MigrateDatabaseToLatestVersion and dbo.__MigrationHistory - entity-framework

Question

I am trying to deploy an MVC4 application that is built using EF5 codefist and migrations.
I want the app to update the database when I in the future deploy new versions of the app with new migrations, so in Global.asax I do this:
Database.SetInitializer(new MigrateDatabaseToLatestVersion<GoDealMvc4Context, Configuration>());
using (var ctx = new GoDealMvc4Context()) {
ctx.Database.Initialize(false);
}
The initial database on the server is deployed by attaching an MDF file copied from my dev machine. This database contains the __MigrationsHistory system table. So this database should not need to execute any migrations, because it is up to date with latest migration.
When I try to start the app on the server, it I get this error:
There is already an object named 'UserProfile' in the database.
[SqlException (0x80131904): There is already an object named 'UserProfile' in the database.]
System.Data.SqlClient.SqlConnection.OnError(SqlException exception, Boolean breakConnection, Action`1 wrapCloseInAction) +388
System.Data.SqlClient.TdsParser.ThrowExceptionAndWarning(TdsParserStateObject stateObj, Boolean callerHasConnectionLock, Boolean asyncClose) +688
System.Data.SqlClient.TdsParser.TryRun(RunBehavior runBehavior, SqlCommand cmdHandler, SqlDataReader dataStream, BulkCopySimpleResultSet bulkCopyHandler, TdsParserStateObject stateObj, Boolean& dataReady) +4403
System.Data.SqlClient.SqlCommand.RunExecuteNonQueryTds(String methodName, Boolean async, Int32 timeout) +2755286
System.Data.SqlClient.SqlCommand.InternalExecuteNonQuery(TaskCompletionSource`1 completion, String methodName, Boolean sendToPipe, Int32 timeout, Boolean asyncWrite) +527
System.Data.SqlClient.SqlCommand.ExecuteNonQuery() +290
System.Data.Entity.Migrations.DbMigrator.ExecuteSql(DbTransaction transaction, MigrationStatement migrationStatement) +247
System.Data.Entity.Migrations.DbMigrator.ExecuteStatements(IEnumerable`1 migrationStatements) +202
System.Data.Entity.Migrations.DbMigrator.ApplyMigration(DbMigration migration, DbMigration lastMigration) +472
System.Data.Entity.Migrations.DbMigrator.Upgrade(IEnumerable`1 pendingMigrations, String targetMigrationId, String lastMigrationId) +175
System.Data.Entity.MigrateDatabaseToLatestVersion`2.InitializeDatabase(TContext context) +150
System.Data.Entity.Internal.InternalContext.PerformInitializationAction(Action action) +66
System.Data.Entity.Internal.InternalContext.PerformDatabaseInitialization() +225
System.Data.Entity.Internal.RetryAction`1.PerformAction(TInput input) +208
System.Data.Entity.Internal.LazyInternalContext.InitializeDatabaseAction(Action`1 action) +235
GoDeal.Mvc4.MvcApplication.Application_Start() +342
So apparently the app thinks it needs to apply a migration even though the __MigrationHistory table is present in the database with this content:
MigrationId Model ProductVersion
201210161046508_initial 0x1F8... 5.0.0.net45
and the app contains a single migration class:
201210161046508_initial.cs:
public partial class initial : DbMigration
{
public override void Up()
{
CreateTable(
"dbo.UserProfile",
....
So my questions are:
1) why do my application think it needs to apply this migration when the contents of the __MigrationsHistory table is as described.
2) is this the recommended way of making an application that automatically applies new migrations wehn restarted on a new version.

Answer 1

There is also another NASTY gotcha here for anyone looking for answers. Check the content of the
[dbo].[__MigrationHistory] table column ContextKey
This table Tells how the DB was created (migration mode, Create mode etc...) was created. AND with what Migration Configuration Program. I got hurt with a change of MigrationsConfiguration Class name.
Changing the entry in table worked :-) Or renaming your code back.

Answer 2

1)
As your migration is called "initial" rather than "InitialCreate" this implies that you created this manually and when you enabled code first migrations the database didn't exist already. Or at least the context was not pointing to it. http://msdn.microsoft.com/en-us/data/jj591621.aspx
I believe that MigrateDatabaseToLatestVersion will first trying the create the entity tables for entities that existed before migrations was enabled. As the InitialCreate migration does not exist in your database this first step will then clash with the tables that already exist. Sorry this is a bit vague but I don't fully understand it. To fix this I would remove the migrations by deleting them (first saving any custom changes) and then enable them again with the context pointing at the exiting DB. You should now have an "InitialCreate" migration. You should now be able to copy up the db and use MigrateDatabaseToLatestVersion in the production environment.
2)
Personally letting code first update a production DB worries me quite a bit. I have been using update-database -script -sourcemigration xx to generate the scripts to migrate the DB. This way you can see what is going to happen before you break anything. It also allows you to run in a transaction and roll back after a failure.

Answer 3

In my case this issue was caused by missing migration. I did some changes into model, but I forgot to create new migration file.
My solution is to run in Package Manager Console: Add-Migration MyMigrationName

Answer 4

Just in case someone else encounters SqlException with the message There is already an object named '<TABLE_NAME>' in the database. after changing the model while using automatic migrations. It seems the migrations' Configuration requires in some cases explicit naming of the context key:
internal sealed class Configuration : DbMigrationsConfiguration<MyDatabaseContext>
{
public Configuration ()
{
AutomaticMigrationsEnabled = true;
ContextKey = "MyNamespace.MyDatabaseContext"; // this line was missed
}
protected override void Seed(MyDatabaseContext context)
{
}
}
After adding the line above to the constructor of Configuration, the migration ran without any issues. You can check which ContextKey value is already in use in the __MigrationHistory database.