Code-based Configuration:

Entity Framework 6 has introduced code based configuration. Now, you can configure Entity Framework related settings using the code which had been previously configured in the <entityframework> section of the app.config. However, app.config takes precedence over code-based configuration. In other words, if a configuration option is set in both the code and in the app.config, then the setting in the app.config is used.

Let's see how to implement code-based configuration using Entity Framework 6.

First of all, you need to create a new class that derives the DbConfiguration (System.Data.Entity.DbConfiguration) class :

public class FE6CodeConfig : DbConfiguration
{
    public FE6CodeConfig()
    {
        //define configuration here
    }
}

Now, you can set codeConfigurationType in the app.config as shown below:

<entityFramework codeConfigurationType="EF6DBFirstTutorials.FE6CodeConfig, EF6DBFirstTutorials">
</entityFramework>

Or you can use the DbConfigurationType attribute on the context class to set the code-based configuration class:

async query output

Note: EF does not support having multiple configuration classes used in the same AppDomain. If you use this attribute, to set different configuration classes for two contexts, then an exception will be thrown.

Now, you can use different methods of DbConfiguration using this in the constructor as shown below:

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Let's see how to do different settings using code-based configuration as well as the app.config.

Set Default Connection Factory:

Code-based configuration:

public class FE6CodeConfig : DbConfiguration
{
    public FE6CodeConfig()
    {
        this.SetDefaultConnectionFactory(new System.Data.Entity.Infrastructure.SqlConnectionFactory());
    }
}

app.config:

<entityFramework>
    <defaultConnectionFactory type="System.Data.Entity.Infrastructure.SqlConnectionFactory, EntityFramework" />
</entityFramework>

Set Database Provider:

Code-based configuration:

public class FE6CodeConfig : DbConfiguration
{
    public FE6CodeConfig()
    {
        this.SetProviderServices("System.Data.SqlClient", 
                System.Data.Entity.SqlServer.SqlProviderServices.Instance);
    }
}

app.config:

<entityFramework>
    <providers>
        <provider invariantName="System.Data.SqlClient" type="System.Data.Entity.SqlServer.SqlProviderServices, EntityFramework.SqlServer" />
    </providers>
</entityFramework>

Set Database Initializers:

You can set database initializers (for Code-First only) using code-based configuration as shown below:

public class FE6CodeConfig : DbConfiguration
{
    public FE6CodeConfig()
    {
        this.SetDatabaseInitializer<SchoolDBEntities>(new CustomDBInitializer<SchoolDBEntities>());
    }
}

app.config:

<entityFramework>
    <contexts>
        <context type="EF6DBFirstTutorials.SchoolDBEntities, EF6DBFirstTutorials"  >
            <databaseInitializer   type="EF6DBFirstTutorials.CustomDBInitializer , EF6DBFirstTutorials">
            </databaseInitializer>
        </context>
    </contexts>    
</entityFramework>