Entity Framework 6

SQL CE and namespaces

We use SQL CE in our unit test project to test our EF6 queries. This works pretty well and Code first setup makes sure each test gets a fresh CE database to work with.

We ran into a problem where two EF types had the same table name but inside different schemas. CE does not support schemas and this resulted in naming conflicts when setting up database. My solution was to create a little convention.

public class BakeSchemaIntoTableNameConvention : IStoreModelConvention<EntityType>
{
    public void Apply(EntityType item, DbModel model)
    {
        var entitySet = model.StoreModel.Container.EntitySets.Single(es => es.ElementType == item);
        entitySet.Table = $"{entitySet.Schema}_{entitySet.Table}";
    }
}

It bakes the schema into the table name like dbo_MyTable. You add the convention like.

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    modelBuilder.Conventions.Add<BakeSchemaIntoTableNameConvention>();

    modelBuilder.Configurations.AddFromAssembly(typeof (MyContext).Assembly);
}

You do not want to add this for production code so what I did was create a public event on the context. And call it from the OnModelCreating method.

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    ModelCreating?.Invoke(this, modelBuilder);

    modelBuilder.Configurations.AddFromAssembly(typeof (MyContext).Assembly);
}

Call it from your Unittest project like.

ctx.ModelCreating += (s, e) => e.Conventions.Add<BakeSchemaIntoTableNameConvention>();
Advertisements

Parallel executed Tasks with isolated scopes

My current customers infrastructure is heavily dependent on external suppliers of data. Because of the nature of the data the system often have to-do the requests in real time while the end-customer is waiting for the response. Parallel tasks comes in handy when you want to aggregate data from several end points, both because it puts less strain on the Thread Pool and that your response time will be faster because you do not need to wait for each to complete (Parallel vs Sequential).

The problem starts with frameworks that does not play nice with sharing their resources over multiple Tasks/Threads, an example of this is the Entity Framework DbContext. One way is to marshall the lifetime of the context yourself and spawn one for each parallel task. But this is not a solid design, if you use a IOC you want any object in the current graph to receive the same instance of the DbContext without bothering with lifetime code. I created a little class called TaskRunner for this purpose (more…)

Entity framework 6 and fluent mapping

If you google for EF and fluent mapping this is the first hit you get which is not strange since its the official MSDN page about fluent mapping in EF6.

They only discuss overriding the OnModelCreating method and configure the mapping inline in that method. And this is the most common way of dealing with fluent mapping out there in the community. But there is a much better and seperated way of doing it which MSDN fail to show.

System.Data.Entity.ModelConfiguration.EntityTypeConfiguration

This little class is your salvation when working with Fluent mapping in large enterprise systems. Implement it like. (more…)