对现有数据库使用实体框架。 防止表删除？

Question

I'm updating an old website's forums to the open source MVCForum . MVCForum uses Code First Entity Framework which from what I can tell makes it a tricky to integrate with an existing database(at least for a beginner like me :/). I've worked with entity framework briefly from scratch, but never in an already designed application with models completed.

Is there a way to integrate a Code First EF project's required tables into a database without removing all tables that aren't directly associated with said project? Having all the website's tables in one database and not just the forums' tables would be ideal.

Also, is there any way to force an update to a database through Entity Framework? Just a brute force "Check if these tables exist, if not create them." I've run into the issue of the EF thinking my database has the necessary tables(I think that's the problem...) and it doesn't.

Apologies if this doesn't make sense. I may not even understand EF enough to properly ask questions about it.

Thanks

Answer 1

Yes, if your DbSet names in Model will be unique (vs. DB table names), EF just create __MigrationHistory table and add new tables corresponding to your EF model. This is default behavior with CreateDatabaseIfNotExists initializer.

In your case you should not use :

• DropCreateDatabaseWhenModelChanges
• DropCreateDatabaseAlways

because this initialisers will drop the database.

Reverse engineering

Optionally you can just create your new tables in DB and then use EF code first common way. In this case EF will not change your DB. Notice that in this case you must make all changes in your DB manually.

Answer 2

That project looks prepped for migrations so all you should need to do is point your connection string where you want. On first run it will create the database so now you want to create a baseline migration that takes a snapshot of the existing schema:

1) add-migration Initial -IgnoreChanges  // tells EF tables exist
2) update-database  // Adds record to __MigrationHistory table

Now you can make your own changes and follow the normal code first workflow:

1) Change schema
2) add-migration foo
3) update-database