c# - Entity Framework 迁移，对现有数据进行非规范化并引入外键

我有一个现有的数据库（首先是EF代码），该数据库的表（table1）中的数据表示一个枚举（c＃），然后另一个表（table2）的一个列包含该枚举的值之一。

我需要做的是对table1进行非规范化，以便它具有table2的外键（枚举值）

关于实体，我从开始：

public class EnvironmentTypes
{
    [Key]
    public int EnvironmentTypeId { get; set; }

    [Required]
    [MaxLength(100)]
    public string Name { get; set; }

    [Required]
    [MaxLength(200)]
    public string Description { get; set; }
}

对于table1

和

public class EnvironmentDetails
{
    [Required]
    [Index("IX_AppUserMachine", 1, IsUnique = true)]
    [MaxLength(200)]
    public string ApplicationName { get; set; }

    [Index("IX_AppUserMachine", 2, IsUnique = true)]
    [MaxLength(200)]
    public string MachineName { get; set; }

    [Index("IX_AppUserMachine", 3, IsUnique = true)]
    [MaxLength(50)]
    public string UserName { get; set; }

    [Required]
    public EnvironmentType EnvironmentType { get; set; }
}

对于table2

更改之后，我需要使table2的实体变为

public class EnvironmentDetails
{
    [Required]
    [Index("IX_AppUserMachine", 1, IsUnique = true)]
    [MaxLength(200)]
    public string ApplicationName { get; set; }

    [Index("IX_AppUserMachine", 2, IsUnique = true)]
    [MaxLength(200)]
    public string MachineName { get; set; }

    [Index("IX_AppUserMachine", 3, IsUnique = true)]
    [MaxLength(50)]
    public string UserName { get; set; }

    [Required]
    [ForeignKey(nameof(EnvironmentTypeId))]
    public virtual EnvironmentTypes EnvironmentType { get; set; }

    public int EnvironmentTypeId { get; set; }
}

创建迁移将提供：

public partial class DenormaliseEnvironmentTypeFromEnvironmentDetails : DbMigration
{
    public override void Up()
    {
        AddColumn("dbo.EnvironmentDetails", "EnvironmentTypeId", c => c.Int(nullable: false);
        CreateIndex("dbo.EnvironmentDetails", "EnvironmentTypeId");
        AddForeignKey("dbo.EnvironmentDetails", "EnvironmentTypeId", "dbo.EnvironmentTypes", "EnvironmentTypeId", cascadeDelete: true);
        DropColumn("dbo.EnvironmentDetails", "EnvironmentType");
    }

    public override void Down()
    {
        AddColumn("dbo.EnvironmentDetails", "EnvironmentType", c => c.Int(nullable: false));
        DropForeignKey("dbo.EnvironmentDetails", "EnvironmentTypeId", "dbo.EnvironmentTypes");
        DropIndex("dbo.EnvironmentDetails", new[] { "EnvironmentTypeId" });
        DropColumn("dbo.EnvironmentDetails", "EnvironmentTypeId");
    }
}

对于空数据库，它工作正常，但是如果我在table2中有数据，则运行迁移会引发与外键约束有关的错误。

我的想法是，我应该根据之前的数据填充新的EnvironmentTypeId列，因此我尝试修改迁移，以向defaultValueSql添加ColumnBuilder参数：

AddColumn("dbo.EnvironmentDetails", "EnvironmentTypeId", c => c.Int(nullable: false, defaultValueSql: "(select [EnvironmentTypeId] from [dbo].[EnvironmentTypes] where [dbo].[EnvironmentTypes].[EnumId] = [EnvironmentType])"));

但这给出了错误

Error Number:1046,State:1,Class:15
Subqueries are not allowed in this context. Only scalar expressions are allowed.

有什么方法可以执行此迁移而不会丢失数据（或完整性）

最佳答案

借助于@Александр-Пашкин的答案，我设法手动修改了迁移以维护现有数据。我最终使用的迁移看起来像：

CreateTable("tmp", c => new
{
    DetailsId = c.Int(),
    TypeId = c.Int()
});
Sql("INSERT INTO [dbo].[tmp] select d.Id as DetailsId, t.EnvironmentTypeId as TypeId from [dbo].[EnvironmentDetails] d inner join [dbo].[EnvironmentTypes] t on d.EnvironmentType = t.EnumId");
AddColumn("dbo.EnvironmentDetails", "EnvironmentTypeId", c => c.Int(nullable: false, defaultValue: 1));
CreateIndex("dbo.EnvironmentDetails", "EnvironmentTypeId");
AddForeignKey("dbo.EnvironmentDetails", "EnvironmentTypeId", "dbo.EnvironmentTypes", "EnvironmentTypeId", cascadeDelete: true);
DropColumn("dbo.EnvironmentDetails", "EnvironmentType");
Sql("UPDATE [dbo].[EnvironmentDetails] SET [EnvironmentTypeId] = (SELECT t.[TypeId] from [dbo].[tmp] t where t.DetailsId = Id)");
DropTable("tmp");

因此需要创建一个临时表来根据当前数据保存表之间的链接

根据需要修改数据模型

然后从临时表填充现有的table2

最后删除临时表。

关于c# - Entity Framework 迁移，对现有数据进行非规范化并引入外键，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/40151940/