Question

I have a scenario where i would like to change the primary key name in an entity and be able to run update-database -force. See below for code and error getting when i try.

Entity was:

public class Team
{
    [Key]
    [HiddenInput(DisplayValue = false)]
    public virtual int Id { get; set; }

    [Display(Name = "Full Name:")]
    public virtual string Name { get; set; }
}

Entity Changed to:

public class Team
{
    [Key]
    [HiddenInput(DisplayValue = false)]
    public virtual int TeamId { get; set; }

    [Display(Name = "Full Name:")]
    public virtual string Name { get; set; }
}

When i run Update-database -Force i get the following error.

Multiple identity columns specified for table 'Teams'. Only one identity column per table is allowed.

Its a matter of naming convention and i need this to be TeamId when i reference it latter, simply Id conflicts with child entity classes.

Any ideas on how i can do this successfully?

Answer 1

Depends on the version of EF you are using.
Even with migrations the result that you will see is something like:

“drop column Id ” and “add column TeamId”.

With this you will lose all values and “child connections”……

The only “secure” solution I am seeing at this point is a mix of Migrations and “hand SQL operations”.

EASY solution:

1- taking in consideration that you already have a “base” migration creating the table with ID, now create the new migration with the “update”. Now do NOT run it yet.

2- Open that file and write a new line BEFORE the generated lines and use a SQL command, something like this:

     SQL("ALTER TABLE table_name RENAME COLUMN old_name to new_name;");

This will change the name BEFORE the migration deletes the column and create a new one, what will happen is: you change the name before the delete, then the delete is executed but it will “fail” but it will not hurt nothing.

But now you ask: why do I do this? well if you are using migrations even if you delete the lines to delete the column and create a new one, the next time you create automatically a new migration file this new lines will be there…… this is why.

UPDATED ANSWERS #1

When I talk about Entity Framework Migrations I am referring to this:
http://blogs.msdn.com/b/adonet/archive/2012/02/09/ef-4-3-code-based-migrations-walkthrough.aspx
When you Run the ‘Add-Migration AddBlogUrl’ command in Package Manager Console, a new file (*.cs) is created.

Example of this file migration file with SQL commands:

public partial class AddAbsencesTypesAndCategories : DbMigration
    {
        public override void Up()
        {
            CreateTable(
                "pvw_AbsenceType",
                c => new
                    {
                        Id = c.Int(nullable: false, identity: true),
                        Name = c.String(nullable: false),
                        CountAsVacation = c.Boolean(nullable: false),
                        IsIncremental = c.Boolean(nullable: false),
                    })
                .PrimaryKey(t => t.Id);

          .....

            AddColumn("pvw_Absence", "CategoryId", c => c.Int(nullable: false));
                        AddForeignKey("pvw_Absence", "StatusId", "pvw_AbsenceStatusType", "Id");
            AddForeignKey("pvw_Absence", "CategoryId", "pvw_AbsenceType", "Id");
            CreateIndex("pvw_Absence", "StatusId");
            CreateIndex("pvw_Absence", "CategoryId");
            DropColumn("pvw_Absence", "MainCategoryId");
            DropColumn("pvw_Absence", "SubCategoryId");
           ......
            Sql(@"
                                        SET IDENTITY_INSERT [dbo].[pvw_AbsenceStatusType] ON
                    INSERT pvw_AbsenceStatusType (Id, Name) VALUES (1, N'Entwurf')                       
                                        SET IDENTITY_INSERT [dbo].[pvw_AbsenceStatusType] OFF
            ");    
            .....
        }

        public override void Down()
        {
            ........
        }