karlingen karlingen - 3 months ago 35
ASP.NET (C#) Question

How can I change an int ID column to Guid with EF migration?

I'm using EF code-first approach and want to change the

Id
field to
guid
but can't seem to get past below error.

This is my first migration:

public partial class CreateDownloadToken : DbMigration
{
public override void Up()
{
CreateTable(
"dbo.DownloadTokens",
c => new
{
Id = c.Int(nullable: false, identity: true),
FileId = c.Int(),
UserId = c.String(nullable: false, maxLength: 128),
ValidUntil = c.DateTime(nullable: false),
})
.PrimaryKey(t => t.Id)
.ForeignKey("dbo.Files", t => t.FileId)
.ForeignKey("dbo.Users", t => t.UserId, cascadeDelete: true)
.Index(t => t.FileId)
.Index(t => t.UserId);

}

public override void Down()
{
DropForeignKey("dbo.DownloadTokens", "UserId", "dbo.Users");
DropForeignKey("dbo.DownloadTokens", "FileId", "dbo.Files");
DropIndex("dbo.DownloadTokens", new[] { "UserId" });
DropIndex("dbo.DownloadTokens", new[] { "FileId" });
DropTable("dbo.DownloadTokens");
}
}


Later I realized that I need my
Id
column to be GUID so I changed my model file:

public class DownloadToken
{
[Key, DatabaseGenerated(DatabaseGeneratedOption.Computed)]
public Guid Id { get; set; }

public int? FileId { get; set; }

[ForeignKey("FileId")]
public virtual File File { get; set; }

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

[ForeignKey("UserId")]
public virtual User User { get; set; }

[Required]
public DateTime ValidUntil { get; set; }
}


When running
Add-Migration ChangeDownloadTokenIdToGuid
it generates this file:

public partial class ChangeDownloadTokenIdToGuid : DbMigration
{
public override void Up()
{
DropPrimaryKey("dbo.DownloadTokens");
AlterColumn("dbo.DownloadTokens", "Id", c => c.Guid(nullable: false));
AddPrimaryKey("dbo.DownloadTokens", "Id");
}

public override void Down()
{
DropPrimaryKey("dbo.DownloadTokens");
AlterColumn("dbo.DownloadTokens", "Id", c => c.Int(nullable: false, identity: true));
AddPrimaryKey("dbo.DownloadTokens", "Id");
}
}


Running this file with
Update-Database
causes this error:

Identity column 'Id' must be of data type int, bigint, smallint, tinyint, or decimal or numeric with a scale of 0, and constrained to be nonnullable.


Any ideas why this might be happening?

Answer

It was caused because it is impossible to convert previous int type of Id column to Guid type(exactly that try to perform AlterColumn method). Also, error message suggest you, that new type of Id column can be one of type from set: int, bigint, smallint, tinyint, or decimal or numeric with a scale of 0, for them, it is possible to perform conversion from int type.

Solution - simply drop Id column and then recreate it with new Guid type, change migration that way:

public partial class ChangeDownloadTokenIdToGuid : DbMigration
{
    public override void Up()
    {
        DropPrimaryKey("dbo.DownloadTokens");

        DropColumn("dbo.DownloadTokens", "Id");
        AddColumn("dbo.DownloadTokens", "Id", c => c.Guid(nullable: false, identity: true));

        AddPrimaryKey("dbo.DownloadTokens", "Id");
    }

    public override void Down()
    {
        DropPrimaryKey("dbo.DownloadTokens");

        DropColumn("dbo.DownloadTokens", "Id");
        AddColumn("dbo.DownloadTokens", "Id", c => c.Int(nullable: false, identity: true));

        AddPrimaryKey("dbo.DownloadTokens", "Id");
    }
}

P.S. Why you use DatabaseGeneratedOption.Computed attribute, not DatabaseGeneratedOption.Identity?

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