Entity Framework 将外键设置为可为空后，代码首先无法更新数据库

Question

在我将模型的外键（ProcessID 和 SubProcessID）设置为可为 null 后，我无法先使用 EF 代码更新我的数据库。

这是模型：

public class MyModel
{
    [DatabaseGenerated(DatabaseGeneratedOption.Identity)]
    public long MyModelID { get; set; }

    [Display(Name = "Process")]
    public int? ProcessID { get; set; }

    [Display(Name = "Sub Process")]
    public int? SubProcessID { get; set; }

    //... some more properties here

    public virtual Process Process { get; set; }
    public virtual SubProcess SubProcess { get; set; }
}

添加迁移后的迁移代码如下：

public override void Up()
{
    DropForeignKey("dbo.MyTable", "ProcessID", "dbo.Process");
    DropForeignKey("dbo.MyTable", "SubProcessID", "dbo.SubProcess");
    DropIndex("dbo.MyTable", new[] { "ProcessID" });
    DropIndex("dbo.MyTable", new[] { "SubProcessID" });
    AlterColumn("dbo.MyTable", "ProcessID", c => c.Int());
    AlterColumn("dbo.MyTable", "SubProcessID", c => c.Int());
    CreateIndex("dbo.MyTable", "ProcessID");
    CreateIndex("dbo.MyTable", "SubProcessID");
    AddForeignKey("dbo.MyTable", "ProcessID", "dbo.Process", "ProcessID");
    AddForeignKey("dbo.MyTable", "SubProcessID", "dbo.SubProcess", "SubProcessID");
}

public override void Down()
{
    DropForeignKey("dbo.MyTable", "SubProcessID", "dbo.SubProcess");
    DropForeignKey("dbo.MyTable", "ProcessID", "dbo.Process");
    DropIndex("dbo.MyTable", new[] { "SubProcessID" });
    DropIndex("dbo.MyTable", new[] { "ProcessID" });
    AlterColumn("dbo.MyTable", "SubProcessID", c => c.Int(nullable: false));
    AlterColumn("dbo.MyTable", "ProcessID", c => c.Int(nullable: false));
    CreateIndex("dbo.MyTable", "SubProcessID");
    CreateIndex("dbo.MyTable", "ProcessID");
    AddForeignKey("dbo.MyTable", "SubProcessID", "dbo.SubProcess", "SubProcessID", cascadeDelete: true);
    AddForeignKey("dbo.MyTable", "ProcessID", "dbo.Process", "ProcessID", cascadeDelete: true);
}

我收到的错误消息是这样的：

Table 'MyDatabase.dbo.MyTable' doesn't exist

注意： 我只是在将这些外键设置为可为空的 int 时更新数据库失败。但是，如果我将其设为 int，则可以成功更新数据库。

感谢您的帮助！

Answer 1

如果你们中的任何人遇到与我相同的问题，这是我对我的问题的解决方案：

在“迁移”文件夹中> Configuration.cs：

我将配置构造函数更改为：

public Configuration()
{
    AutomaticMigrationsEnabled = false;
    SetSqlGenerator("MySql.Data.MySqlClient", new MySql.Data.Entity.MySqlMigrationSqlGenerator());
    CodeGenerator = new MySql.Data.Entity.MySqlMigrationCodeGenerator();
}

现在可以更新数据库了！！

如果你们中的任何人在使用 MySQL 使用代码优先方法时遇到问题，我愿意提供帮助！ :)

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