实体框架迁移，取消现有数据的规范化并引入外键

本文关键字：规范化 数据 迁移 框架 取消 实体 | 更新日期: 2023-09-27 18:14:10

我有一个现有的数据库(首先是EF代码(，它在一个表(table1(中有数据，该表表示枚举(c#(，然后是另一个表的列(table2(，该表的列包含枚举的一个值。

我需要做的是去规范化table1，使其具有table2(枚举值(的外键

就我开始的实体而言：

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

在更改之后，我需要使table2的实体变成

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");
    }
}

这对于空数据库来说很好，但如果我在table2中有数据，那么运行迁移会抛出一个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，所以我试图修改迁移，在ColumnBuilder:中添加一个defaultValueSql参数

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

然而，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.

有没有任何方法可以在不丢失数据(或非法性(的情况下执行此迁移

实体框架迁移，取消现有数据的规范化并引入外键

在@Александр-Пашкин的回答的帮助下，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保存基于当前数据的表之间的链接

根据需要修改数据模型

则从临时表填充现有的CCD_ 12

终于放下了临时桌子。

您可以使用DbMigration的Sql方法并删除defaultValueSql

Sql("select [EnvironmentTypeId] from [dbo].[EnvironmentTypes] 
     where [dbo].[EnvironmentTypes].[EnumId] = [EnvironmentType]");
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