EF Code first set a foreign key with an empty lookup table

Question

I have a problem with EF code first migration related to a lookup table and foreign keys. Let's say I have this two classes in my code:

public class Test
{
    [Key]
    public long Id { get; set; }

    [Required]
    public string Title { get; set; }

    [Required, DisplayName("Test type")]
    public TestType TestType { get; set; }
}

public class TestType
{
    public int Id { get; set; }
    public string Name { get; set; }
}

TestType is a typical lookup table and I usually fill them up in the Seed() method:

context.TestTypes.AddOrUpdate(
    it => it.Name,
    new TestType() { Name = "Drug" },
    new TestType() { Name = "Educational" },
    new TestType() { Name = "Other" }
);

When I create the table with the relationship I get the following migration:

CreateTable(
    "dbo.TestTypes",
    c => new
        {
            Id = c.Int(nullable: false, identity: true),
            Name = c.String(),
        })
    .PrimaryKey(t => t.Id);

AddColumn("dbo.Tests", "TestType_Id", c => c.Int(nullable: false));
CreateIndex("dbo.Tests", "TestType_Id");
AddForeignKey("dbo.Tests", "TestType_Id", "dbo.TestTypes", "Id", cascadeDelete: true);

Now, if I perform the migration of course I will get an error since the foreign key cannot be respected given the fact that the lookup table is still empty and the column created does not have a default value.

In DEVELOPMENT I am able to solve this by simply creating two migrations, the first one to create the lookup table and the second one to set the foreign key. If I run them separately then the Seed method after the first one will fill the table and I can tweak the column creation to pick up the values from the DB to prefill the column before creating the foreign key, a bit like this:

AddColumn("dbo.Tests", "TestType_Id", c => c.Int(nullable: false));
Sql("UPDATE dbo.Tests SET TestType_Id = (SELECT TOP 1 Id FROM dbo.TestTypes)");
CreateIndex("dbo.Tests", "TestType_Id");
AddForeignKey("dbo.Tests", "TestType_Id", "dbo.TestTypes", "Id", cascadeDelete: true);

Then when I run it everything works.

Now, in PRODUCTION I don't have the same luxury, since ALL the migrations are run before the Seed method is run, I will always have the same problem.

I know I could potentially run the migrations in stepped order on the production DB as well but that does not really solve the problem... Let's say a colleague of mine updates his working copy and runs the migrations, all will be run in order and he will encounter the error for sure.

Answer 1

I'm not sure on the current state of your database but I would define your models like this

public class Test
{
    [Key]
    public long Id { get; set; }

    [Required]
    public string Title { get; set; }

    [Required]
    [ForeignKey("TestType")]
    public int TestTypeId { get; set; }

    [DisplayName("Test type")]
    public virtual TestType TestType { get; set; }
}

public class TestType
{
    [Key]
    public int Id { get; set; }

    public string Name { get; set; }
}

Which results in the following migration when the tables don't exist already. I always find describing the foreign keys explicitly works better.

public override void Up()
{
    CreateTable(
        "dbo.Tests",
        c => new
            {
                Id = c.Long(nullable: false, identity: true),
                Title = c.String(nullable: false),
                TestTypeId = c.Int(nullable: false),
            })
        .PrimaryKey(t => t.Id)
        .ForeignKey("dbo.TestTypes", t => t.TestTypeId)
        .Index(t => t.TestTypeId);

    CreateTable(
        "dbo.TestTypes",
        c => new
            {
                Id = c.Int(nullable: false, identity: true),
                Name = c.String(),
            })
        .PrimaryKey(t => t.Id);
}

The seed should then work fine as long as the Test table is empty?