Previous
Next

Database Initialization Strategies in EF 6 Code-First

You already created a database after running your Code-First application the first time, but what about the second time onwards? Will it create a new database every time you run the application? What about the production environment? How do you alter the database when you change your domain model? To handle these scenarios, you have to use one of the database initialization strategies.

There are four different database initialization strategies:

  1. CreateDatabaseIfNotExists: This is the default initializer. As the name suggests, it will create the database if none exists as per the configuration. However, if you change the model class and then run the application with this initializer, then it will throw an exception.
  2. DropCreateDatabaseIfModelChanges: This initializer drops an existing database and creates a new database, if your model classes (entity classes) have been changed. So, you don't have to worry about maintaining your database schema, when your model classes change.
  3. DropCreateDatabaseAlways: As the name suggests, this initializer drops an existing database every time you run the application, irrespective of whether your model classes have changed or not. This will be useful when you want a fresh database every time you run the application, for example when you are developing the application.
  4. Custom DB Initializer: You can also create your own custom initializer, if the above do not satisfy your requirements or you want to do some other process that initializes the database using the above initializer.

To use one of the above DB initialization strategies, you have to set the DB Initializer using the Database class in a context class, as shown below:

public class SchoolDBContext: DbContext 
{
    public SchoolDBContext(): base("SchoolDBConnectionString") 
    {
        Database.SetInitializer<SchoolDBContext>(new CreateDatabaseIfNotExists<SchoolDBContext>());

        //Database.SetInitializer<SchoolDBContext>(new DropCreateDatabaseIfModelChanges<SchoolDBContext>());
        //Database.SetInitializer<SchoolDBContext>(new DropCreateDatabaseAlways<SchoolDBContext>());
        //Database.SetInitializer<SchoolDBContext>(new SchoolDBInitializer());
    }

    public DbSet<Student> Students { get; set; }
    public DbSet<Standard> Standards { get; set; }
}

You can also create your custom DB initializer, by inheriting one of the initializers, as shown below: 

public class SchoolDBInitializer :  CreateDatabaseIfNotExists<SchoolDBContext>
{
    protected override void Seed(SchoolDBContext context)
    {
        base.Seed(context);
    }
}

In the above example, the SchoolDBInitializer is a custom initializer class that is derived from CreateDatabaseIfNotExists. This separates the database initialization code from a context class.

Set the DB Initializer in the Configuration File

You can also set the db initializer in the configuration file. For example, to set the default initializer in app.config:

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <appSettings>
    <add key="DatabaseInitializerForType SchoolDataLayer.SchoolDBContext, SchoolDataLayer"         
        value="System.Data.Entity.DropCreateDatabaseAlways`1[[SchoolDataLayer.SchoolDBContext, SchoolDataLayer]], EntityFramework" />
    </appSettings>
</configuration>

You can set the custom DB initializer, as follows: 

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <appSettings>    
    <add key="DatabaseInitializerForType SchoolDataLayer.SchoolDBContext, SchoolDataLayer"
            value="SchoolDataLayer.SchoolDBInitializer, SchoolDataLayer" />
    </appSettings>
</configuration>

Turn off the DB Initializer

You can turn off the database initializer for your application. Suppose that you don't want to lose existing data in the production environment, then you can turn off the initializer, as shown below: 

public class SchoolDBContext: DbContext 
{
    public SchoolDBContext() : base("SchoolDBConnectionString")
    {            
        //Disable initializer
        Database.SetInitializer<SchoolDBContext>(null);
    }
    public DbSet<Student> Students { get; set; }
    public DbSet<Standard> Standards { get; set; }
}

You can also turn off the initializer in the configuration file, for example: 

<?xml version="1.0" encoding="utf-8" ?>
<configuration>
    <appSettings>    
    <add key="DatabaseInitializerForType SchoolDataLayer.SchoolDBContext, SchoolDataLayer"
            value="Disabled" />
    </appSettings>
</configuration>
Previous
Next