Entity framework 5 Migrations, Multiple migrations.

When you run the Update-Database command (Update-Database -ConfigurationTypeName MyDbConfig) migrate.exe checks which migrations still need to be executed on the target database by comparing the migration scripts present to the subscriptions in the dbo._MigrationHistory table of the target database. By default all migrations are then applied. 

Take note that each of those migrations runs in it's own transaction. This could get you into trouble when you deploy a single release of your application with multiple migration files. If the last migration should fail, all previous migrations changes are kept, leaving your model and database unsynchronised. You can avoid this by removing all migrations and their corresponding entries in the dbo._MigrationHistory table and creating a big single migration for your application's release.

If you did get into trouble you can always rollback your application and revert to the corresponding migration. When reverting, the "Down" method implementation of the migration is used. This means that if you edited the "Up" as explained in Seed & Sql and forgot to implement the rollback in "Down" you might still be in trouble.

PM> Update-Database -ConfigurationTypeName MyDbConfig -targetMigration "Version2"

Specify the '-Verbose' flag to view the SQL statements being applied to the target database.

Reverting migrations: [000000000000000_Version3].

Reverting code-based migration: 000000000000000_Version3.

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