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• Temporary storage for keeping data between program iterations?

  - by mr.b

  I am working on an application that works like this: It fetches data from many sources, resulting in pool of about 500,000-1,500,000 records (depends on time/day) Data is parsed Part of data is processed in a way to compare it to pre-existing data (read from database), calculations are made, and stored in database. Resulting dataset that has to be stored in database is, however, much smaller in size (compared to original data set), and ranges from 5,000-50,000 records. This process almost always updates existing data, perhaps adds few more records. Then, data from step 2 should be kept somehow, somewhere, so that next time data is fetched, there is a data set which can be used to perform calculations, without touching pre-existing data in database. I should point out that this data can be lost, it's not irreplaceable (key information can be read from database if needed), but it would speed up the process next time. Application components can (and will be) run off different computers (in the same network), so storage has to be reachable from multiple hosts. I have considered using memcached, but I'm not quite sure should I do so, because one record is usually no smaller than 200 bytes, and if I have 1,500,000 records, I guess that it would amount to over 300 MB of memcached cache... But that doesn't seem scalable to me - what if data was 5x that amount? If it were to consume 1-2 GB of cache only to keep data in between iterations (which could easily happen)? So, the question is: which temporary storage mechanism would be most suitable for this kind of processing? I haven't considered using mysql temporary tables, as I'm not sure if they can persist between sessions, and be used by other hosts in network... Any other suggestion? Something I should consider?

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• Hiding a button on pushed view and showing it when back to list view

  - by torr

  When I load my list view it has several blog posts and a refresh button on the top left. If I tap on a list item a view is pushed with the contents of that specific post. When this view is pushed in, the refresh button is hidden. But when I tap 'Back' to the parent list view, I'd like the refresh button to show (un-hide) - but it remains hidden. Any idea how to make this work? This is my View: Ext.require(['Ext.data.Store', 'MyApp.model.StreamModel'], function() { Ext.define('MyApp.view.HomeView', { extend: 'Ext.navigation.View', xtype: 'homepanel', requires: [ 'Ext.dataview.List', ], config: { title: 'Home', iconCls: 'home', styleHtmlContent: true, navigationBar: { items: [ { xtype: 'button', iconMask: true, iconCls: 'refresh', align: 'left', action: 'refreshButton', id: 'refreshButtonId' } ] }, items: { title: 'My', xtype: 'list', itemTpl: [ '<div class="post">', ... '</div>' ].join(''), store: new Ext.data.Store({ model: 'MyApp.model.StreamModel', autoLoad: true, storeId: 'stream' }), } } }); }); and my Controller: Ext.define('MyApp.controller.SingleController', { extend: 'Ext.app.Controller', config: { refs: { stream: 'homepanel' }, control: { 'homepanel list': { itemtap: 'showPost' } } }, showPost: function(list, index, element, record) { this.getStream().push({ xtype: 'panel', html: [ '<div class="post">', '</div>' ].join(''), scrollable: 'vertical', styleHtmlContent: true, }); Ext.getCmp('refreshButtonId').hide(); } });

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• 1 oracle schema support large reques per day , is this safe ?

  - by Hlex

  I 'm java system designer. As we have large project to do tightly, Those projects are java api without webpage. I design to create general flow engine to support all project. This idea use 1 oracle schema , having general transaction table . And others control routing table. They all nearly complete. But DBA Team concern that he is suffered to maintain very large request to 1 schema. 1 reason is if there are problem is some table. He must offline tablespace to fix. This is problem because all project will be affected. I try to convince by split data of each table to partition by project_code & "month number to delete" . Eaxmple partition: PROJ1_05 PROJ1_06 PROJ1_07 PROJ2_05 PROJ2_06 PROJ2_07 and all transaction table will store on its partition. So, If there are problem on any part of tablespace then he should offline some partition and another project with use same table should able to service Transaction per day should around 10Meg Record per day. Is this a good idea? If I must use 1 schema, what is strategy to do? Do you have any comment?

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• problem with mysql character set & GWT

  - by Ehsan Khodarahmi

  Hi I've a SmartGWT application which interacts with a mysql database using rpc services. Suppose it as a simple form with a textbox & two save & load buttons. My database & tables & all fields collation is utf8_persian_ci. All java source files & module html & xml files have saved with utf8 character set. & also I've a meta tag in module html file which contains my form : <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> my application works correctly in eclipse develpment mode & also in my local tomcat server. Then i put it on remote server (I compress it using jar.exe into a war file with -cvf flag & then upload it using my server's plesk control panel). In this mode, when I load data from a mysql table (load a record from any table), data will load into my form with no problem, but when I want to save some data (in persian language), mysql just writes some ? (question sign) in characteristic table fields. Any idea ?

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• LINQ to XML contents of child records.

  - by Fossaw

  I have this LINQ to XML enquiry... var Records = from Item in XDoc.Root.Elements("Item") where (string)Item.Element("ItemNumber") == item.ID.ToString select Item; ... where ItemNumber is a reference number used in the XML, (originally written by this program but manually edited by "others"), and item.ID is the database version of the same thing. The query executes, and I can test for the number of entries in the result fine... if (Records.Count() < 1) ... you get the idea. I have established that there is only one record. Each Item has several child fields. I want to test the values of the child fields are reasonable before passing them on to the database update sub-system. The XML is produced by the program, but edited by users, so I need to really check what is coming back. So I tried... if (DB_English.ToString() != Records.Elements("English").ToString()) ... DB_English is from the database, but the XML in Records, does not contain the contents of that field, it contains... System.Xml.Linq.Extensions+<GetElements>d__29`1[System.Xml.Linq.XElement] ... so, how do I get the value of this element in the XML file? I need to check the field in the XML has not been altered, (the manual editors of this data file are not potentially 100% reliable).

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• Rspec Selenium. Test to check certain Ajax functions passes when i expect it to fail.

  - by alokswain

  I am testing a Ajax action using Rspec and Selenium. My story is as follows: it "should create a new User with any input" do @browser.open "/people" @browser.wait_for_page_to_load "2000" @browser.type "user_name", "Alok Swain" @browser.click "user_submit" @browser.text?("Alok Swain").should be_true end The action i am testing is: def add_user @users = User.all User.create(params[:user]) render :update do |page| page.alert "Created User" page.replace_html "users", :partial => '/people/users_list', :locals => {:users => @users} end end The test fails and the error I get is: 'User should create a new User with any input' FAILED expected false to be true. This test should pass right ? I also kept an alert and tried @browser.is_alert_present.should be_true but i got the same error. I tried @browser.is_text_present("test") and this test succeeded. In the test database a record was created for Alok Swain but when I tried the above assertion it passed when i expected it to fail. Is there any thing else to be done here. What am I missing ?

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• PHP: Aggregate Model Classes or Uber Model Classes?

  - by sunwukung

  In many of the discussions regarding the M in MVC, (sidestepping ORM controversies for a moment), I commonly see Model classes described as object representations of table data (be that an Active Record, Table Gateway, Row Gateway or Domain Model/Mapper). Martin Fowler warns against the development of an anemic domain model, i.e. a class that is nothing more than a wrapper for CRUD functionality. I've been working on an MVC application for a couple of months now. The DBAL in the application I'm working on started out simple (on account of my understanding - oh the benefits of hindsight), and is organised so that Controllers invoke Business Logic classes, that in turn access the database via DAO/Transaction Scripts pertinent to the task at hand. There are a few "Entity" classes that aggregate these DAO objects to provide a convenient CRUD wrapper, but also embody some of the "behaviour" of that Domain concept (for example, a user - since it's easy to isolate). Taking a look at some of the code, and thinking along refactoring some of the code into a Rich Domain Model, it occurred to me that were I to try and wrap the CRUD routines and behaviour of say, a Company into a single "Model" class, that would be a sizeable class. So, my question is this: do Models represent domain objects, business logic, service layers, all of the above combined? How do you go about defining the responsibilities for these components?

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• Compressibility Example

  - by user285726

  From my algorithms textbook: The annual county horse race is bringing in three thoroughbreds who have never competed against one another. Excited, you study their past 200 races and summarize these as prob- ability distributions over four outcomes: first (“first place”), second, third, and other. Outcome Aurora Whirlwind Phantasm 0.15 0.30 0.20 first 0.10 0.05 0.30 second 0.70 0.25 0.30 third 0.05 0.40 0.20 other Which horse is the most predictable? One quantitative approach to this question is to look at compressibility. Write down the history of each horse as a string of 200 values (first, second, third, other). The total number of bits needed to encode these track- record strings can then be computed using Huffman’s algorithm. This works out to 290 bits for Aurora, 380 for Whirlwind, and 420 for Phantasm (check it!). Aurora has the shortest encoding and is therefore in a strong sense the most predictable. How did they get 420 for Phantasm? I keep getting 400 bytes, as so: Combine first, other = 0.4, combine second, third = 0.6. End up with 2 bits encoding each position. Is there something I've misunderstood about the Huffman encoding algorithm? Textbook available here: http://www.cs.berkeley.edu/~vazirani/algorithms.html (page 156).

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• Conditional "Get Script File" in Javascript without using a library function

  - by Adam

  I work at a company that has many clients that have their own website that "plugs in" to our system. In other words they have their own website and they have a link that, when the user clicks it, transitions them over to our site. There is a feature that I want to track by giving the client a small block of code to put on their homepage. Whenever the homepage is loaded with a certain query string variable I want the block of code to request a file on my server. Then on the server I'll record the tracking info based on the query string. All this would be really easy if I can guarantee that the client would be using jQuery or some similar library, but there are a lot of clients and I can't really rely on them all using jQuery. At the same time I'd like to limit the size of the block of javascript code that they paste in. I think the best solution would be to have something like: if(querystring.substring("Tracking=") > 0) { include("blah.aspx?TrackingQS=" + querystring); } but I can't find a include function in built-in javascript without calling some library like jQuery. Any thoughts?? I could do straight up AJAX but I want to limit the number of lines of code for several reasons that I won't bore you with here.

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• Saving multiple objects in a single call in rails

  - by CaptnCraig

  I have a method in rails that is doing something like this: a = Foo.new("bar") a.save b = Foo.new("baz") b.save ... x = Foo.new("123", :parent_id => a.id) x.save ... z = Foo.new("zxy", :parent_id => b.id) z.save The problem is this takes longer and longer the more entities I add. I suspect this is because it has to hit the database for every record. Since they are nested, I know I can't save the children before the parents are saved, but I would like to save all of the parents at once, and then all of the children. It would be nice to do something like: a = Foo.new("bar") b = Foo.new("baz") ... saveall(a,b,...) x = Foo.new("123", :parent_id => a.id) ... z = Foo.new("zxy", :parent_id => b.id) saveall(x,...,z) That would do it all in only two database hits. Is there an easy way to do this in rails, or am I stuck doing it one at a time?

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• Avoiding Duplicate Data in DB (for use with Rails)

  - by ants

  I have five tables that I am trying to get to work nicely together but may need some help. I have three main tables: accounts members and roles. With two join tables account_members and account_member_roles. The accounts and members table are joined by account_members (fk account_id and member_id) table. The other 2 tables are the problem (roles and account_member_roles). A member of an account can have more than one role and I have the account_member_roles (fk account_member_id and role_id) table joining the account_members join table and the roles table. That seems logical but can you have a relationship with a join table? What I'd like to be able to do is when creaeting an account, for instance, I would like @account.save to include the roles and update the account_member_roles table neatly ..... but through the account_members join table. I've tried ..... accept_nested_attributes_for :members, :account_member_roles in the account.rb but I get ..... ActiveRecord::HasManyThroughCantAssociateThroughHasManyReflection (Cannot modify association 'Account#account_member_roles' because the source reflection class 'AccountMemberRole' is associated to 'AccountMember' via :has_many.) upon trying to save a record. Any advice on how I should approach this? CIA -ants

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• Extract primary key from MySQL in PHP

  - by Parth

  I have created a PHP script and I am lacking to extract the primary key, I have given flow below, please help me in how can i modify to get primary key I am using MySQL DB, working for Joomla, My requirement is tracking the activity like insert/update/delete on any table and store it in another audit table using triggers, i.e. I am doing Auditing. DB's table structure: Few tables dont have any PK nor auto increment key Flow of my script is : I fetch out all table from DB. I check whether the table have any trigger or not. If yes then it moves to check nfor next table and so on. If it does'nt find any trigger then it creates the triggers for the table, such that, -it first checks if the table has any primary key or not(for inserting in Tracking audit table for every change made) if it has the primary key then it uses it further in creation of trigger. if it doesnt find any PK then it proceeds further in creating the trigger without inserting any id in audit table Now here, My problem is I need the PK every time so that I can record the id of any particular table in which the insert/update/delete is performed, so that further i can use this audit track table to replicate in production DB.. Now as I haave mentioned earlier that I am not available with PK/auto-incremented in some table, then what should I do get the particular id in which change is done? please guide me...GEEKS!!!

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• Sql query - selecting top 5 rows and further selecting rows only if User is present

  - by Gublooo

  Hello, I kind of stuck on how to implement this query - this is pretty similar to the query I posted earlier but I'm not able to crack it. I have a shopping table where everytime a user buys anything, a record is inserted. Some of the fields are * shopping_id (primary key) * store_id * user_id Now what I need is to pull only the list of those stores where he's among the top 5 visitors: When I break it down - this is what I want to accomplish: * Find all stores where this UserA has visited * For each of these stores - see who the top 5 visitors are. * Select the store only if UserA is among the top 5 visitors. The corresponding queries would be: select store_id from shopping where user_id = xxx select user_id,count(*) as 'visits' from shopping where store_id in (select store_id from shopping where user_id = xxx) group by user_id order by visits desc limit 5 Now I need to check in this resultset if UserA is present and select that store only if he's present. For example if he has visited a store 5 times - but if there are 5 or more people who have visited that store more than 5 times - then that store should not be selected. So I'm kind of lost here. Thanks for your help

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• Search book by title, and author

  - by Swoosh

  I got a table with columns: author firstname, author lastname, and booktitle Multiple users are inserting in the database, through an import, and I'd like to avoid duplicates. So I'm trying to do something like this: I have a record in the db: First Name: "Isaac" Last Name: "Assimov" Title: "I, Robot" If the user tries to add it again, it would be basically a non-split-text (would not be split up into author firstname, author lastname, and booktitle) So it would basically look like this: "Isaac Asimov - I Robot" or "Asimov, Isaac - I Robot" or "I Robot by Isaac Asimov" You see where I am getting at? (I cannot force the user to split up all the books into into author firstname, author lastname, and booktitle, and I don't even like the idea to force the user, because it's not too user-friendly) What is the best way (in SQL) to compare all this possible bookdata scenarios to what I have in the database, not to add the same book twice. I was thinking about a possibility of suggesting the user: "is THIS the book you are trying to add?" (imagine a list instead of the THIS word, just like on stackoverflow - ask question - Related Questions. I was thinking about soundex and maybe even the like operators, but so far i didn't get the results i was hoping.

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• What do these C# auto-generated table adapter commands do? e.g. UPDATE/INSERT followed by a SELECT

  - by RickL

  I'm working with a legacy application which I'm trying to change so that it can work with SQL CE, whilst it was originally written against SQL Server. The problem I am getting now is that when I try to do dataAdapter.Update, SQL CE complains that it is not expecting the SELECT keyword in the command text. I believe this is because SQL CE does not support batch SELECT statements. The auto-generated table adapter command looks like this... this._adapter.InsertCommand.CommandText = @"INSERT INTO [Table] ([Field1], [Field2]) VALUES (@Value1, @Value2); SELECT Field1, Field2 FROM Table WHERE (Field1 = @Value1)"; What is it doing? It looks like it is inserting new records from the datatable into the database, and then reading that record back from the database into the datatable? What's the point of that? Can I just go through the code and remove all these SELECT statements? Or is there an easier way to solve my problem of wanting to use these data adapters with SQL CE? I cannot regenerate these table adapters, as the people who knew how to have long since left.

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• LINQ TO SQL error: An attempt has been made to Attach or Add an entity that is not new...

  - by Collin Estes

  "An attempt has been made to Attach or Add an entity that is not new, perhaps having been loaded from another DataContext. This is not supported." I have scene a lot of solutions dealing with the Attach() method but I'm just trying to add in a new record. Not sure what is going on. Here is my code, It is failing on the star'd line.: try { LINQDataContext datacontext = new LINQDataContext(); TrackableItem ti = datacontext.TrackableItems.FirstOrDefault(_t => _t.pkId == obj.fkTrackableItemId); arcTrackableItem ati = new arcTrackableItem(); ati.barcode = ti.barcode; ati.dashNumber = ti.dashNumber; ati.dateDown = ti.dateDown; ati.dateUp = ti.dateUp; ati.fkItemStatusId = ti.fkItemStatusId; ati.fkItemTypeId = ti.fkItemTypeId; ati.partNumber = ti.partNumber; ati.serialNumber = ti.serialNumber; ati.archiveDate = DateTime.Now; datacontext.arcTrackableItems.InsertOnSubmit(ati); datacontext.SubmitChanges(); arcPWR aItem = new arcPWR(); aItem.comments = obj.comments; aItem.fkTrackableItemId = ati.pkId; aItem.fkPWRStatusId = obj.fkPWRStatusId; aItem.PwrStatus = obj.PwrStatus; **datacontext.arcPWRs.InsertOnSubmit(aItem);** datacontext.SubmitChanges();

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• Reading same file from multiple threads in C#

  - by Gustavo Rubio

  Hi. I was googling for some advise about this and I found some links. The most obvious was this one but in the end what im wondering is how well my code is implemented. I have basically two classes. One is the Converter and the other is ConverterThread I create an instance of this Converter class that has a property ThreadNumber that tells me how many threads should be run at the same time (this is read from user) since this application will be used on multi-cpu systems (physically, like 8 cpu) so it is suppossed that this will speed up the import The Converter instance reads a file that can range from 100mb to 800mb and each line of this file is a tab-delimitted value record that is imported to another destination like a database. The ConverterThread class simply runs inside the thread (new Thread(ConverterThread.StartThread)) and has event notification so when its work is done it can notify the Converter class and then I can sum up the progress for all these threads and notify the user (in the GUI for example) about how many of these records have been imported and how many bytes have been read. It seems, however that I'm having some trouble because I get random errors about the file not being able to be read or that the sum of the progress (percentage) went above 100% which is not possible and I think that happens because threads are not being well managed and probably the information returned by the event is malformed (since it "travels" from one thread to another) Do you have any advise on better practices of implementation of threads so I can accomplish this? Thanks in advance.

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• error detection/correction/recovery in serial protocols

  - by Jason S

  I have some designing to do for a serial protocol and am running into some questions that I figure must have been considered elsewhere. So I'm wondering if there are some recommendations for best practices in designing serial protocols. (Please either state a fact that is easily verifiable, or cite a reputable source if you make a claim.) General recommendations for websites/books are also welcome. In particular I have to deal with issues like parsing a stream of bytes into packets verifying a packet is correct (easy with a CRC, for instance) identifying reasonable types of errors that can occur (e.g. in a point-to-point serial stream, sporadic single bit errors, and dropped series of bytes, are both likely, but extra phantom bytes are unlikely; whereas with a record stored in flash memory or on a disk drive the types of errors that predominate are different) error correction or recovery (if I detect an error in a packet, can I correct it? If not, can I resync to the boundary of the next packet?) how to make variable-length packets robust to error correction / recovery. Any suggestions?

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• Deleting a resource in a Cucumber (Capybara) step doesn't work

  - by Josiah Kiehl

  Here is my Scenario: Scenario: Delete a match Given pojo is logged in And there is a match with the following: | game_id | 1 | | name | Game del Pojo | | date_and_time | 2010-02-23 17:52:00 | | players | 2 | | teams | 2 | | comment | This is an awesome comment | | user_id | 1 | And I am on the show match 1 page And show me the page When I follow "Delete" And I follow "Yes, delete it" Then there should not be a match with the following: | game_id | 1 | | name | Game del Pojo | | date_and_time | 2010-02-23 17:52:00 | | players | 2 | | teams | 2 | | comment | This is an awesome comment | | user_id | 1 | If I walk through these steps manually, they work. When I click the confirmation: Yes, delete it, then the match is deleted. Cucumber, however, fails to delete the record and the last step fails. And I follow "Yes, delete it" # features/step_definitions/web_steps.rb:32 Then there should not be a match with the following: # features/step_definitions/match_steps.rb:8 | game_id | 1 | | name | Game del Pojo | | date_and_time | 2010-02-23 17:52:00 | | players | 2 | | teams | 2 | | comment | This is an awesome comment | | user_id | 1 | <nil> expected but was <#<Match id: 1, name: "Game del Pojo", date_and_time: "2010-02-23 17:52:00", teams: 2, created_at: "2010-03-02 23:06:33", updated_at: "2010-03-02 23:06:33", comment: "This is an awesome comment", players: 2, game_id: 1, user_id: 1>>. (Test::Unit::AssertionFailedError) /usr/lib/ruby/1.8/test/unit/assertions.rb:48:in `assert_block' /usr/lib/ruby/1.8/test/unit/assertions.rb:495:in `_wrap_assertion' /usr/lib/ruby/1.8/test/unit/assertions.rb:46:in `assert_block' /usr/lib/ruby/1.8/test/unit/assertions.rb:83:in `assert_equal' /usr/lib/ruby/1.8/test/unit/assertions.rb:172:in `assert_nil' ./features/step_definitions/match_steps.rb:22:in `/^there should (not)? be a match with the following:$/' features/matches.feature:124:in `Then there should not be a match with the following:' Any clue how to debug this? Thanks!

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• How to handle dates that repeat indefinitely

  - by Addsy

  I am implementing a fairly simple calendar on a website using PHP and MySQL. I want to be able to handle dates that repeat indefinitely and am not sure of the best way to do it. For a time limited repeating event it seems to make sense to just add each event within the timeframe into my db table and group them with some form of recursion id. But when there is no limit to how often the event repeats, is it better to a) put records in the db for a specific time frame (eg the next 2 years) and then periodically check and add new records as time goes by - The problem with this is that if someone is looking 3 years ahead, the event won't show up b) not actually have records for each event but instead when i check in my php code for events within a specified time period, calculate wether a repeated event will occur within this time period - The problem with this is that it means there isn't a specific record for each event which i can see being a pain when i then want to associate other info (attendance etc) with that event. It also seems like it might be a bit slow Has anyone tried either of these methods? If so how did it work out? Or is there some other ingenious crafty method i'm missing?

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• Django sitemap intermittent www

  - by Jen Z

  The automatic sitemap for my Django site fluctuates between including the www on urls and leaving it out (I'm aiming to have it in all the time). This has ramifications in google not indexing my pages properly so I'm trying to narrow down what would be causing this issue. I have set PREPEND_WWW = True and my site record in the sites framework is set to include the www e.g. it's set to www.example.com as opposed to example.com. I'm using memcached but pages should expire from the cache after 48 hours so I wouldn't have thought that would be causing the issue? You can see the problem in effect at http://www.livingspaceltd.co.uk/sitemap.xml (refresh the page a few times). My sitemaps setup is fairly prosaic so I'm doubtful that that is the issue, but in case it's something obvious I'm missing here's the code: ***urls.py*** sitemaps = { 'subpages': Subpages_Sitemap, 'standalone_pages': Standalone_Sitemap, 'categories': Categories_Sitemap, } urlpatterns = patterns('', (r'^sitemap\.xml$', 'django.contrib.sitemaps.views.sitemap', {'sitemaps': sitemaps}), ... ***sitemaps.py*** # -*- coding: utf-8 -*- from django_ls.livingspace.models import Page, Category, Standalone_Page, Subpage from django.contrib.sitemaps import Sitemap class Subpages_Sitemap(Sitemap): changefreq = "monthly" priority = 0.4 def items(self): return Subpage.objects.filter(restricted_to__isnull=True) class Standalone_Sitemap(Sitemap): changefreq = "weekly" priority = 1 def items(self): return Standalone_Page.objects.all() class Categories_Sitemap(Sitemap): changefreq = "weekly" priority = 0.7 def items(self): return Category.objects.all()

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• Using Constraints on Hierarchical Data in a Self-Referential Table

  - by pbarney

  Suppose you have the following table, intended to represent hierarchical data: +--------+-------------+ | Field | Type | +--------+-------------+ | id | int(10) | | parent | int(10) | | name | varchar(45) | +--------+-------------+ The table is self-referential in that the parent_id refers to id. So you might have the following data: +----+--------+---------------+ | id | parent | name | +----+--------+---------------+ | 1 | 0 | fruit | | 2 | 0 | vegetable | | 3 | 1 | apple | | 4 | 1 | orange | | 5 | 3 | red delicious | | 6 | 3 | granny smith | | 7 | 3 | gala | +----+--------+---------------+ Using MySQL, I am trying to impose a (self-referential) foreign key constraint upon the data to update on cascades and prevent deletion of fruit if they have "children." So I used the following: CREATE TABLE `idtlp_main`.`fruit` ( `id` INT(10) UNSIGNED NOT NULL AUTO_INCREMENT, `parent` INT(10) UNSIGNED, `name` VARCHAR(45) NOT NULL, PRIMARY KEY (`id`), CONSTRAINT `fk_parent` FOREIGN KEY (`parent`) REFERENCES `fruit` (`id`) ON UPDATE CASCADE ON DELETE RESTRICT ) ENGINE = InnoDB; From what I understand, this should fit my requirements. (And parent must default to null to allow insertions, correct?) The problem is, if I change the id of a record, it will not cascade: Cannot delete or update a parent row: a foreign key constraint fails (`iddoc_main`.`fruit`, CONSTRAINT `fk_parent` FOREIGN KEY (`parent`) REFERENCES `fruit` (`id`) ON UPDATE CASCADE) What am I missing? Feel free to correct me if my terminology is screwed up... I'm new to constraints.

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• XElement vs Dcitionary

  - by user135498

  Hi All, I need advice. I have application that imports 10,000 rows containing name & address from a text file into XElements that are subsequently added to a synchronized queue. When the import is complete the app spawns worker threads that process the XElements by deenqueuing them, making a database call, inserting the database output into the request document and inserting the processed document into an output queue. When all requests have been processed the output queue is written to disk as an XML doc. I used XElements for the requests because I needed the flexibility to add fields to the request during processing. i.e. Depending on the job type the app might require that it add phone number, date of birth or email address to a request based on a name/address match against a public record database. My questions is; The XElements seems to use quite a bit of memory and I know there is a lot of parsing as the document makes its way through the processing methods. I’m considering replacing the XElements with a Dictionary object but I’m skeptical the gain will be worth the effort. In essence it will accomplish the same thing. Thoughts?

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• What's the best way to select max over multiple fields in SQL?

  - by allyourcode

  The I kind of want to do is select max(f1, f2, f3). I know this doesn't work, but I think what I want should be pretty clear (see update 1). I was thinking of doing select max(concat(f1, '--', f2 ...)), but this has various disadvantages. In particular, doing concat will probably slow things down. What's the best way to get what I want? update 1: The answers I've gotten so far aren't what I'm after. max works over a set of records, but it compares them using only one value; I want max to consider several values, just like the way order by can consider several values. update 2: Suppose I have the following table: id class_name order_by1 order_by_2 1 a 0 0 2 a 0 1 3 b 1 0 4 b 0 9 I want a query that will group the records by class_name. Then, within each "class", select the record that would come first if you ordered by order_by1 ascending then order_by2 ascending. The result set would consist of records 2 and 3. In my magical query language, it would look something like this: select max(* order by order_by1 ASC, order_by2 ASC) from table group by class_name

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• desing pattern for related inputs

  - by curiousMo

  My question is a design question : let's say i have a data entry web page with 4 drop down lists, each depending on the previous one, and a bunch of text boxes. country (ddl), state (ddl), city (ddl), boro (ddl), address (txtBox), zipcode(txtbox). and an object that represents a datarow with a value for each. naturally the country, state, city and boro values will be values of primary keys of some lookup tables. when the user chooses to edits that record, i would load it from database and load it into the page. the issue that I have is how to streamline loading the ddls. i have some code that would grab the object, look thru its values and move them to their corresponding input controls in one shot. but in this case i will have to load possible values of country, then assign values, then load values of state, then assign value ans so on. I guess i am looking for an elegant solution. i am using asp.net, but i think it is irrelevant to the question. i am looking more into a design pattern. thanks

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