIV(); // convert Ivector to base64 for sending string base64IV = Convert.ToBase64String(aes192.IV); // salt value string s = "maryhadalittlelamb"; string salt = s.Substring(0, 8); // convert to byte array // and base64 for sending byte[] saltBytes = ASCII_ENCODING.GetBytes(salt.TrimEnd('\0')); string base64Salt = Convert.ToBase64String(saltBytes); //url encode concatenated base64 strings UrlEncodedData = HttpUtility.UrlEncode(base64Salt + base64IV, ASCII_ENCODING); } public string UrlDecodedData() { // decode the url encode string string s = HttpUtility.UrlDecode(UrlEncodedData, ASCII_ENCODING); // convert back from base64 byte[] base64DecodedBytes = null; try { base64DecodedBytes = Convert.FromBase64String(s); } catch (FormatException e) { Console.WriteLine(e.Message.ToString()); Console.ReadLine(); } return s; } } If I then call the UrlDecodedData method I get a “Invalid character in a Base-64 string” exception. This is generated because the base64Salt variable contains an invalid character (I’m guessing a line termination) but I can’t seem to strip it off.

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• Parallel For Loop - Problems when adding to a List - Possible .Net Bugs

  - by Kevin Crowell

  I am having some issues involving Parallel for loops and adding to a List. The problem is, the same code may generate different output at different times. I have set up some test code below. In this code, I create a List of 10,000 int values. 1/10th of the values will be 0, 1/10th of the values will be 1, all the way up to 1/10th of the values being 9. After setting up this List, I setup a Parallel for loop that iterates through the list. If the current number is 0, I add a value to a new List. After the Parallel for loop completes, I output the size of the list. The size should always be 1,000. Most of the time, the correct answer is given. However, I have seen 3 possible incorrect outcomes occur: The size of the list is less than 1,000 An IndexOutOfRangeException occurs @ doubleList.Add(0.0); An ArgumentException occurs @ doubleList.Add(0.0); The message for the ArgumentException given was: Destination array was not long enough. Check destIndex and length, and the array's lower bounds. What could be causing the errors? Is this a .Net bug? Is there something I can do to prevent this from happening? Please try the code for yourself. If you do not get an error, try it a few times. Please also note that you probably will not see any errors using a single-core machine. using System; using System.Collections.Generic; using System.Threading.Tasks; namespace ParallelTest { class Program { static void Main(string[] args) { List<int> intList = new List<int>(); List<double> doubleList = new List<double>(); for (int i = 0; i < 250; i++) { intList.Clear(); doubleList.Clear(); for (int j = 0; j < 10000; j++) { intList.Add(j % 10); } Parallel.For(0, intList.Count, j => { if (intList[j] == 0) { doubleList.Add(0.0); } }); if (doubleList.Count != 1000) { Console.WriteLine("On iteration " + i + ": List size = " + doubleList.Count); } } Console.WriteLine("\nPress any key to exit."); Console.ReadKey(); } } }

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• Should we denormalize database to improve performance?

  - by Groo

  We have a requirement to store 500 measurements per second, coming from several devices. Each measurement consists of a timestamp, a quantity type, and several vector values. Right now there is 8 vector values per measurement, and we may consider this number to be constant for needs of our prototype project. We are using HNibernate. Tests are done in SQLite (disk file db, not in-memory), but production will probably be MsSQL. Our Measurement entity class is the one that holds a single measurement, and looks like this: public class Measurement { public virtual Guid Id { get; private set; } public virtual Device Device { get; private set; } public virtual Timestamp Timestamp { get; private set; } public virtual IList<VectorValue> Vectors { get; private set; } } Vector values are stored in a separate table, so that each of them references its parent measurement through a foreign key. We have done a couple of things to ensure that generated SQL is (reasonably) efficient: we are using Guid.Comb for generating IDs, we are flushing around 500 items in a single transaction, ADO.Net batch size is set to 100 (I think SQLIte does not support batch updates? But it might be useful later). The problem Right now we can insert 150-200 measurements per second (which is not fast enough, although this is SQLite we are talking about). Looking at the generated SQL, we can see that in a single transaction we insert (as expected): 1 timestamp 1 measurement 8 vector values which means that we are actually doing 10x more single table inserts: 1500-2000 per second. If we placed everything (all 8 vector values and the timestamp) into the measurement table (adding 9 dedicated columns), it seems that we could increase our insert speed up to 10 times. Switching to SQL server will improve performance, but we would like to know if there might be a way to avoid unnecessary performance costs related to the way database is organized right now. [Edit] With in-memory SQLite I get around 350 items/sec (3500 single table inserts), which I believe is about as good as it gets with NHibernate (taking this post for reference: http://ayende.com/Blog/archive/2009/08/22/nhibernate-perf-tricks.aspx). But I might as well switch to SQL server and stop assuming things, right? I will update my post as soon as I test it.

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