在 Entity Framework 6 中仅将现有数据库映射到现有 POCO，无需设计器或 CodeFirst

Question

@slauma 在 cmets 中给出的一个重要事实。所以看看答案和 cmets！

我正在尝试在 EF6 中使用实际与 NHibernate 一起使用的组件。问题是，我有一些带有不同名称主键的 TPT 继承。给出了数据库和 POCO 类，我无法更改它们中的任何一个，因此 CodeFirst 和 EF 设计器都没有问题。

有没有办法将现有 Db 映射到现有 POCO 类，就像您在 NHibernate 中使用这些 .hbm.xml 映射文件一样？

更新：

我遇到的实际问题首先是几个类的TPT映射，其中这些类的主键名称不同，代码优先似乎不支持。

比如：

public class Record
{
  public virtual int Ndx { get; set; }  // table column 'ndx'

  public virtual DateTime CreatedAt { get; set; }  // table column 'created'

  // ... further properties
}

public class Patient : Record
{
  public virtual int RecordNdx {get; set;}  // table column 'record_ndx) with FK => records.ndx

  // ... further properties
}

如前所述，更改属性或列名不是一种选择。

更新二：

这是我的注册码：

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    modelBuilder.Entity<Record>()
        .ToTable("record_descriptors", "schema");

    modelBuilder.Entity<Record>()
        .HasKey<int>(e => e.ndx);

    modelBuilder.Entity<Record>()
        .Property(e => e.read_flag)
        .IsFixedLength()
        .IsUnicode(false);

    modelBuilder.Entity<Record>()
        .Property(e => e.row_version)
        .IsFixedLength();

    modelBuilder.Entity<Record>()
        .Property(e => e.update_info)
        .IsUnicode(false);

    modelBuilder.Entity<Patient>()
        .ToTable("patienten", "schema");

    modelBuilder.Entity<Patient>()
        .Property(e => e.mpi)
        .IsUnicode(false);

    modelBuilder.Entity<Patient>()
        .Property(e => e.ndx)
        .HasColumnName("record_ndx");

    modelBuilder.Entity<Patient>()
        .Ignore(r => r.RecordNdx);
}

更新 III

为了测试我使用：

db.patients.First(p => p.Ndx == 6040);

这会产生以下 SQL（由于真实记录和患者类而更广泛）：

SELECT 
    [Limit1].[C1] AS [C1], 
    [Limit1].[ndx] AS [ndx], 
    [Limit1].[owner_user_object_ndx] AS [owner_user_object_ndx], 
    [Limit1].[creator_department_user_object_ndx] AS [creator_department_user_object_ndx], 
    [Limit1].[creator_user_user_object_ndx] AS [creator_user_user_object_ndx], 
    [Limit1].[created] AS [created], 
    [Limit1].[read_flag] AS [read_flag], 
    [Limit1].[last_update] AS [last_update], 
    [Limit1].[last_update_user] AS [last_update_user], 
    [Limit1].[last_update_department] AS [last_update_department], 
    [Limit1].[freitext] AS [freitext], 
    [Limit1].[row_version] AS [row_version], 
    [Limit1].[update_info] AS [update_info], 
    [Limit1].[mpi] AS [mpi]
    FROM ( SELECT TOP (1) 
        [Extent1].[ndx] AS [ndx], 
        [Extent1].[mpi] AS [mpi], 
        [Extent2].[owner_user_object_ndx] AS [owner_user_object_ndx], 
        [Extent2].[creator_department_user_object_ndx] AS [creator_department_user_object_ndx], 
        [Extent2].[creator_user_user_object_ndx] AS [creator_user_user_object_ndx], 
        [Extent2].[created] AS [created], 
        [Extent2].[read_flag] AS [read_flag], 
        [Extent2].[last_update] AS [last_update], 
        [Extent2].[last_update_user] AS [last_update_user], 
        [Extent2].[last_update_department] AS [last_update_department], 
        [Extent2].[freitext] AS [freitext], 
        [Extent2].[row_version] AS [row_version], 
        [Extent2].[update_info] AS [update_info], 
        '0X0X' AS [C1]
        FROM  [schema].[patienten] AS [Extent1]
        INNER JOIN [schema].[record_descriptors] AS [Extent2] ON [Extent1].[ndx] = [Extent2].[ndx]
        WHERE 6040 = [Extent1].[ndx]
    )  AS [Limit1]

这是错误的，因为它从[patienten] 中选择[ndx]（必须是record_ndx）并尝试加入[ndx]

Answer 1

关于关闭this work item at CodePlex 的评论声称自 EF 6 在 TPT 映射中定义父实体和子实体的不同键列名称适用于 Code-First。如果这是真的，那么以下 Code-First 映射应该允许映射您的模型和数据库：

modelBuilder.Entity<Record>()
    .ToTable("YourRecordTableName");

modelBuilder.Entity<Record>()
    .HasKey(r => r.Ndx);

modelBuilder.Entity<Record>()
    .Property(r => r.Ndx)
    .HasColumnName("ndx"); // probably redundant because case doesn't matter

modelBuilder.Entity<Record>()
    .Property(r => r.CreatedAt)
    .HasColumnName("created");

modelBuilder.Entity<Patient>()
    .ToTable("YourPatientTableName");

modelBuilder.Entity<Patient>()
    .Property(r => r.Ndx)   // Yes, no typo: It must be Ndx, NOT RecordNdx !
    .HasColumnName("record_ndx");

modelBuilder.Entity<Patient>()
    .Ignore(r => r.RecordNdx);

最后一个映射（忽略RecordNdx 属性）很重要。这意味着您的关键属性将是Patient.Ndx。我认为您不能将派生类中的任何属性设为关键属性。关键属性必须始终位于继承层次结构的基类中。但是，此属性可以映射两次（或通常在 TPT 继承链中的每个实体一次）映射到每个表的不同列名 - 从 EF 6 开始。

完全摆脱RecordNdx 属性将是最干净的解决方案。但是，既然您说您不能触摸您的属性，那么将RecordNdx 的值与Ndx 属性耦合至少是有意义的（如果您可以更改属性获取器和设置器） ：

public virtual int RecordNdx
{
    get { return Ndx; }
    set { Ndx = value; }
}

编辑

我刚刚使用 EF 6.1 测试了上面的 Code-First 映射，它确实有效！ Record 表中的主键列是 ndx，Patient 表中的主键列是 record_ndx。在这些 EF 之间创建了 TPT 映射所需的一对一关系。

编辑 2

这是我用过的完整测试程序（当前 EF 6.1 Nuget 包，.NET 4.5，VS 2012，SQL Server 2012 Express）：

using System;
using System.Data.Entity;

namespace EFTPT6
{
    public class Record
    {
        public virtual int Ndx { get; set; }
        public virtual DateTime CreatedAt { get; set; }
    }

    public class Patient : Record
    {
        public virtual int RecordNdx { get; set; }
        public virtual string Name { get; set; }
    }

    public class MyContext : DbContext
    {
        public DbSet<Record> Records { get; set; }

        protected override void OnModelCreating(DbModelBuilder modelBuilder)
        {
            modelBuilder.Entity<Record>()
                .ToTable("Records");

            modelBuilder.Entity<Record>()
                .HasKey(r => r.Ndx);

            modelBuilder.Entity<Record>()
                .Property(r => r.Ndx)
                .HasColumnName("ndx");

            modelBuilder.Entity<Record>()
                .Property(r => r.CreatedAt)
                .HasColumnName("created");

            modelBuilder.Entity<Patient>()
                .ToTable("Patients");

            modelBuilder.Entity<Patient>()
                .Property(r => r.Ndx)
                .HasColumnName("record_ndx");

            modelBuilder.Entity<Patient>()
                .Ignore(p => p.RecordNdx);
        }
    }

    class Program
    {
        static void Main(string[] args)
        {
            Database.SetInitializer(new DropCreateDatabaseAlways<MyContext>());
            using (var ctx = new MyContext())
            {
                ctx.Database.Initialize(true);
                string sql = ctx.Records.ToString();
            }
        }
    }
}

程序末尾的字符串sql是：

SELECT 
    CASE WHEN ( NOT (([Project1].[C1] = 1) AND ([Project1].[C1] IS NOT NULL)))
        THEN '0X'
        ELSE '0X0X'
    END AS [C1], 
    [Extent1].[ndx] AS [ndx], 
    [Extent1].[created] AS [created], 
    CASE WHEN ( NOT (([Project1].[C1] = 1) AND ([Project1].[C1] IS NOT NULL)))
        THEN CAST(NULL AS varchar(1))
        ELSE [Project1].[Name]
    END AS [C2]
    FROM  [dbo].[Records] AS [Extent1]
    LEFT OUTER JOIN  (SELECT 
        [Extent2].[record_ndx] AS [record_ndx], 
        [Extent2].[Name] AS [Name], 
        cast(1 as bit) AS [C1]
        FROM [dbo].[Patients] AS [Extent2] ) AS [Project1]
            ON [Extent1].[ndx] = [Project1].[record_ndx]

看起来映射受到尊重，即Records 和Patients 表由ndx 和record_ndx 列连接。

编辑 3

重要的是上下文类不包含派生实体的集合，即没有public DbSet<Patient> Patients { get; set; }。如果确实如此，则忽略映射 modelBuilder.Entity<Patient>().Property(r => r.Ndx).HasColumnName("record_ndx");，并且 EF 预计 Patient 中的主键名称是 ndx 而不是 record_ndx。例如上面 SQL 的最后一行变成了ON [Extent1].[ndx] = [Project1].[ndx]。