Constraint not being re-created after being dropped automatically (changed in 6.2)

If a table is created with a primary key default value of (newsequentialid()), and then in a subsequent migration that column is ALTERed, then the default will be removed and not recreated. This occurs in 6.2 and 6.3 but NOT in 6.1.

Model/Context Setup

    public class FooTable
    {
        public Guid Id { get; set; }
    }

    public class FooTableMap : EntityTypeConfiguration<FooTable>
    {
        public FooTableMap()
        {
           Property(t => t.Id).HasColumnName("FooId").HasDatabaseGeneratedOption(DatabaseGeneratedOption.Identity);
        }
    }

    public class FooContext : DbContext
    {
        public DbSet<FooTable> Foos { get; set; }

        public FooContext() : base("EFContext")
        {
        }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            modelBuilder.Configurations.AddFromAssembly(typeof(FooTableMap).Assembly);
        }
    }

Repro

Create an initial migration, you get something like this:

    public partial class InitialCreate : DbMigration
    {
        public override void Up()
        {
            CreateTable(
                "dbo.FooTables",
                c => new
                    {
                        FooId = c.Guid(nullable: false, identity: true),  // <<< Identity == true!
                    })
                .PrimaryKey(t => t.FooId);
            
        }
        
        public override void Down()
        {
            DropTable("dbo.FooTables");
        }
    }

Run this migration and you will get the table with the default value as expected.

Now add a new migration like this:

    public partial class NewMigration : DbMigration
    {
        public override void Up()
        {
            DropPrimaryKey("dbo.FooTables");
            AlterColumn("dbo.FooTables", "FooId", c => c.Guid(nullable: false, identity: true));  // <<< IDENTITY is *still* true
            AddPrimaryKey("dbo.FooTables", "FooId");
        }
        
        public override void Down()
        {
        }
    }

The migration defines the column exactly as it was in the original migration. Run the migration:

• On 6.1 the default value will still remain
• On 6.2 the default value will be removed

The SQL in 6.1 looks like:

ALTER TABLE [dbo].[FooTables] ALTER COLUMN [FooId] [uniqueidentifier] NOT NULL

in 6.2 (and 6.3) it is:

SELECT @var0 = name
FROM sys.default_constraints
WHERE parent_object_id = object_id(N'dbo.FooTables')
AND col_name(parent_object_id, parent_column_id) = 'FooId';
IF @var0 IS NOT NULL
    EXECUTE('ALTER TABLE [dbo].[FooTables] DROP CONSTRAINT [' + @var0 + ']')
ALTER TABLE [dbo].[FooTables] ALTER COLUMN [FooId] [uniqueidentifier] NOT NULL

The drop contraint removes the default value, and nothing adds it back in.

This issues was introduced by this commit https://github.com/aspnet/EntityFramework6/pull/137/commits/15de49003c43365307408b408dc57252847f9803

Possible Fix Add an additional WHERE clause to the contraint sql to exclude default values? (AND type <> 'D' at the end)

Further technical details

EF version: 6.2 Database Provider: MSSQL Operating system: Windows 10 IDE: Visual Studio 2019 / Rider 2019.2 [EfMigrationTest.zip]

Complete repro solution (using EF6.2 - downgrade to 6.1 and re-run migrations to see the old SQL)

(https://github.com/aspnet/EntityFramework6/files/3609403/EfMigrationTest.zip)

[slovely]

Thank you. By the way - we upgraded a fairly large app from EF6.1 to EF6.3, moved from 4.6.1 to dotnetcore v3, and it was really easy. Also CPU usage appears to be nearly 50% less, with no effort spent on optimisations. Just a little “thank you” to offset the bug 😃

[slovely]

@ajcvickers - Fair enough 😃 I would guess it is pretty low-impact, especially as it already existed in 6.2. It’s possible some more people might upgrade from <6.1 to 6.3 for the .net core support though.

Just in case someone stumbles on this issue the workaround we did was to modify the migrations from:

AlterColumn("dbo.FooTables", "FooId", c => c.Guid(nullable: false, identity: true)); 

to:

AlterColumn("dbo.FooTables", "FooId", c => c.Guid(nullable: false, defaultValueSql: "newsequentialid()")); 

Please feel free to close, or if you think it’s worthwhile for me to create a PR with a possible fix (not looked at the migration code before so can’t promise I will manage it!)