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• Is it better to use a relational database or document-based database for an app like Wufoo?

  - by mboyle

  I'm working on an application that's similar to Wufoo in that it allows our users to create their own databases and collect/present records with auto generated forms and views. Since every user is creating a different schema (one user might have a database of their baseball card collection, another might have a database of their recipes) our current approach is using MySQL to create separate databases for every user with its own tables. So in other words, the databases our MySQL server contains look like: main-web-app-db (our web app containing tables for users account info, billing, etc) user_1_db (baseball_cards_table) user_2_db (recipes_table) .... And so on. If a user wants to set up a new database to keep track of their DVD collection, we'd do a "create database ..." with "create table ...". If they enter some data in and then decide they want to change a column we'd do an "alter table ....". Now, the further along I get with building this out the more it seems like MySQL is poorly suited to handling this. 1) My first concern is that switching databases every request, first to our main app's database for authentication etc, and then to the user's personal database, is going to be inefficient. 2) The second concern I have is that there's going to be a limit to the number of databases a single MySQL server can host. Pretending for a moment this application had 500,000 user databases, is MySQL designed to operate this way? What if it were a million, or more? 3) Lastly, is this method going to be a nightmare to support and scale? I've never heard of MySQL being used in this way so I do worry about how this affects things like replication and other methods of scaling. To me, it seems like MySQL wasn't built to be used in this way but what do I know. I've been looking at document-based databases like MongoDB, CouchDB, and Redis as alternatives because it seems like a schema-less approach to this particular problem makes a lot of sense. Can anyone offer some advice on this?

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• Finding missing files by checksum

  - by grw

  Hi there, I'm doing a large data migration between two file systems (let's call them F1 and F2) on a Linux system which will necessarily involve copying the data verbatim into a differently-structured hierarchy on F2 and changing the file names. I'd like to write a script to generate a list of files which are in F1 but not in F2, i.e. the ones which weren't copied by the migration script into the new hierarchy, so that I can go back and migrate them manually. Unfortunately for reasons not worth going into, the migration script can't be modified to list files that it doesn't migrate. My question differs from this previously answered one because of the fact that I cannot rely on filenames as a comparison. I know the basic outline of the process would be: Generate a list of checksums for all files, recursing through F1 Do the same for F2 Compare the lists and generate a negative intersection of the checksums, ignoring the file names, to find files which are in F1 but not in F2. I'm kind of stuck getting past that stage, so I'd appreciate any pointers on which tools to use. I think I need to use the 'comm' command to compare the list of file checksums, but since md5sum, sha512sum and the like put the file name next to the checksum, I can't see a way to get it to bring me a useful comparison. Maybe awk is the way to go? I'm using Red Hat Enterprise Linux 5.x. Thanks.

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• Where clause on joined table used for user defined key/value pairs

  - by Steve Wright

  Our application allows administrators to add “User Properties” in order for them to be able to tailor the system to match their own HR systems. For example, if your company has departments, you can define “Departments” in the Properties table and then add values that correspond to “Departments” such as “Jewelry”, “Electronics” etc… You are then able to assign a department to users. Here is the schema: In this schema, a User can have only one UserPropertyValue per Property, but doesn’t have to have a value for the property. I am trying to build a query that will be used in SSRS 2005 and also have it use the PropertyValues as the filter for users. My query looks like this: SELECT UserLogin, FirstName, LastName FROM Users U LEFT OUTER JOIN UserPropertyValues UPV ON U.ID = UPV.UserID WHERE UPV.PropertyValueID IN (1, 5) When I run this, if the user has ANY of the property values, they are returned. What I would like to have is where this query will return users that have values BY PROPERTY. So if PropertyValueID = 1 is of Department (Jewelry), and PropertyValueID = 5 is of EmploymentType (Full Time), I want to return all users that are in Department Jewelry that are EmployeeType of Full Time, can this be done? Here's a full data example: User A has Department(Jewelry value = 1) and EmploymentType(FullTime value = 5)User B has Department(Electronics value = 2) and EmploymentType(FullTime value = 5)User C has Department(Jewelry value = 1) and EmployementType(PartTime value = 6) My query should only return User A using the above query UPDATE: I should state that this query is used as a dataset in SSRS, so the parameter passed to the query will be @PropertyIDs and it is defined as a multi-value parameter in SSRS. WHERE UPV.PropertyValueID IN (@PropertyIDs)

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• Why is this Java Calendar comparison bad?

  - by joe7pak

  Hello folks. I'm having an inexplicable problem with the Java Calendar class when I'm trying to compare to dates. I'm trying to compare to Calendars and determine if their difference is than 1 day, and do things bases on that difference or not. But it doesn't work. If I do this with the two dates: String currDate = aCurrentUTCCalendar.getTime().toString(); String localDate = aLocalCalendar.getTime().toString(); I get these results: currDate = "Thu Jan 06 05:58:00 MST 2010" localDate = "Tue Jan 05 00:02:00 MST 2010" This is correct. But if I do this: long curr = aCurrentUTCCalendar.getTime().getTime(); long local = aLocalCalendar.getTime().getTime(); I get these results: ( in milliseconds since the epoch ) curr = -125566110120000 local = 1262674920000 Since there is only about a 30 hour different between the two, the magnitudes are vastly different, not to mention that annoying negative sign. This causes problems if I do this: long day = 60 * 60 * 24 * 1000; // 86400000 millis, one day if( local - curr > day ) { // do something } What's wrong? Why are the getTime().toString() calls correct, but the getTime().getTime() calls are vastly different? I'm using jdk 1.6_06 on WinXP. I can't upgrade the JDK for various reasons.

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• Best Method For High Data Availability for SQL Server

  - by omatase

  I have a web service that runs 24/7. Periodically it needs to refresh its database with data from another web service. There is a lot of data. It's tens of thousands of rows. (no, I don't mean this is a lot of data for SQL Server, just trying to point out that I expect it to take some time to come down the pipe from the other web service) The data refresh can take between 5 and 10 minutes. The actual data update portion of that is between 1 and 2 minutes. This means the service would be down for all intents and purposes when consumers would be requesting this type of data. I would like to implement a system where data is always available. The only thing that comes to mind is some type of system where I maintain two separate databases. I populate the inactive one, swapping it to active before populating the other one. I'm not sure I know the best way to do this. My current ideas just revolve around two sets of the schema in a single database (using views to access the active set) or two databases each with the same schema. The application would rotate between the two databases. Any suggestions from someone who has done something like this before?

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• Parse large XML file w/ script or use BioPython API ?

  - by jeremy04

  Hey guys this is my first question on here. I'm trying to make a local copy of the UniprotKB in SQL. The UniprotKB is 2.1GB, and it comes in XML and a special text format used by SwissProt Here are my options: 1) Use a SAX parser (XML) - I chose Ruby, and Nokogiri. I started writing the parser, but my initial reaction: how would I map the XML schema to the SAX parser? 2) BioPython - I already have BioSQL/Biopython installed, which literally created my SQL schema for me, and I was able to successfully insert one SwissProt/Uniprot txt file into the database. I'm running it right now (crosses fingers) on the entire 2.1gb. Here is the code I'm running: from Bio import SeqIO from BioSQL import BioSeqDatabase from Bio import SwissProt server = BioSeqDatabase.open_database(driver = "MySQLdb", user = "root", passwd = "", host="localhost", db = "bioseqdb") db = server["uniprot"] iterator = SeqIO.parse(open("/path/to/uniprot_sprot.dat", "r"), "swiss") db.load(iterator) server.commit() Edit: it's now crashing because the transactions are getting locked (since the tables are Innodb) Error Number: 1205 Lock wait timeout exceeded; try restarting transaction. I'm using MySQL version: 5.1.43 Should I switch my database to Postgrelsql ?

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• how to minimize application downtime when updating database and application ORM

  - by yamspog

  We currently run an ecommerce solution for a leisure and travel company. Everytime we have a release, we must bring the ecommerce site down as we update database schema and the data access code. We are using a custom built ORM where each data entity is responsible for their own CRUD operations. This is accomplished by dynamically generating the SQL based on attributes in the data entity. For example, the data entity for an address would be... [tableName="address"] public class address : dataEntity { [column="address1"] public string address1; [column="city"] public string city; } So, if we add a new column to the database, we must update the schema of the database and also update the data entity. As you can expect, the business people are not too happy about this outage as it puts a crimp in their cash-flow. The operations people are not happy as they have to deal with a high-pressure time when database and applications are upgraded. The programmers are upset as they are constantly getting in trouble for the legacy system that they inherited. Do any of you smart people out there have some suggestions?

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• "no inclosing instance error " while getting top term frequencies for document from Lucene index

  - by Julia

  Hello ! I am trying to get the most occurring term frequencies for every particular document in Lucene index. I am trying to set the treshold of top occuring terms that I care about, maybe 20 However, I am getting the "no inclosing instance of type DisplayTermVectors is accessible" when calling Comparator... So to this function I pass vector of every document and max top terms i would like to know protected static Collection getTopTerms(TermFreqVector tfv, int maxTerms){ String[] terms = tfv.getTerms(); int[] tFreqs = tfv.getTermFrequencies(); List result = new ArrayList(terms.length); for (int i = 0; i < tFreqs.length; i++) { TermFrq tf = new TermFrq(terms[i], tFreqs[i]); result.add(tf); } Collections.sort(result, new FreqComparator()); if(maxTerms < result.size()){ result = result.subList(0, maxTerms); } return result; } /Class for objects to hold the term/freq pairs/ static class TermFrq{ private String term; private int freq; public TermFrq(String term,int freq){ this.term = term; this.freq = freq; } public String getTerm(){ return this.term; } public int getFreq(){ return this.freq; } } /*Comparator to compare the objects by the frequency*/ class FreqComparator implements Comparator{ public int compare(Object pair1, Object pair2){ int f1 = ((TermFrq)pair1).getFreq(); int f2 = ((TermFrq)pair2).getFreq(); if(f1 > f2) return 1; else if(f1 < f2) return -1; else return 0; } } Explanations and corrections i will very much appreciate, and also if someone else had experience with term frequency extraction and did it better way, I am opened to all suggestions! Please help!!!! Thanx!

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• Diff/Merge functionality for objects (not files!)

  - by gehho

  I have a collection of objects of the same type, let's call it DataItem. The user can view and edit these items in an editor. It should also be possible to compare and merge different items, i.e. some sort of diff/merge for DataItem instances. The DIFF functionality should compare all (relevant) properties/fields of the items and detect possible differences. The MERGE functionality should then be able to merge two instances by applying selected differences to one of the items. For example (pseudo objects): DataItem1 { DataItem2 { Prop1 = 10 Prop1 = 10 Prop2 = 25 Prop2 = 13 Prop3 = 0 Prop3 = 5 Coll = { 7, 4, 8 } Coll = { 7, 4, 8, 12 } } } Now, the user should be provided with a list of differences (i.e. Prop2, Prop3, and Coll) and he should be able to select which differences he wants to eliminate by assigning the value from one item to the other. He should also be able to choose if he wants to assign the value from DataItem1 to DataItem2 or vice versa. Are there common practices which should be used to implement this functionality? Since the same editor should also provide undo/redo functionality (using the Command pattern), I was thinking about reusing the ICommand implementations because both scenarios basically handle with property assignments, collection changes, and so on... My idea was to create Difference objects with ICommand properties which can be used to perform a merge operation for this specific Difference. Btw: The programming language will be C# with .NET 3.5SP1/4.0. However, I think this is more of a language-independent question. Any design pattern/idea/whatsoever is welcome!

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• xsl:for-each not supported in this context

  - by alexbf

  Hi! I have this XSLT document : <xsl:stylesheet version="1.0" xmlns:mstns="http://www.w3.org/2001/XMLSchema" xmlns="http://www.w3.org/2001/XMLSchema" xmlns:xs="http://www.w3.org/2001/XMLSchema" xmlns:msdata="urn:schemas-microsoft-com:xml-msdata" xmlns:xsl="http://www.w3.org/1999/XSL/Transform"> <xsl:output method="xml" version="1.0" encoding="UTF-8" indent="yes"/> <xsl:template match="/MyDocRootElement"> <xs:schema id="DataSet" targetNamespace="http://www.w3.org/2001/XMLSchema" attributeFormDefault="qualified" elementFormDefault="qualified" > <xs:element name="DataSet" msdata:IsDataSet="true"> <xs:complexType> <xs:choice maxOccurs="unbounded"> <xs:element name="Somename"> </xs:element> <xs:element name="OtherName"> </xs:element> <!-- FOR EACH NOT SUPPORTED? --> <xsl:for-each select="OtherElements/SubElement"> <xs:element name="OtherName"> </xs:element> </xsl:for-each> </xs:choice> </xs:complexType> </xs:element> </xs:schema> </xsl:template> </xsl:stylesheet> I have a validation error saying that the "for-each element is not supported in this context" I am guessing it has something to do with the xs namespace validation. Any ideas on how can I make this work? (Exclude validation?) Thanks Alex

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• Contrary to Python 3.1 Docs, hash(obj) != id(obj). So which is correct?

  - by Don O'Donnell

  The following is from the Python v3.1.2 documentation: From The Python Language Reference Section 3.3.1 Basic Customization: object.__hash__(self) ... User-defined classes have __eq__() and __hash__() methods by default; with them, all objects compare unequal (except with themselves) and x.__hash__() returns id(x). From The Glossary: hashable ... Objects which are instances of user-defined classes are hashable by default; they all compare unequal, and their hash value is their id(). This is true up through version 2.6.5: Python 2.6.5 (r265:79096, Mar 19 2010 21:48:26) ... ... >>> class C(object): pass ... >>> c = C() >>> id(c) 11335856 >>> hash(c) 11335856 But in version 3.1.2: Python 3.1.2 (r312:79149, Mar 21 2010, 00:41:52) ... ... >>> class C: pass ... >>> c = C() >>> id(c) 11893680 >>> hash(c) 743355 So which is it? Should I report a documentation bug or a program bug? And if it's a documentation bug, and the default hash() value for a user class instance is no longer the same as the id() value, then it would be interesting to know what it is or how it is calculated, and why it was changed in version 3.

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• generic binary Search in c#

  - by Pro_Zeck

  Below is my Generic Binary Search it works ok with the intgers type array it finds all the elements in it . But the Problem Arises when i use a string array to find any string data. It runs ok for the first index and last index elements but i cant find the middle elements. Stringarray = new string[] { "b", "a", "ab", "abc", "c" }; public static void BinarySearch<T>(T[] array, T searchFor, Comparer<T> comparer) { int high, low, mid; high = array.Length - 1; low = 0; if (array[0].Equals(searchFor)) Console.WriteLine("Value {0} Found At Index {1}",array[0],0); else if (array[high].Equals(searchFor)) Console.WriteLine("Value {0} Found At Index {1}", array[high], high); else { while (low <= high) { mid = (high + low) / 2; if (comparer.Compare(array[mid], searchFor) == 0) { Console.WriteLine("Value {0} Found At Index {1}", array[mid], mid); break; } else { if (comparer.Compare(searchFor, array[mid]) > 0) high = mid + 1; else low = mid + 1; } } if (low > high) { Console.WriteLine("Value Not Found In the Collection"); } } }

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• Using C# to parse a SOAP Response

  - by Gavin

  I am trying to get the values for faultcode, faultstring, and OrderNumber from the SOAP below <SOAP:Envelope xmlns:SOAP="http://schemas.xmlsoap.org/soap/envelope/"> <SOAP:Body> <faultcode>1234</faultcode> <faultstring>SaveOrder:SetrsOrderMain:Cannot change OrderDate if GLPeriod is closed, new OrderDate is 3/2/2010:Ln:1053</faultstring> <detail> <SOAP:Envelope xmlns:SOAP="http://schemas.xmlsoap.org/soap/envelope/"> <SOAP:Body UserGUID="test"> <m:SaveOrder xmlns:m="http://www.test.com/software/schema/" UserGUID="test"> <Order OrderNumber="1234-1234-123" Caller="" OrderStatus="A" xmlns="http://www.test.com/software/schema/"> Here is my code in C# XDocument doc = XDocument.Load(HttpContext.Current.Server.MapPath("XMLexample.xml")); var errorDetail = new EcourierErrorDetail { FaultCode = from fc in doc.Descendants("faultcode") select fc.Value, FaultString = from fs in c.Descendants("faultstring") select fs.Value, OrderNumber = from o in doc.Descendants("detail").Elements("Order").Attributes("OrderNumber") select o.Value }; return errorDetail; I am able to get the values for both faultcode and faultstring but not the OrderNumber. I am getting "Enumeration yielded no results." Can anyone help? Thanks.

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• How to create a reference tables for collection classes using fluent nhibernate

  - by Akk

  How can i create a 3 table schema from the following model classes. public class Product { public int Id {get; set;} public string Name {get; set;} public IList<Photo> Photos {get; set;} } public class Photo { public int Id {get; set;} public string Path {get; set;} } I want to create the following table structure in the database: Product ------- Id Name ProductPhotos ------------- ProductId (FK Products.Id) PhotoId (FK Photos.Id) Photos ------ Id Path How i can express the above Database Schema using Fluent NHibernate? I could only manage the following the Mapping but this does not get me the 3rd Photo ref table. public class ProductMap : ClassMap<Product> { public CityMap() { Id(x => x.Id); Map(x => x.Name); Table("Products"); HasMany(x => x.Photos).Table("ProductPhotos").KeyColumn("ProductId"); } }

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• "end()" iterator for back inserters?

  - by Thanatos

  For iterators such as those returned from std::back_inserter(), is there something that can be used as an "end" iterator? This seems a little nonsensical at first, but I have an API which is: template<typename InputIterator, typename OutputIterator> void foo( InputIterator input_begin, InputIterator input_end, OutputIterator output_begin, OutputIterator output_end ); foo performs some operation on the input sequence, generating an output sequence. (Who's length is known to foo but may or may not be equal to the input sequence's length.) The taking of the output_end parameter is the odd part: std::copy doesn't do this, for example, and assumes you're not going to pass it garbage. foo does it to provide range checking: if you pass a range too small, it throws an exception, in the name of defensive programming. (Instead of potentially overwriting random bits in memory.) Now, say I want to pass foo a back inserter, specifically one from a std::vector which has no limit outside of memory constraints. I still need a "end" iterator - in this case, something that will never compare equal. (Or, if I had a std::vector but with a restriction on length, perhaps it might sometimes compare equal?) How do I go about doing this? I do have the ability to change foo's API - is it better to not check the range, and instead provide an alternate means to get the required output range? (Which would be needed anyways for raw arrays, but not required for back inserters into a vector.) This would seem less robust, but I'm struggling to make the "robust" (above) work.

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• When to save a mongoose model

  - by kentcdodds

  This is an architectural question. I have models like this: var foo = new mongoose.Schema({ name: String, bars: [{type: ObjectId, ref: 'Bar'}] }); var FooModel = mongoose.model('Foo', foo); var bar = new mongoose.Schema({ foobar: String }); var BarModel = mongoose.model('Bar', bar); Then I want to implement a convenience method like this: BarModel.methods.addFoo = function(foo) { foo.bars = foo.bars || []; // Side note, is this something I should check here? foo.bars.push(this.id); // Here's the line I'm wondering about... Should I include the line below? foo.save(); } The biggest con I see about this is that if I did include foo.save() then I should pass in a callback to addFoo so I avoid issues with the async operation. I'm thinking this is not preferable. But I also think it would be nice to include because addFoo hasn't really "addedFoo" until it's been saved... Am I breaking any design best practices doing it either way?

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• Phonegap: Will my mobile app 'feel' faster or slower once ported to phonegap?

  - by user15872

  So I'm designing everything in mobile Safari and I know that phonegap is essentially a stripped webview but... Question: Will my application will run better in phonegap? (revised below) a)I imagine my navigation and core app will load faster as the scripts and images are on the hard drive. Is this True? b)I assume since they've been working on it for 2 years now that they may have made some optimizations to make it quicker than just an average safari window. Is this true? (Assuming both html5/js/css code bases are pretty much the same and app is running on iOS.) Update: Sorry, I meant to compare apples to slightly different apples. Question 1 revised: Will my app see any performance benefits running with in a phonegap environment vs standard mobile safari? (compare mobile - to mobile) 1b) In what ways, other than loading time has phonegap optimized performance over standard mobile safari? Follow ups: 1) Are there any pitfalls, other than large libraries, that may cause phonegap to suffer a serious performance hit vs stand mobile safari? 2) Can I mix native and webview rendering? (i.e the top half of my app is rendered in with html/css/js and the bottom half native)

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• Performance issue finding weekdays over a given period

  - by Oysio

  I have some methods that return the number of weekdays between two given dates. Since calling these methods become very expensive to call when the two dates lie years apart, I'm wondering how these methods could be refactored in a more efficient way. The returned result is correct but I feel that the iphone processor is struggling to keep up and consequently freezes up the application when I would call these methods over a period of say 10years. Any suggestions ? //daysList contains all weekdays that need to be found between the two dates -(NSInteger) numberOfWeekdaysFromDaysList:(NSMutableArray*) daysList startingFromDate:(NSDate*)startDate toDate:(NSDate*)endDate { NSInteger retNumdays = 0; for (Day *dayObject in [daysList objectEnumerator]) { if ([dayObject isChecked]) { retNumdays += [self numberOfWeekday:[dayObject weekdayNr] startingFromDate:startDate toDate:endDate]; } } return retNumdays; } -(NSInteger) numberOfWeekday:(NSInteger)day startingFromDate:(NSDate*)startDate toDate:(NSDate*)endDate { NSInteger numWeekdays = 0; NSDate *nextDate = startDate; NSComparisonResult result = [endDate compare:nextDate]; //Do while nextDate is in the past while (result == NSOrderedDescending || result == NSOrderedSame) { if ([NSDate weekdayFromDate:nextDate] == day) { numWeekdays++; } nextDate = [nextDate dateByAddingDays:1]; result = [endDate compare:nextDate]; } return numWeekdays; }

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• C# SQL Data Adapter Fill on existing typed Dataset

  - by René

  I have an option to choose between local based data storing (xml file) or SQL Server based. I already created a long time ago a typed dataset for my application to save data local in the xml file. Now, I have a bool that changes between Server based version and local version. If true my application get the data from the SQL Server. I'm not sure but It seems that Sql Adapter's Fill Method can't fill the Data in my existing schema SqlCommand cmd = new SqlCommand("Select * FROM dbo.Categories WHERE CatUserId = 1", _connection); cmd.CommandType = CommandType.Text; _sqlAdapter = new SqlDataAdapter(cmd); _sqlAdapter.TableMappings.Add("Categories", "dbo.Categories"); _sqlAdapter.Fill(Program.Dataset); This should fill my data from dbo.Categories to Categories (in my local, typed dataset). but it doesn't. It creates a new table with the name "Table". It looks like it can't handle the existing schema. I can't figure it out. Where is the problem? btw. of course the database request I do isn't very useful that way. It's just a simplified version for testing...

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• Heroku only initializes some of my models.

  - by JayX

  So I ran heroku db:push And it returned Sending schema Schema: 100% |==========================================| Time: 00:00:08 Sending indexes schema_migrat: 100% |==========================================| Time: 00:00:00 projects: 100% |==========================================| Time: 00:00:00 tasks: 100% |==========================================| Time: 00:00:00 users: 100% |==========================================| Time: 00:00:00 Sending data 8 tables, 70,551 records groups: 100% |==========================================| Time: 00:00:00 schema_migrat: 100% |==========================================| Time: 00:00:00 projects: 100% |==========================================| Time: 00:00:00 tasks: 100% |==========================================| Time: 00:00:02 authenticatio: 100% |==========================================| Time: 00:00:00 articles: 100% |==========================================| Time: 00:08:27 users: 100% |==========================================| Time: 00:00:00 topics: 100% |==========================================| Time: 00:01:22 Resetting sequences And when I went to heroku console This worked >> Task => Task(id: integer, topic: string, content: string, This worked >> User => User(id: integer, name: string, email: string, But the rest only returned something like >> Project NameError: uninitialized constant Project /home/heroku_rack/lib/console.rb:150 /home/heroku_rack/lib/console.rb:150:in `call' /home/heroku_rack/lib/console.rb:28:in `call' >> Authentication NameError: uninitialized constant Authentication /home/heroku_rack/lib/console.rb:150 /home/heroku_rack/lib/console.rb:150:in `call' update 1: And when I typed >> ActiveRecord::Base.connection.tables it returned => ["projects", "groups", "tasks", "topics", "articles", "schema_migrations", "authentications", "users"] Using heroku's SQL console plugin I got SQL> show tables +-------------------+ | table_name | +-------------------+ | authentications | | topics | | groups | | projects | | schema_migrations | | tasks | | articles | | users | +-------------------+ So I think they are existing in heroku's database already. There is probably something wrong with rack db:migrate update 2: I ran rack db:migrate locally in both production and development modes and nothing wrong happened. But when I ran it on heroku it only returned: $ heroku rake db:migrate (in /disk1/home/slugs/389817_1c16250_4bf2-f9c9517b-bdbd-49d9-8e5a-a87111d3558e/mnt) $ Also, I am using sqlite3 update 3: so I opened up heroku console and typed in the following command class Authentication < ActiveRecord::Base;end Amazingly I was able to call Authentication class, but once I exited, nothing was changed.

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• Comparing objects and inheritance

  - by ereOn

  Hi, In my program I have the following class hierarchy: class Base // Base is an abstract class { }; class A : public Base { }; class B : public Base { }; I would like to do the following: foo(const Base& one, const Base& two) { if (one == two) { // Do something } else { // Do something else } } I have issues regarding the operator==() here. Of course comparing an instance A and an instance of B makes no sense but comparing two instances of Base should be possible. (You can't compare a Dog and a Cat however you can compare two Animals) I would like the following results: A == B = false A == A = true or false, depending on the effective value of the two instances B == B = true or false, depending on the effective value of the two instances My question is: is this a good design/idea ? Is this even possible ? What functions should I write/overload ? My apologies if the question is obviously stupid or easy, I have some serious fever right now and my thinking abilities are somewhat limited :/ Thank you.

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• Is there a way to create subdatabases as a kind of subfolders in sql server?

  - by user193655

  I am creating an application where there is main DB and where other data is stored in secondary databases. The secondary databases follow a "plugin" approach. I use SQL Server. A simple installation of the application will just have the mainDB, while as an option one can activate more "plug-ins" and for every plug-in there will be a new database. Now why I made this choice is because I have to work with an exisiting legacy system and this is the smartest thing I could figure to implement the plugin system. MainDB and Plugins DB have exactly the same schema (basically Plugins DB have some "special content", some important data that one can use as a kind of template - think to a letter template for example - in the application). Plugin DBs are so used in readonly mode, they are "repository of content". The "smart" thing is that the main application can also be used by "plugin writers", they just write a DB inserting content, and by making a backup of the database they creaetd a potential plugin (this is why all DBs has the same schema). Those plugins DB are downloaded from internet as there is a content upgrade available, every time the full PlugIn DB is destroyed and a new one with the same name is creaetd. This is for simplicity and even because the size of this DBs is generally small. Now this works, anyway I would prefer to organize the DBs in a kind of Tree structure, so that I can force the PlugIn DBs to be "sub-DBs" of the main application DB. As a workaround I am thinking of using naming rules, like: ApplicationDB (for the main application DB) ApplicationDB_PlugIn_N (for the N-th plugin DB) When I search for plugin 1 I try to connect to ApplicationDB_PlugIn_1, if I don't find the DB i raise an error. This situation can happen for example if som DBA renamed ApplicationDB_Plugin_1. So since those Plugin DBs are really dependant on ApplicationDB only I was trying to "do the subfolder trick". Can anyone suggest a way to do this? Can you comment on this self-made plugin approach I decribed above?

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• How To Block The UserName After 3 Invalid Password Attempts IN ASP.NET

  - by shihab

  I used the following code for checking user name and password. and I want ti block the user name after 3 invalid password attempt. what should I add in my codeing MD5CryptoServiceProvider md5hasher = new MD5CryptoServiceProvider(); Byte[] hashedDataBytes; UTF8Encoding encoder = new UTF8Encoding(); hashedDataBytes = md5hasher.ComputeHash(encoder.GetBytes(TextBox3.Text)); StringBuilder hex = new StringBuilder(hashedDataBytes.Length * 2); foreach (Byte b in hashedDataBytes) { hex.AppendFormat("{0:x2}", b); } string hash = hex.ToString(); SqlConnection con = new SqlConnection("Data Source=Shihab-PC;Initial Catalog=test;User ID=SOMETHING;Password=SOMETHINGELSE"); SqlDataAdapter ad = new SqlDataAdapter("select password from Users where UserId='" + TextBox4.Text + "'", con); DataSet ds = new DataSet(); ad.Fill(ds, "Users"); SqlDataAdapter ad2 = new SqlDataAdapter("select UserId from Users ", con); DataSet ds2 = new DataSet(); ad2.Fill(ds2, "Users"); Session["id"] = TextBox4.Text.ToString(); if ((string.Compare((ds.Tables["Users"].Rows[0][0].ToString()), hash)) == 0) { if (string.Compare(TextBox4.Text, (ds2.Tables["Users"].Rows[0][0].ToString())) == 0) { Response.Redirect("actioncust.aspx"); } else { Response.Redirect("actioncust.aspx"); } } else { Label2.Text = "Invalid Login"; } con.Close(); }

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• Timestamps and Intervals: NUMTOYMINTERVAL SYSTDATE CALCULATION SQL QUERY

  - by MeachamRob

  I am working on a homework problem, I'm close but need some help with a data conversion I think. Or sysdate - start_date calculation The question is: Using the EX schema, write a SELECT statement that retrieves the date_id and start_date from the Date_Sample table (format below), followed by a column named Years_and_Months_Since_Start that uses an interval function to retrieve the number of years and months that have elapsed between the start_date and the sysdate. (Your values will vary based on the date you do this lab.) Display only the records with start dates having the month and day equal to Feb 28 (of any year). DATE_ID START_DATE YEARS_AND_MONTHS_SINCE_START 2 Sunday , February 28, 1999 13-8 4 Monday , February 28, 2005 7-8 5 Tuesday , February 28, 2006 6-8 Our EX schema that refers to this question is simply a Date_Sample Table with two columns: DATE_ID NUMBER NOT Null START_DATE DATE I Have written this code: SELECT date_id, TO_CHAR(start_date, 'Day, MONTH DD, YYYY') AS start_date , NUMTOYMINTERVAL((SYSDATE - start_date), 'YEAR') AS years_and_months_since_start FROM date_sample WHERE TO_CHAR(start_date, 'MM/DD') = '02/28'; But my Years and months since start column is not working properly. It's getting very high numbers for years and months when the date calculated is from 1999-ish. ie, it should be 13-8 and I'm getting 5027-2 so I know it's not correct. I used NUMTOYMINTERVAL, which should be correct, but don't think the sysdate-start_date is working. Data Type for start_date is simply date. I tried ROUND but maybe need some help to get it right. Something is wrong with my calculation and trying to figure out how to get the correct interval there. Not sure if I have provided enough information to everyone but I will let you know if I figure it out before you do. It's a question from Murach's Oracle and SQL/PL book, chapter 17 if anyone else is trying to learn that chapter. Page 559.

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• How do I introspect on a SQL Server?

  - by MetaHyperBolic

  I have a server with a vendor application which is heavily database-reliant. I need to make some minor changes to the data in a few tables in the database in an automated fashion. Just INSERTs and UPDATEs, nothing fancy. Vendors being vendors, I can never be quite sure when they change the schema of a database during upgrade. To that end, how do I ask the SQL server, in some scriptable fashion, "Hey, does this table still exist? Yeah, cool, okay, but does it have this column? What's the data type and size on that? Is it nullable? Could you give me a list of tables? In this table, could you give me a list of columns? Any primary keys there?" I do not need to do this for the whole schema, only part of it, just a quick check of the database before I launch into things. We have Microsoft SQL Server 2005 on it currently, but it might easily move to Microsoft SQL Server 2008. I am probably not using the correct terminology when searching. I do know that ORM is not only too much overhead for this sort of thing, but also that I have no chance of pitching it to my coworkers.

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