Entity Framework Migrations can't drop table because of foreign key constraint

ef-migrations entity-framework


I have reverse-engineered the existing database to the code-first model. Some tables are to be kept but most are to be removed and completely re-architected for the new version.

I delete some old classes and their mapping and add-migration.

The migration looks like this:

  public override void Up()
            DropForeignKey("dbo.Bingo_Review", "BingoID", "dbo.Bingo");
            DropForeignKey("dbo.Bingo_Review_Text", "BingoReviewID", "dbo.Bingo_Review");
            DropForeignKey("dbo.Bingo_Bonus", "BingoID", "dbo.Bingo");
            DropForeignKey("dbo.Bingo_Bonus_Amount", "BingoBonusID", "dbo.Bingo_Bonus");
            DropIndex("dbo.Bingo_Bonus", new[] { "BingoID" });
            DropIndex("dbo.Bingo_Review", new[] { "BingoID" });
            DropIndex("dbo.Bingo_Review_Text", new[] { "BingoReviewID" });
            DropIndex("dbo.Bingo_Bonus_Amount", new[] { "BingoBonusID" });

However when I run the migration, I get the following error in package manager console.

Could not drop object 'dbo.Bingo_Bonus' because it is referenced by a FOREIGN KEY constraint.

Why do I get this error when the migration should have already dropped any foreign keys prior to the drop table command? Is there any way around this?

7/19/2015 11:38:06 AM

Popular Answer

If the dbo.Bingo_Bonus table name has ever changed, or if any of the columns in the foreign key relationships have changed, EF does not rename the foreign key constraints automatically to match. I had a similar problem and I had to manually add a line like this because the DropForeignKey() function was not actually deleting the key it was supposed to:

Sql(@"ALTER TABLE [dbo].[MyTable] DROP CONSTRAINT [FK_dbo.Constraint_Name_From_Before_Table_Change]");
12/31/2015 5:31:56 PM

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