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

entity-framework entity-framework-migrations
Dan Cook picture Dan Cook · Jul 19, 2015 · Viewed 19.2k times · Source

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" });
            DropTable("dbo.Bingo_Bonus");
            DropTable("dbo.Bingo");
            DropTable("dbo.Bingo_Review");
            DropTable("dbo.Bingo_Review_Text");
            DropTable("dbo.Bingo_Bonus_Amount");
            DropTable("dbo.Bingo_Bonus_Type");
        }

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?

Answer

Andy Raddatz picture Andy Raddatz · Dec 31, 2015

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]");

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