If you want to switch between in-memory stub data and a database during runtime with Entity Framework 5.0, you have several options, some of them are:
– Using a second level cache mechanism like http://www.codeproject.com/Articles/435142/Entity-Framework-Second-Level-Caching-with-DbConte , filling the cache before use and setting the expiration time to infinite.
– Creating a extension method on the DbSet class that uses only the DbSet (for direct database access) or DbSet.Local for in-memory stub data, based on some parameter.
– Implement a MemoryPersistenceDbContext and MemoryPersistenceDbSet.
This post will focus on the last option.
Create a new MVC4 project in Microsoft Visual Studio 2010
File > New > Project
Add Entity Framework 5.0 NuGet package
Rightclick solution > Manage NuGet Packages for Solution…
I added 2 tables to a Research database on a LocalDb SQL Server 2012 instance
Add *.edmx model
Right click on the models folder:
ModelName = ResearchModel.edmx
DbContext name = ResearchUow
(UOW = Unit of work)
Model namespace = ResearchModel
Check all tables
Add code generation item
Open the ResearchUow.edmx > right click > Add Code Generation Item…
Code generation item name = ResearchModel.tt
Now the project looks like
Add an IEntity interface
This interface will be used to make the Find function work.
Add a MemoryPersistenceDbSet.cs in the Models folder
This will be used to store the data in-memory instead of in the database.
Change the ResearchModel.tt file, so all generated POCO entities derive from IEntity
Open the ResearchModel.tt files and change the line
<#=codeStringGenerator.EntityClassOpening(entity)#>
to
<#=codeStringGenerator.EntityClassOpening(entity)#> : IEntity
and click save, on save of the ResearchModel.tt file, the POCO entities will be regenerated and will now all implement the IEntity interface:
Change the ResearchModel.Context.tt file, so the IResearchUow interface, the ResearchUow class and the MemoryPersistenceResearchUow will be created.
Open the ResearchModel.Context.tt file and find the code:
<#=Accessibility.ForType(container)#> partial class <#=code.Escape(container)#> : DbContext
{
public <#=code.Escape(container)#>()
: base("name=<#=container.Name#>")
{
<#
if (!loader.IsLazyLoadingEnabled(container))
{
#>
this.Configuration.LazyLoadingEnabled = false;
<#
}
#>
}
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
throw new UnintentionalCodeFirstException();
}
<#
foreach (var entitySet in container.BaseEntitySets.OfType<EntitySet>())
{
#>
<#=codeStringGenerator.DbSet(entitySet)#>
<#
}
foreach (var edmFunction in container.FunctionImports)
{
WriteFunctionImport(typeMapper, codeStringGenerator, edmFunction, modelNamespace, includeMergeOption: false);
}
#>
}
<#
if (!String.IsNullOrEmpty(codeNamespace))
{
PopIndent();
#>
}
<#
}
#>
Replace by
<#=Accessibility.ForType(container)#> partial interface IResearchlUow
{
<#
foreach (var entitySet in container.BaseEntitySets.OfType<EntitySet>())
{
#>
<#=codeStringGenerator.IDbSet(entitySet)#>
<#
}
foreach (var edmFunction in container.FunctionImports)
{
WriteFunctionImport(typeMapper, codeStringGenerator, edmFunction, modelNamespace, includeMergeOption: false);
}
#>
int SaveChanges();
}
<#=Accessibility.ForType(container)#> partial class <#=code.Escape(container)#> : DbContext, IResearchUow
{
<#
foreach (var entitySet in container.BaseEntitySets.OfType<EntitySet>())
{
#>
<#=codeStringGenerator.DbSet(entitySet)#>
<#
}
foreach (var edmFunction in container.FunctionImports)
{
WriteFunctionImport(typeMapper, codeStringGenerator, edmFunction, modelNamespace, includeMergeOption: false);
}
#>
public <#=code.Escape(container)#>() : base("name=<#=container.Name#>")
{
<#
if (!loader.IsLazyLoadingEnabled(container))
{
#>
this.Configuration.LazyLoadingEnabled = false;
<#
}
#>
}
public <#=code.Escape(container)#>(string connection) : base(connection)
{
<#
if (!loader.IsLazyLoadingEnabled(container))
{
#>
this.Configuration.LazyLoadingEnabled = false;
<#
}
#>
}
protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
throw new UnintentionalCodeFirstException();
}
}
<#=Accessibility.ForType(container)#> partial class MemoryPersistenceResearchUow : <#=code.Escape(container)#>
{
public MemoryPersistenceResearchUow()
{
Seed();
}
public void ClearAll()
{
<#
foreach (var entitySet in container.BaseEntitySets.OfType<EntitySet>())
{
#>
<#=codeStringGenerator.DbSetInConstructor(entitySet)#>
<#
}
#>
}
public override int SaveChanges()
{
return 0;
}
}
<#
if (!String.IsNullOrEmpty(codeNamespace))
{
PopIndent();
#>
}
<#
}
#>
and find
public string DbSet(EntitySet entitySet)
{
return string.Format(
CultureInfo.InvariantCulture,
"{0} DbSet<{1}> {2} {{ get; set; }}",
Accessibility.ForReadOnlyProperty(entitySet),
_typeMapper.GetTypeName(entitySet.ElementType),
_code.Escape(entitySet));
}
Replace by
public string IDbSet(EntitySet entitySet)
{
return string.Format(
CultureInfo.InvariantCulture,
"IDbSet<{0}> {1} {{ get; set; }}",
_typeMapper.GetTypeName(entitySet.ElementType),
_code.Escape(entitySet));
}
public string DbSet(EntitySet entitySet)
{
return string.Format(
CultureInfo.InvariantCulture,
"{0} IDbSet<{1}> {2} {{ get; set; }}",
Accessibility.ForReadOnlyProperty(entitySet),
_typeMapper.GetTypeName(entitySet.ElementType),
_code.Escape(entitySet));
}
public string DbSetInConstructor(EntitySet entitySet)
{
return string.Format(
CultureInfo.InvariantCulture,
"this.{0} = new MemoryPersistenceDbSet<{0}>();",
_typeMapper.GetTypeName(entitySet.ElementType));
}
Now on save of the ResearchModel.Context.tt T4 template will generate the following code:
Add a partial class file for the MemoryPersistenceResearchUow
Every time you update the ReserachModel.edmx from the database or save the T4 templates ResearchModel.tt and ResearchModel.Context.tt, the T4 templates will execute and regenerate all POCO entities and the IResearchUow interface, ResearchUow class and the MemoryPersistenceResearchUow. To prevent the code that seeds the in-memory UOW to be overwritten a partial class MemoryPersistenceResearchUow is created.
Add a IResearchUowFactory and ResearchUowFactory that will contain the logic to create a ResearchUow or an MemoryPersistenceResearchUow.
The project will no look like:
Add appSetting "UseStubs" to the Web.config
Install an IoC container by using NuGet, in this case I will use ninject:
Install Ninject and Ninject.MVC3 (no MVC4 available yet, but works just fine) this will also install Ninject.Web.Common.
In the App_Start folder change the NinjectWebCommon.cs
Fill the RegisterService function:
In the Controllers folder change the HomeControler, add:
Result
This results in:
The text "First person name [Roel van Lisdonk]" is shown. This was the data from the seed method:
this.Person.Add(new Person { Id = 1, Name = "Roel van Lisdonk" });
and not from the real database, because the database at this point is empty.
This proves we can switch using in-memory stub data or the real database by changing a appSetting in the web.config.
Don’t forget to fix the unit tests.
In the unit tests for the HomeController, change the lines:
to
Now you are able to use the ResearchUow within your HomeController and switch between the MemoryPersistenceResearchUow and the ResearchUow by changing the appSetting UseStubs.
