Question

Now i’m using EF6 Alpha, and when using migration, it will add a new migration log into the __MigrationHistory table.

In EF6, The __MigrationHistory table has a new column called “ContextKey”. After testing, I found there are two default “ContextKey” value:

1. The full name of DbContext’s derived class.This happens when i run the code:

   Database.CreateIfNotExists();
   

2. The full name of DbMigrationsConfiguration’s derived class. This happens when i run the code:

   public ArticleDbContext()
   {   
       Database.SetInitializer(new MigrateDatabaseToLatestVersion<ArticleDbContext, ArticleConfiguration>());
   }
   

The first time i run the application, “Database.CreateIfNotExists();” create a new database for me, also all tables that map to the models defined in ArticleDbContext, and then add a __MigrationHistory row which ContextKey’s value is “Module.Article.Model.ArticleDbContext”.

And then “Database.SetInitializer(new MigrateDatabaseToLatestVersion());” will be runned, this code will generate a new ContextKey “PowerEasy.Module.Article.Migrations.ArticleConfiguration”. Migration query the __MigrationHistory table with this ContextKey and find out there’s no data. So again it will create all tables that map to the models defined in ArticleDbContext, but the tables are already exist in the database, so an exception will be throwed, and tell me “the table XXX is already existed”.

How can i solve this?

Answer 1

You should not mix Migrations and the Database.CreateIfNotExists method (or any of the initializers built on top of it). Migrations will take care of creating the database if it does not already exist.

As an alternative to the Migrations initializer, you can also apply migrations using the DbMigrator.Update method. This is useful if you want to create/update the database before it would otherwise be triggered by the initializer.