我正在使用 Entity Framework 7 和代码优先,我有一个涉及 3 个级别的父子关系的模型:
Corporations
有公司
Companies
属于corporation
并且有factory
工厂
属于公司
由于这 3 个实体有很多共同点,它们都继承自一个抽象的 BaseOrganization
实体。
当我尝试列出所有工厂,包括它们的母公司,然后包括它们的母公司时,我有以下两种不同的情况:
- 不包含
BaseOrganization
到上下文中,代码优先创建三个表(对应于Table-Per-Concrete -类型或 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,code-first 创建带有鉴别器字段的一个表(对应于表-按层次结构或 TPH 模式)。Include()
和ThenInclude()
抛出一个Sequence contains more than one matching element
异常。
此问题(没有继承和抽象基类模式)已在 EF7 Github 存储库中得到解决,并已被清除(参见 https://github.com/aspnet/EntityFramework/issues/1460)。
所以我目前不知道我的方法是否有问题,或者这是否明显是 EF7 RC1 的问题?请注意,我真的更喜欢保留继承,以便我的 SQL 模型更具可读性。
下面是完整的复制代码:
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"
更新
如我自己的评论所述,我的第一个解决方法是避免在 DbContext 中包含基本类型,以便代码优先生成具有 TPC 模式的模式(错误仅在 TPH 策略中抛出)。
问题是上面的示例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(还?)不支持多对多关系,我们必须定义一个链接实体,它自己映射两个一对多关系。
在基类型级别定义和使用的映射实体,代码优先仍然选择 TPH 策略,然后错误仍然抛出。
换句话说,我被卡住了,或者我将不得不重复一些逻辑三次,这几乎就像故意打断自己的腿一样!
最佳答案
我认为您不应该尝试在您的案例中使用基类。
组织、公司、工厂代表不同的对象,从我在这里看到的情况来看,您正在尝试重构代码而不是抽象对象:
如果您创建一个存储作者和书籍的数据库,那么作者和书籍都会有一个名称和一个 ID,但是有一个基类有意义吗?
你肯定会节省几行代码,但它会降低你的代码可读性。
我认为当有真正的继承时你应该使用基类:
例如,您可以有一个基类 Person
和一个 Manager
和 Employee
类继承自 Person 类,因为员工和经理是人。
对我来说,你只需要删除你的基类,它就会按预期工作:
public class Corporation
{
public int Id { get; set; }
public string Name { get; set; }
public List<Company> Companies { get; set; } = new List<Company>();
}
public class Company
{
public int Id { get; set; }
public string Name { get; set; }
public Corporation Corporation { get; set; }
public List<Factory> Factories { get; set; } = new List<Factory>();
}
public class Factory
{
public int Id { get; set; }
public string Name { get; set; }
public Company Company { get; set; }
}
public class MyContext : DbContext
{
public DbSet<Corporation> Corporations { get; set; }
public DbSet<Company> Companies { get; set; }
public DbSet<Factory> Factories { get; set; }
...
protected override void OnModelCreating(ModelBuilder 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);
}
}
关于c# - Include() ThenInclude() 在 Table Per Hierarchy 策略中抛出 "Sequence contains more than one matching element"异常,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/36554296/