如何通过EF迁移将int ID列更改为Guid？

Question

我正在使用EF代码优先方法,并希望将Id字段更改为guid但似乎无法通过以下错误.

这是我的第一次迁移:

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");
    }
}

后来我意识到我需要我的Id列是GUID所以我改变了我的模型文件:

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; }
}

运行时Add-Migration ChangeDownloadTokenIdToGuid会生成以下文件:

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");
    }
}

运行此文件Update-Database会导致此错误:

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.

任何想法为什么会这样？

Answer 1

这是因为无法将以前int类型的Id列转换为Guid类型(完全是尝试执行AlterColumn方法).此外,错误消息建议您,新类型的Id列可以是set:int,bigint,smallint,tinyint或decimal的数字类型之一,其标度为0,对于它们,可以从int类型执行转换.

解决方案 - 只需删除Id列,然后使用新Guid类型重新创建它,以这种方式更改迁移:

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");
    }
}

PS为什么你使用DatabaseGeneratedOption.Computed属性,不是 DatabaseGeneratedOption.Identity？

Answer 2

即使Slava Utesinov的作品,它只适用于空表或没有其他表指的是您正在转换的表.因此,这个答案将帮助那些以更复杂的数据库设置结束此页面的人.

下面是您可以在迁移类中使用的实用程序函数,该函数应该从Up/Down函数调用.该函数还处理表引用您尝试从Int转换为Guid的表.此辅助函数假定您要转换的列称为"Id",但应该是相当通用的.

public void Convert(bool toGuid, string parent, params string[] children)
    {
        if (toGuid)
        {
            AddColumn($"dbo.{parent}s", "Id2", c => c.Guid(nullable: false, identity: true, defaultValueSql: "newid()"));
        }
        else
        {
            AddColumn($"dbo.{parent}s", "Id2", c => c.Int(nullable: false, identity: true));
        }
        foreach (var child in children)
        {
            DropForeignKey($"dbo.{child}s", $"{parent}_Id", $"dbo.{parent}s");
            DropIndex($"dbo.{child}s", new[] { $"{parent}_Id" });
            RenameColumn($"dbo.{child}s", $"{parent}_Id", $"old_{parent}_Id");
            if (toGuid)
            {
                AddColumn($"dbo.{child}s", $"{parent}_Id", c => c.Guid());
            }
            else
            {
                AddColumn($"dbo.{child}s", $"{parent}_Id", c => c.Int());
            }
            Sql($"update c set {parent}_Id=p.Id2 from {child}s c inner join {parent}s p on p.Id=c.old_{parent}_Id");
            DropColumn($"dbo.{child}s", $"old_{parent}_Id");
        }
        DropPrimaryKey($"dbo.{parent}s");
        DropColumn($"dbo.{parent}s", "Id");
        RenameColumn($"dbo.{parent}s", "Id2", "Id");
        AddPrimaryKey($"dbo.{parent}s", "Id");
        foreach (var child in children)
        {
            CreateIndex($"dbo.{child}s", $"{parent}_Id");
            AddForeignKey($"dbo.{child}s", $"{parent}_Id", $"dbo.{parent}s", "Id");
        }
    }

因此,在您的情况下,您的向上/向下功能将是:

    public override void Up()
    {
        Convert(true,"DownloadToken");
    }

    public override void Down()
    {
        Convert(false, "DownloadToken");
    }