如何将新表中的新外键添加到现有记录

Question

使用 C# MVC 和实体框架 v6.2.0

我有一个现有的模型，Caller

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

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

我创建了一个新模型，LanguageChoice

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

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

我想将这个新的LanguageChoice 添加到Caller

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

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

    public Guid LanguageChoice_Id { get; set; } // <----

    [ForeignKey("LanguageChoice_Id")]
    public LanguageChoice LanguageChoice { get; set; } // <----
}

我这样做是因为它将在我的 ViewModel 中成为 IEnumerable<SelectListItem>。

在我的数据库中，我已有 Caller 记录：

╔═════════════════════╦═══════════╗
║         Id          ║ FirstName ║
╠═════════════════════╬═══════════╣
║ caller_guid_value_1 ║ Ryan      ║
║ caller_guid_value_2 ║ John      ║
╚═════════════════════╩═══════════╝

当我添加LanguageChoice 时，预期的结果将是：

╔═════════════════════╦═══════════╦═════════════════════════════╗
║         Id          ║ FirstName ║      LanguageChoice_Id      ║
╠═════════════════════╬═══════════╬═════════════════════════════╣
║ caller_guid_value_1 ║ Ryan      ║ languageChoice_guid_value_1 ║
║ caller_guid_value_2 ║ John      ║ languageChoice_guid_value_1 ║
╚═════════════════════╩═══════════╩═════════════════════════════╝

这是我的迁移：

public partial class AddCallerLanguageChoice : DbMigration
{
    public override void Up()
    {
        CreateTable(
            "dbo.LanguageChoices",
            c => new
                {
                    Id = c.Guid(nullable: false, identity: true),
                    Name = c.String(nullable: false, maxLength: 50),
                })
            .PrimaryKey(t => t.Id);

        AddColumn("dbo.Callers", "LanguageChoice_Id", c => c.Guid(nullable: false));
        CreateIndex("dbo.Callers", "LanguageChoice_Id");
        AddForeignKey("dbo.Callers", "LanguageChoice_Id", "dbo.LanguageChoices", "Id", cascadeDelete: true);
    }

    public override void Down()
    {
        DropForeignKey("dbo.Callers", "LanguageChoice_Id", "dbo.LanguageChoices");
        DropIndex("dbo.Callers", new[] { "LanguageChoice_Id" });
        DropColumn("dbo.Callers", "LanguageChoice_Id");
        DropTable("dbo.LanguageChoices");
    }
}

这是我的错误：

ALTER TABLE 语句与 FOREIGN KEY 约束“FK_dbo.Callers_dbo.LanguageChoices_LanguageChoice_Id”冲突。冲突发生在数据库“aspnet-My Web App-20171030040324”、表“dbo.LanguageChoices”、“Id”列中。

有没有办法做到这一点，还是我应该继续允许LanguageChoice_Id 可以为空？

---

4年前的类似问题：Entity Framework The ALTER TABLE statement conflicted with the FOREIGN KEY constraint

• 4 岁，也许从那以后发生了一些变化
• 他们使用 int 值作为 Id，我使用 Guid，所以我无法提前猜测/假设 Id 值
• 我想避免创建一个迁移，其中LanguageChoice_Id 可以为空，然后是更新记录的种子方法，然后是另一个使LanguageChoice_Id 不可为空的迁移，因为在将两个迁移都推送到 Azure 时会中断种子方法将最后运行。 （参见 Ari Roth 对 RicklsWright 回答的评论）

---

更新：

按照@henoc salinas'更新的答案，我来到了这个可行的迁移文件。

Henoc 的答案是公认的答案，这只是为了展示我最终得到的结果，不同之处在于我在此处插入了表值并使用非临时值更新了 Caller 的空值：

        public override void Up()
    {
        CreateTable(
            "dbo.LanguageChoices",
            c => new
                {
                    Id = c.Guid(nullable: false, identity: true),
                    Name = c.String(nullable: false, maxLength: 50),
                })
            .PrimaryKey(t => t.Id);

        Sql(String.Format("INSERT INTO LanguageChoices VALUES ('{0}','{1}')", Guid.NewGuid(), "English"));
        Sql(String.Format("INSERT INTO LanguageChoices VALUES ('{0}','{1}')", Guid.NewGuid(), "Other"));
        Sql(String.Format("INSERT INTO LanguageChoices VALUES ('{0}','{1}')", Guid.NewGuid(), "Spanish"));

        AddColumn("dbo.Callers", "LanguageChoice_Id", c => c.Guid(nullable: true));

        Sql("UPDATE Callers Set LanguageChoice_Id = (SELECT Id FROM LanguageChoices WHERE Name = \'English\') WHERE LanguageChoice_Id IS NULL");

        AlterColumn("dbo.Callers", "LanguageChoice_Id", c => c.Guid(nullable: false));

        CreateIndex("dbo.Callers", "LanguageChoice_Id");
        AddForeignKey("dbo.Callers", "LanguageChoice_Id", "dbo.LanguageChoices", "Id", cascadeDelete: true);
    }

    public override void Down()
    {
        DropForeignKey("dbo.Callers", "LanguageChoice_Id", "dbo.LanguageChoices");
        DropIndex("dbo.Callers", new[] { "LanguageChoice_Id" });
        DropColumn("dbo.Callers", "LanguageChoice_Id");
        DropTable("dbo.LanguageChoices");
    }
}

Answer 1

产生这个冲突是因为新表LanguageChoices在创建时没有元素，所以外键因为不可为空而没有找到有效值，你可以试试改变：

 public Guid LanguageChoice_Id { get; set; }

到这里：

  public Guid? LanguageChoice_Id { get; set; }

然后再次生成迁移，你可以看到这一行：

 AddColumn("dbo.Callers", "LanguageChoice_Id", c => c.Guid(nullable: false));

改成这样：

 AddColumn("dbo.Callers", "LanguageChoice_Id", c => c.Guid());

现在，您可以更新数据库，并将列更改为不为空，添加有效值并再次更改该行，然后生成新的迁移：

public Guid? LanguageChoice_Id { get; set; }

到：

public Guid LanguageChoice_Id { get; set; }

在您发表评论之后

在标记上插入 sql 代码：

public partial class AddCallerLanguageChoice : DbMigration
{
    public override void Up()
    {
        CreateTable(
            "dbo.LanguageChoices",
            c => new
                {
                    Id = c.Guid(nullable: false, identity: true),
                    Name = c.String(nullable: false, maxLength: 50),
                })
            .PrimaryKey(t => t.Id);

        string TempKey = Guid.NewGuid ( ).ToString();
        this.Sql ( String.Format ( "Insert into dbo.LanguageChoices values ({0},{1})", TempKey, "Initial" ) );

        AddColumn("dbo.Callers", "LanguageChoice_Id", c => c.Guid(nullable: false));

        Sql ( String.Format ( "Update dbo.Callers set LanguageChoice_Id='{0}' where LanguageChoice_Id is null", TempKey ) );

        CreateIndex("dbo.Callers", "LanguageChoice_Id");
        AddForeignKey("dbo.Callers", "LanguageChoice_Id", "dbo.LanguageChoices", "Id", cascadeDelete: true);
    }

    public override void Down()
    {
        DropForeignKey("dbo.Callers", "LanguageChoice_Id", "dbo.LanguageChoices");
        DropIndex("dbo.Callers", new[] { "LanguageChoice_Id" });
        DropColumn("dbo.Callers", "LanguageChoice_Id");
        DropTable("dbo.LanguageChoices");
    }
}