c# – Include()ThenInclude()在Table Per Hierarchy策略中抛出

>公司有公司
>公司属于公司并拥有工厂
>工厂属于一家公司

由于这3个实体共享很多共同点,因此它们都从一个抽象的BaSEOrganization实体继承.

当我试图列出所有工厂,包括他们的母公司,然后包括他们的母公司时,我有这两种不同的情况：

>不将BaSEOrganization包含到上下文中,代码优先创建三个表(对应于Table-Per-Concrete-Type或TPC模式). Include()和ThenInclude()工作正常,我可以按预期列出工厂和遍历关系.
>将BaSEOrganization包含到上下文中,代码优先创建一个带有鉴别器字段的表(对应于Table-Per-Hierarchy或TPH模式). Include()和ThenInclude()抛出一个包含多个匹配元素异常的Sequence.

这个问题(没有继承和抽象基类模式)已经在EF7 Github repo中得到了解决,并且已被清除(见https://github.com/aspnet/EntityFramework/issues/1460).

所以我目前不知道我的方法是否有问题,或者这显然是EF7 RC1的问题？请注意,我更喜欢保持继承,以便我的SQL模型更具可读性.

以下是完整的复制代码：

using System;
    using System.Collections.Generic;
    using System.Linq;
    using Microsoft.Data.Entity;

    namespace MultiLevelTest
    {
        // All places share name and Id
        public abstract class BaSEOrganization
        {
            public int Id { get; set; }
            public string Name { get; set; }
        }

        // a corporation (eg : Airbus Group)
        public class Corporation : BaSEOrganization
        {
            public virtual ICollection<Company> Companies { get; set; } = new List<Company>();
        }

        // a company (eg : Airbus,Airbus Helicopters,Arianespace)
        public class Company : BaSEOrganization
        {
            public virtual Corporation Corporation { get; set; }
            public virtual ICollection<Factory> Factories { get; set; } = new List<Factory>();
        }

        // a factory of a company (Airbus Toulouse,Airbus US...)
        public class Factory : BaSEOrganization
        {
            public virtual Company Company { get; set; }
        }

        // setup DbContext
        public class MyContext : DbContext
        {
            // if this line is commented,then code first creates 3 tables instead of one,and everything works fine.
            public DbSet<BaSEOrganization> BaSEOrganizationCollection { get; set; }
            public DbSet<Corporation> Corporations { get; set; }
            public DbSet<Company> Companies { get; set; }
            public DbSet<Factory> Factories { get; set; }

            protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
            {
                optionsBuilder.UseSqlServer(
                    @"Server=(localdb)mssqllocaldb;Database=MultiLevelTest;Trusted_Connection=True;MultipleActiveResultSets=true");
            }

            protected override void OnModelCreating(ModelBuilder modelBuilder)
            {
                base.OnModelCreating(modelBuilder);

                modelBuilder.Entity<Corporation>().HasMany(c => c.Companies).WithOne(c => c.Corporation);
                modelBuilder.Entity<Company>().HasMany(c => c.Factories).WithOne(c => c.Company);
                modelBuilder.Entity<Factory>().HasOne(f => f.Company);
            }
        }

        public class Program
        {
            public static void Main(string[] args)
            {
                using (var ctx = new MyContext())
                {
                    ctx.Database.EnsureDeleted();
                    ctx.Database.EnsureCreated();

                    // Add a corporation with companies then factories (this works fine)
                    if (!ctx.Corporations.Any()) CreateOrganizationGraph(ctx);

                    // Get all the factories without including anything (this is still working fine)
                    var simpleFactories = ctx.Factories.ToList();
                    foreach(var f in simpleFactories) Console.WriteLine(f.Name);

                    // Get all the factories including their mother company,then their mother corporation
                    var fullFactories = ctx.Factories
                        .Include(f => f.Company)
                        .ThenInclude(c => c.Corporation)
                        .ToList();
                    foreach (var f in fullFactories) Console.WriteLine($"{f.Company.Corporation.Name} > {f.Company.Name} > {f.Name}");
                }
            }

            public static void CreateOrganizationGraph(MyContext ctx)
            {
                var airbusCorp = new Corporation()
                {
                    Name = "Airbus Group",Companies = new List<Company>()
                            {
                                new Company
                                {
                                    Name = "Airbus",Factories = new List<Factory>()
                                    {
                                        new Factory {Name = "Airbus Toulouse (FR)"},new Factory {Name = "Airbus Hambourg (DE)"}
                                    }
                                },new Company
                                {
                                    Name = "Airbus Helicopters",Factories = new List<Factory>()
                                    {
                                        new Factory {Name = "Eurocopter Marignane (FR)"},new Factory {Name = "Eurocopter Deutschland (DE)"}
                                    }
                                }
                            }
                };

                ctx.Corporations.Add(airbusCorp);
                ctx.SaveChanges();

            }
        }
    }

您将需要包含以下NuGet包：

"EntityFramework.Commands": "7.0.0-rc1-final","EntityFramework.Core": "7.0.0-rc1-final","EntityFramework.MicrosoftSqlServer": "7.0.0-rc1-final"

UPDATE

正如我自己的评论中所述,我的第一个解决方法是避免在DbContext中包含基类型,以便代码优先生成具有TPC模式的模式(只有在TPH策略中才会抛出错误).

问题是上面的例子比我的实际实现更简单,它涉及在基类型级别定义的多对多关系.

由于EF7不支持(但？)支持多对多关系,因此我们必须定义一个链接实体,该实体可以自己映射两个一对多关系.

该映射实体在基类型级别定义和使用,代码优先仍然选择TPH策略,然后仍然会抛出错误.

换句话说,我被卡住了,或者我将不得不重复一些逻辑三次,这几乎就像故意破坏我自己的腿！