Wednesday, 21 November 2012

Windows 8 Pro on an early 2009 iMac 21.5 (Core 2 Duo)

A couple of weeks back I thought I'd have a go writing a Windows Store App.  To do this requires Windows 8.  At the time I was running Windows 7 Home Premium on an early 2009 iMac 21.5 (Core 2 Duo).  This had been installed using Boot Camp including install Boot Camp assistant and the drivers supplied by Apple.

To upgrade to Windows 8 I wanted to avoid a re-installation of all my apps. and data etc so I went with an in place upgrade.  This all seemed to work properly and soon I was running Windows 8 and could access the Windows Store App templates from Visual Studio.  However, soon after Windows 8 kept crashing, well freezing.  It got to the point that after every reboot I'd be lucky to get 5 minutes of up time between each freeze.

Given that Apple haven't provided Windows 8 drivers yet this wasn't exactly a surprise.  I decided to try and work around this by rebooting to OS X and using VMWare Fusion to access the Boot Camp partition.  Whilst rebooting in OS X I managed to corrupt the Windows installation.  I use a non-Apple wireless keyboard (as I need the insert, delete, home & end plus the easily accessible cursor keys for VS development) so holding down Alt to select the OS to boot into didn't work.  When I realized it was going back into Windows I just turned the machine off.  After a couple of times the Windows installation was toast!  To get back to the point of trying Fusion I had to do a fresh Windows install.  In this case installing a minimal Windows 7 installation: just enough to allow the download of Windows 8.  I then installed Windows 8 using the preserve nothing option.

Having now gone through the steps I wanted to avoid I decided to give the new installation a go via direct boot, i.e. no Fusion.  That was two weeks ago.  Since then I've re-installed all the apps. and my personal data and (fingers crossed) haven't had a single crash.  As the freezes were usually happening during some graphical operation e.g. a status bar updating I assumed the fault probably lay with the video drivers.  I didn't install Boot Camp assistant and in particular the Windows 7 drivers from OS X disc.  Well, I did install one.  After a while I noticed I wasn't getting any sound even though all the audio drivers and hardware claimed they were happy.  Eventually I installed by the Cirrus Logic driver which made the speakers work. I haven't gone anywhere near the NVIDIA drivers.

So, the whole point of this post is for those who run Windows via Boot Camp on early iMacs and want to run Windows 8 then perhaps a fresh install (or maybe uninstall the Boot Camp supplied drivers prior to upgrade) is probably the way to go.

Friday, 3 August 2012

Specifying the directory to create SQL CE databases when using Entity Framework

In the last few posts I've been describing how to create instances of SQLCE in order to perform automated Integration Testing using NUnit and accessing the dB using Entity Framework.  I covered creating the dB using both Entity Framework and the SQL CE classes.  In particular I wanted control over the directory the dB was created in but I didn't want to tie to a specific location rather let it use the current working directory.

Using the Entity Framework's DbContext constructor that takes the name of a connection string or database name it's suddenly very easy to end up NOT creating the dB you expected where you expected it to be.  This post shows how to avoid these.  Generally speaking the use of the DbContext constructor that takes a Connection String should be avoided unless the name of a connection string from the .config file is being specified.

Example 1 - Using the SqlCeEngine class
1:  const string DB_NAME = "test1.sdf";  
2:  const string DB_PATH = @".\" + DB_NAME; // Use ".\" for CWD or a specific path  
3:  const string CONNECTION_STRING = "data source=" + DB_PATH;  
5:  using (var eng = new SqlCeEngine(CONNECTION_STRING))  
6:  {  
7:    eng.CreateDatabase();  
8:  }  
10:  using (var conn = new SqlCeConnection(CONNECTION_STRING))  
11:  {  
12:    conn.Open(); // do stuff with db...  
13:  }  

The important thing to note is that the constructor for SqlCeEngine that takes an argument requires a Connection String, i.e. a string containing the "data source=...".  Just specifying the dB path is not sufficient.  To specify a specific directory  include the absolute or relative path.  To specify the current working directory, e.g. bin\debug then just use ".\".

Example 2 - Using DbContext (doesn't work)
1:  using (var ctx = new DbContext("test2.sdf"))  
2:  {  
3:    ctx.Database.Create();  
4:  }  

This code appears to work but doesn't create an instance of an SQL CE dB as desired.  Instead it creates a localDB instance in the user's home directory.  In my case: C:\Users\Pete\._test.sdf.mdf (& corresponding log file).  This is not really surprising as Entity Framework had no way of knowing that a SQL CE dB should be created.

Example 3 - Using DbContext (does work)
1:  Database.DefaultConnectionFactory =  
2:    new SqlCeConnectionFactory(  
3:      "System.Data.SqlServerCe.4.0",  
4:      @".\", "");  
6:  using (var ctx = new DbContext("test2.sdf"))  
7:  {  
8:    ctx.Database.Create();  
9:    // do stuff with ctx...  
10:  }  

The difference between the last and this example is changing the default type of dB that EF should create.  As shown this is done by installing a different factory.

The 3rd parameter to SqlCeConnectionFactory is the directory that the dB should be created in.  Just like the first example specifying ".\" means the current working directory and specifying an absolute path to a directory will lead to them being created there.

NOTE: As per the post Integration Testing with NUnit and Entity Framework be aware that creating a dB using the Entity Framework results in the additional table '_MigrationHistory' being created which EF uses to keep the model and dB synchronized.

NOTE1: Whereas SqlCeEngine is a SQL CE class from the System.Data.SqlServerCe assembly, SqlCeConnectionFactory appears to be part of the System.Data.Entity assembly which is part of the Entity Framework.

In the above example the string passed to DbContext can be a name (of a connection string from the .config file) or a connection string.  In this case passing the name of the db, i.e. test2.sdf is equivalent to passing "data source=test2.sdf", well more or less.  If the '.sdf' suffix is omitted with "data source" then the resultant dB is called test2 but if just test2 is passed then the resulting dB will be called test2.sdf.

Example 4 - Using DbContext and the .config file
1:  using (var ctx = new DbContext("test5"))  
2:  {  
3:    ctx.Database.Create();  
4:  }  

App or Web .config
1:  <connectionStrings>  
2:    <add name="test5"  
3:      providerName="System.Data.SqlServerCe.4.0"  
4:      connectionString="Data Source=test5.sdf"/>  
5:  </connectionStrings>  

This time no factory is specified but the argument to DbContext is the name of a Connection String in the .config file.  As can be seen this contains similar information to that in the factory method enabling EF to create a dB of the correct type.

To use these the instances of these databases rather than calling the create method on the context just use the context directly or more likely in the case of EF a derived context which brings us to one last example.

Example 5 - Using a derived context and .config file
1:  public class TestCtx : DbContext  
2:  {      
3:  }  
4:  using (var ctx = new TestCtx())  
5:  {  
6:    ctx.Database.Create();  
7:  }    

App or Web .config
1:  <connectionStrings>  
2:    <add name="TestCtx"  
3:      providerName="System.Data.SqlServerCe.4.0"  
4:      connectionString="Data Source=test6.sdf"/>  
5:  </connectionStrings>  

If a derived context is created which will almost certainly be the case then if an instance of this is created and a dB created then EF will look for a Connection String in the .config file that has the same name as the context and take the information from there.

Thursday, 2 August 2012

Integration Testing with NUnit and Entity Framework

This post gives a quick introduction into creating SQL CE dBs for performing Integration Tests using NUnit.

In the previous post Using NUnit and Entity Framework DbContext to programmatically create SQL Server CE databases and specify the databse directory a basic way was shown to how to create a new dB (using Entity Framework's DbContext) programmtically.  This was used to generate a new dB for a test hosted by NUnit.

The subsequent post Generating a SQL Server CE database schema from a SQL Server database using Entity Framework showed how to generate a SQL CE dB schema from an existing SQL Server database.

This post ties theprevious ones together.  As mentioned in the first post the reason for this is an attempt at what amounts to Integration Testing using NUnit.  I'm currently building a Repository and Unit Of Work abstraction on top of Entity Framework which will allow the isolation of the dB code (in fact it will isolate and abstract away most forms of data storage).  This means any business logic can be tested with a test-double that implements the Repository and UnitOfWork interfaces; which is straight forward Unit Testing.  The Integration Testing is to verify that the Repository and Unit Of Work implementations work correctly.

The rest of the post isn't focused on these two patterns; though it may mention them.  Instead it documents my further experience of using NUnit to writes tests that interact with dB via Entity Framework.  The premise for this is that a dB already exists.

As such the approach to using Entity Framework is a hybrid of Database First and Code First in that the dB schema exists and needs be maintained outside of EF and also that EF should not generate model classes, i.e. allowing the use of Code First POCOs.  This is possible as the POCOs can be defined, a connection made to dB and then the two are conflated via an EF DbContext.  It then seems that EF creates the model on the fly (internally compiles it) and as long as the POCO types map to the dB types then it all works as if by magic!

The advantage of doing it this way is that the existing dB is SQL Express based but for the Integration Testing a new dB can be created when needed, potentially one per test.  In order to keep the test dBs isolated from the real dB SQL Server Compact Edition (SQL Server CE V4) was used.  Therefore the requirement was for the EF code to be able to work with SQL Express and SQL CE with the primary definition of the schema taken from SQL Express.  It's not possible to use exactly the same schema as SQL CE only has a subset of the data-types provides by SQL CE.  However, the process described in the post 
Generating a SQL Server CE database schema from a SQL Server database using Entity Framework showed how to create semantically equivalent SQL.

From this point onwards it's assumed that an SQL file to create the dB has been generated.  Now create a new C# class library project and using the NUGet add Entity Framework, NUnit and SQL CE 4.0.  All my work has been with EF 4.3.1.  Following this drag the Model1.edmx.sqlce file from the project used to generate to new project.  You may wish to rename it, e.g. to test.sqlce.

Creating the database

The post Generating a SQL Server CE database schema from a SQL Server database using Entity Framework showed how to create a new CE dB per-test using the EF DbContext to do the hard work.  A different approach is now taken as the problem with creating a dB using DbContext is that in addition to creating any specified tables and indices etc. it also creates an additional table called '__MigrationHistory' which contains a description of the EF model used to create the dB.  The description of the problem caused by this will be delayed until the "Why DbContext is no longer used to create the database" section.  Suffice to say for the present using the new mechanism avoids the creation of this table.

The code below is the beginnings of a test class.  It is assumed all the tests need a fresh copy of the dB hence the creation is performed in the Setup method.  All this code does is create a SQL CE dB and then
creates the schema.

1:  [TestFixture]  
2:  public class SimpleTests  
3:  {  
4:   const string DB_NAME = "test.sdf";  
5:   const string DB_PATH = @".\" + DB_NAME;  
6:   const string CONNECTION_STRING = "data source=" + DB_PATH;  
7:   [SetUp]  
8:   public void Setup()  
9:   {  
10:    DeleteDb();  
11:    using (var eng = new SqlCeEngine(CONNECTION_STRING))  
12:     eng.CreateDatabase();  
13:    using (var conn = new SqlCeConnection(CONNECTION_STRING))  
14:    {  
15:     conn.Open();  
16:      string sql=ReadSQLFromFile(@"C:\Users\Pete\work\Jub\EFTests\Test.sqlce");  
17:      string[] sqlCmds = sql.Split(new string[] { "GO" }, int.MaxValue, StringSplitOptions.RemoveEmptyEntries);  
18:      foreach (string sqlCmd in sqlCmds)  
19:       try  
20:       {  
21:        var cmd = conn.CreateCommand();  
23:        cmd.CommandText = sqlCmd;  
24:        cmd.ExecuteNonQuery();  
25:       }  
26:       catch (Exception e)  
27:       {  
28:        Console.Error.WriteLine("{0}:{1}", e.Message, sqlCmd);  
29:        throw;  
30:       }  
31:    }  
32:   }  
33:   public void DeleteDb()  
34:   {  
35:    if (File.Exists(DB_PATH))  
36:     File.Delete(DB_PATH);  
37:   }  
38:   private string ReadSQLFromFile(string sqlFilePath)  
39:   {  
40:    using (TextReader r = new StreamReader(sqlFilePath))  
41:    {  
42:     return r.ReadToEnd();  
43:    }  
44:   }  
45:  }  
The dB file (Test.sdf) will be created in the current working directory.  As the test assembly is located in <project>\bin\debug which is where the NUnit test runner picks up the DLL from this directory this is where it is created.  If a specific directory is required then the '.\' can be replaced with the required path.

The Setup method is marked with NUnit's SetUp attribute meaning it will be invoked on a per-test basis creating a new dB instance for each test.  The DeleteDb method could be marked with [TearDown] attribute but at the moment any previous dB is deleted before creating a new one.  It would be fine to do both as a belt and braces approach.  The reason I didn't make it the TearDown method is so that I could inspect the dB following a test if needed.

SQL CE does not support batch execution of SQL scripts which is where it gets interesting as the SQL generated previously is in batch form.  The code reads the entire file into a string and determines each individual statement by splitting string on the 'GO' command that separates each SQL command.

To help understand the SQL the following is the diagram of the dB I'm working with.  All fields are strings except for the Ids which are numeric.
Each of these commands is then executed.  The previously generated SQL (the SQL for the dB I'm working with is below) will not work completely out of the box.  The ALTER and DROP statements at the beginning don't apply as the schema is being applied to an empty dB, these should be removed.  Interestingly the schema generation step for my dB seems to miss out a 'GO' between the penultimate and ultimate statement.  I had to add one by hand.  Finally, the comments at the end prove a problem as there is no terminating 'GO'.  Removing these fixes the problem.  In the code above the exception handler re-throws the exception after writing out the details.  For everything to proceed the SQL needs modifying to execute perfectly.  If the re-throw is removed then the code will tolerate individual command failures which in this context really just amount to warnings.

NOTE: Text highlighted in red has been removed and text in blue added.

-- --------------------------------------------------
-- Entity Designer DDL Script for SQL Server Compact Edition
-- --------------------------------------------------
-- Date Created: 07/29/2012 12:28:35
-- Generated from EDMX file: C:\Users\Pete\work\Jub\DummyWebApplicationToGenerateSQLServerCE4Script\Model1.edmx
-- --------------------------------------------------

-- --------------------------------------------------
-- Dropping existing FOREIGN KEY constraints
-- NOTE: if the constraint does not exist, an ignorable error will be reported.
-- --------------------------------------------------

    ALTER TABLE [RepComments] DROP CONSTRAINT [FK_RepComments_Reps];

-- --------------------------------------------------
-- Dropping existing tables
-- NOTE: if the table does not exist, an ignorable error will be reported.
-- --------------------------------------------------

    DROP TABLE [RepComments];
    DROP TABLE [Reps];
    DROP TABLE [Roads];

-- --------------------------------------------------
-- Creating all tables
-- --------------------------------------------------

-- Creating table 'RepComments'
CREATE TABLE [RepComments] (
    [CommentId] int IDENTITY(1,1) NOT NULL,
    [RepId] int  NOT NULL,
    [Comment] ntext  NOT NULL

-- Creating table 'Reps'
    [RepId] int IDENTITY(1,1) NOT NULL,
    [RepName] nvarchar(50)  NOT NULL,
    [RoadName] nvarchar(256)  NOT NULL,
    [HouseNumberOrName] nvarchar(50)  NOT NULL,
    [ContactTelNumber] nvarchar(20)  NOT NULL,
    [Email] nvarchar(50)  NULL

-- Creating table 'Roads'
    [Name] nvarchar(256)  NOT NULL

-- --------------------------------------------------
-- Creating all PRIMARY KEY constraints
-- --------------------------------------------------

-- Creating primary key on [CommentId] in table 'RepComments'
ALTER TABLE [RepComments]
    PRIMARY KEY ([CommentId] );

-- Creating primary key on [RepId] in table 'Reps'
    PRIMARY KEY ([RepId] );

-- Creating primary key on [Name] in table 'Roads'
    PRIMARY KEY ([Name] );

-- --------------------------------------------------
-- Creating all FOREIGN KEY constraints
-- --------------------------------------------------

-- Creating foreign key on [RepId] in table 'RepComments'
ALTER TABLE [RepComments]
ADD CONSTRAINT [FK_RepComments_Reps]
    FOREIGN KEY ([RepId])
-- Creating non-clustered index for FOREIGN KEY 'FK_RepComments_Reps'
CREATE INDEX [IX_FK_RepComments_Reps]
ON [RepComments]

-- --------------------------------------------------
-- Script has ended
-- --------------------------------------------------

Getting the SQL into a state where it will run flawlessly is a little bit of a hassle but given the number of times it will be used subsequently it's job a big job, well for a small dB anyway.  To verify that your dB has been created as needed an quick and easy way to test is to comment out the call to DeleteDb() and after a test has run open to the dB using Server Explorer within VS, i.e.

Using the dB in a test

Now that a fresh dB will be created for each test it's time to look at simple test:

1:  [Test]  
2:  public void TestOne()  
3:  {  
4:   using (var conn = new SqlCeConnection(CONNECTION_STRING))  
5:    using (var ctx = new TestCtx(conn))  
6:    {  
7:     ctx.Roads.Add(new Road() { Name = "Test" });  
8:     ctx.SaveChanges();  
9:     Assert.That(1, Is.EqualTo(ctx.Roads.Count()));  
10:   }  
11:  }  
Road in this case is defined as:

1:  class Road  
2:  {  
3:   [Key]  
4:   public string Name { get; set; }  
5:  }  

The first thing to note is that EF is not used to form the connection to the dB, instead one is made using the SqlCe specific classes.  Attempting to get EF to connect to a specific dB instance when not referring to a named connection strings in the .config file is a bit of an art (I may write another entry about this).  However, EF is quite happy to work with an existing connection.  This makes for a good separation of responsibilities in the code where EF manages the interactions with the dB but the control of the connection is elsewhere.

NOTE: It is likely that each test will require a connection and a context hence rather it might make more sense to move the creation of the SqlCeConnection and the context (TestCtx in this case) to a SetUp method and as these resources need disposing of adding a TearDown method to do that.  TestCtx could also be modified to pass true to the DbContext constructor to give ownership of the connection to the context so that it will dispose of it then context is disposed off.

I would have preferred to avoid having to defined a specific derived context and instead use DbContext directory, e.g.
1:  [Test]  
2:  public void TesTwo()  
3:  {  
4:   using (var conn = new SqlCeConnection(CONNECTION_STRING))  
5:    using (var ctx = new DbContext(conn, false))  
6:    {  
7:     ctx.Set<Road>().Add(new Road() { Name = "Test" });  
8:     ctx.SaveChanges();  
9:     Assert.That(1, Is.EqualTo(ctx.Set<Road>().Count()));  
10:    }  
11:  }  

However when SaveChanges() is called the following exception is thrown:

System.InvalidOperationException : The entity type Road is not part of the model for the current context.

This is because EF knows nothing about the Road type.  When a derived context is created for the first time I think EF performs reflection on any properties that expose DbSet.  These are the types that form the Model.  Another option is to create the model, optionally compile it and then pass it to an instance of DbContext.  This way involves a lot less code.

That's it.  The final section is just footnote about the move away from using EF to create the dB.

Why DbContext is no longer used to create the database

As mentioned creating the dB using:
1:  using (var ctx = new DbContext("bar.sdf"))  
2:  {  
3:   ctx.Database.Create();  
4:   // create schema etc.  
5:  }  
causes the '__MigrationHistory' table to be created.  Assuming this method was used, later on when TestCtx was used top open the dB and perform an operation the following exception would be thrown:

System.InvalidOperationException : The model backing the 'DbContext' context has changed since the database was created. Consider using Code First Migrations to update the database (
This is because the context used to create the model was a raw DbContext (as per the previous post) whereas the dB was accessed via the TestCtx.  If the context used to create the dB is also changed to TestCtx then this problem goes away.
However, given the original dB is not intended to be created nor be maintained (code migrations) by EF then using the non-context/EF approach to dB completely removes EF from the picture.

Wednesday, 27 June 2012

Generating a SQL Server CE database schema from a SQL Server database using Entity Framework

In a previous entry I described how to programmatically create (& destroy) a SQL CE dB for integration testing using NUnit.  Since getting that working I ran into a couple of other problems which I've more or less solved so I thought I'd write those up.  To begin with though this is a prequel post describing how to obtain the SQL script to create the SQL CE dB.

If you happen to be working exclusively with CE then you'll already have your schema file.  In my case I'm using SQLExpress and as this is experimental work I created my dB by hand.  However, using the EF it's pretty easy to obtain the schema and have the EF wizard generate the CE schema.  This is important as there are differences in the dialect of SQL used by SQL Express and SQL CE and its easier to have a tool handle those, though it doesn't do all of them.

The basic flow is to generate an EF model (EDMX) file from the existing SQL Express database and then use the 'Generate database from model' functionality.  It is at this point that the target SQL dB can be chosen, i.e. SQL Server, SQL Server CE or some others.

To create a model requires adding a 'New Item' of type 'ADO.Net Entity Data Model' to a VS project so first a new dummy project needs creating.  This is where it gets a little complicated as not any type of project will do.  I'm working with CE 4 and require a schema for that version of the dB (though creating one for 3.5 works but I like to things as close to ideal as possible).  Due to this constraint it is necessary to chose a Web type project as for some reason the VS2010 integration provided by EF only supports the generation of CE 4 dBs for Web projects.  If a simple C# Windows Console project is selected then you're limited to CE 3.5.  Thus the simplest project type is the 'ASP.Net Empty Web Application' as shown below.

Having done this, next add a new item of type ADO.Net Entity Data Model as below. NOTE: The project will have to reference the Entity Framework assemblies.  The easiest way to do this (& the one most people are probably using) is to use the NuGet package.

Then follow the wizard.

Selecting "Generate from database".

Choose your SQLExpress (or SQL Server) dB but uncheck the "Save entity connection settings in Web.Config as:" as we're converting to SQLCE so want to minimize anything related to other types of SQL Server.

Finally select the SQL elements you require.  In this example only the existing tables were selected.  As this is generating the EF model from an existing database no SQL file is generated just the model for which the diagram is shown, i.e.

The next phase is to generate the SQL from the model (which was generated from the hand crafted db) but to make sure the SQL that's generated is compliant with SQL CE.

To generate the schema right click and select "Generate model from database..."

This brings up the "Generate database" wizard which is very similar to the previously used "Entity Data Model" wizard used to create the model.  From here choose the "New Connection" option which pops up another set of dialogs.  On the first choose the type of data source as "Microsoft SQL Server Compact 4.0".

Clicking on continue then leads to the next dialog where you need to create a dB.

Ok-ing this leads back to the "Generate database wizard".

This time check the "Save entity connection settings in Web.Config" checkbox.  This information will be useful later (to be covered in a different post).  Clicking "Next" the SQL is generated and present in the wizard.

This can be copied & pasted directly from here or pressing "Finish" will save the SQL to the file indicated at the top of the dialog box.  This file is added to the project.  The following prompt will appear when "Finish" is pressed.

This doesn't really matter as this is a throw away project but having the updated schemas maybe useful so go with "Yes".

The SQL can now be used to configure an empty SQL CE 4.0 database.  The easiest way is to open the SQL file and right-click selecting the "Execute SQL" menu item.

This brings up the SQL Server dialog from which if "New Database" is selected an CE 4 one can be specified.

Having specified a location and pressed "Ok" the SQL script is executed.  As can be seen below this is not without errors.  However, this isn't anything to worry about as the errors are to do with dropping tables and indices that currently don't exist as it's a newly created dB.  Performing the same steps but missing out the creation of the dB file as it already exists sees the SQL script execute flawlessly.

The final picture shows the newly created database in VS2010's Server Explorer demonstrating that the tables were indeed created.

The basis for this post is my experimentation on using NUnit to programmatically test some dB based functionality.  If a single instance of a database suffices for all your tests and you can execute the SQL by hand as above and then you can follow these steps.  In may case I want to a fresh database per test so I need to automate the running of the SQL Script combined the with the creation and destruction of the underlying database.  The creation and deletion aspect were covered in a previous post but the next step will have to wait until a later one.

Thursday, 3 May 2012

More computing humor

A few more computer/programming related jokes.  This time courtesy of the ACCU general mailing list:

  • I heard a good concurrency joke recently, about 10,000 threads. It was a bit contentious... (Ewan Milne)
  • A programmer walked into a Bar.  I say a Bar, it was actually a Foo. (Frances Buontempo)
  • Two programmers are sitting in a bar discussing static and dynamic languages. The next day they get a visit from the RSPCA. When they ask what it's concerning, the RSPCA man says "We got a tip off that you were using ducks for typing". (Anthony Williams)
  • An SEO expert walks into a bar, bars, pub, public house, Irish pub, drinks, beer…. (Anders Knatten) 

Monday, 16 April 2012

Unit Testing when the success case is compilation failure (with C++)

There is an issue with the use of Window’s COM types being used with STL containers in versions of Visual Studio prior to 2010. The crux of the matter is that various COM types define the address-of operator and instead of returning the real address of the object they return a logical address. If the STL container re-arranges its contents this can lead to corruption as it can unwittingly manipulate an object at the incorrect address.

The prescribed solution to this problem is to not place the COM types directly into the STL container but instead wrap them with the ATL CAdapt class.  When adopting this approach there are two important aspects to consider:

  • Firstly, is there a way to prevent incorrect usage of the containers?
  • Secondly, assuming this is possible, is there a way to make sure it covers the various permutations of STL containers and COM types that are being used?

It turns out that the first issue is easily solved using template specialization.  The hard part though is creating  a set of unit tests that ensure specializations have been created for all permutations and that they are active.  This is made even more difficult by the fact a successful use of the specialization results in compilation failure.

This too can be solved by combing various template mechanisms and techniques: SFINAE & Template Meta-programming etc.  In the April issue of the ACCU Overload journal I have written article that describes this problem along with the solution.  Please follow the link below (and then jump to page 24 in the PDF if it doesn't open there automatically).

The complete source code the article is also available on GitHut:

Monday, 2 April 2012

Using NUnit and Entity Framework DbContext to programmatically create SQL Server CE databases & specify the databse directory

NOTE: An update to the method used here is provided in this newer post: Integration Testing with NUnit and Entity Framework.

I won't go into the why but I wanted to write what probably amounts to an integration test of an Entity Framework model.  I decided to use NUnit for this.  Even though it's predominately for Unit Testing there's no reason why it can't be used for other forms of testing.  In fact I think the SpecFlow BDD framework eventually performs its tests using NUnit: It's not what you've got but what you do with it!

The application I'm writing uses SQL Express but for my tests I wanted to create & destroy a database frequently and locally so I opted to use SQL Server Compact Edition.  This is pretty easy to do with EF's DbContext: just create an instance of it, pass in either the name of the database or a Connection String, e.g.

public void TestWithConnectionString()
  var db = new DbContext("Name=Foo");


which references the following Connection String in the .config file

  <add name="Foo"
    connectionString="Data Source=foo.sdf"/>

As I'm going to be potentially creating many of these I wanted precise control over their name and location.  This meant I didn't really want to use a Connection String as this is more or less hard-coded in the .config file.

Instead I opted to create it programmatically.  By default DbContext expects to be using SQL Server in particular an instance of SQLExpress named .\SQLExpress.  This is easily changed by replacing the DefaultConnectionFactory with the factory class for SQL Server CE: SqlCeConnectionFactory.

The first parameter to the constructor is the type of the factory class which allows instances of different versions to be created. This is simply the providerName as per the Connection String.  The second parameter is the directory to create any new databases in.  The third parameter (unused in the example below) are options to append to the generated Connection String.  The code below will result in the creation of C:\UsersPete\TestDBs\bar.sdf assuming the directory exists and the user has appropriate permissions and bar.sdf does not already exist.

public void TestWithFactory()
  Database.DefaultConnectionFactory = 
    new SqlCeConnectionFactory(
      @"C:\Users\Pete\TestDBs\", "");

  var db = new DbContext("bar.sdf");


That's mainly it:  A simple way to programmatically create databases.  This code should really be moved to the SetUp method and a corresponding TearDown method added to delete the database; oh, and some tests!

I haven't got that far yet and the actual reason for writing the entry was for a short while despite specifying the directory for the databases, i.e. C:\Users\Pete\TestDBs they were being created in the current working directory.  This was because rather than just specifying the name of the database as the argument to DbContext I was passing the string "DataSource=bar.sdf" of which the name part appears to be an absolute path and thus override that specified in the SqlCeConnectionFactory.  As only a file name is present it uses the current working directory for the path element. If you've got the same issue (whether integration testing or not) this might save you a little time.

Wednesday, 18 January 2012

A C#/.NET Attributes Based Command Line Argument Parser

I've been meaning to add a blog entry for this for a while.  It's just a link to my latest Code Project article that went live last week.  It's a long piece describing a small library for handling the parsing of command line arguments in C# programs, either Console or GUI (there's a WPF example).

This is the first project I created using Test Driven Development so as well as the technical details of the library there's also a description of how I found TDD.

You can find it here:

Wednesday, 4 January 2012

Open Source C# Network File System (NFS) Server (for Windows)

Happy New Year!

Not a proper post but just a quick link to my latest Code Project article.  A few years ago I wrote an NFS Server (in C#).  I had reason to revisit this lately so I thought I might as well write it up as a Code Project article and Open Source it.  You can grab it from GitHub.