entity-framework - 无法确定关系的主体端 - 多个添加的实体可能具有相同的主键

Question

我正在使用 Entity Framework 5 Code First，并且我有以下适用于汽车制造商、汽车和卡车的模型:

public class Manufacturer
{
    public int Id { get; set; }
    public string Name { get; set; }

    [ForeignKey("ManufacturerId")]
    public virtual List<Car> Cars { get; set; }
    [ForeignKey("ManufacturerId")]
    public virtual List<Truck> Trucks { get; set; }
}

public class Vehicle
{
    public int Id { get; set; }
    public string Colour { get; set; }
    public int ManufacturerId { get; set; }
    public virtual Manufacturer Manufacturer { get; set; }
}

public class Car : Vehicle
{ }

public class Truck : Vehicle
{ }

public class Context : DbContext
{
    public DbSet<Manufacturer> Manufacturers { get; set; }
    public DbSet<Vehicle> Vehicles { get; set; }
}

对于开发和测试，我将数据播种如下:

public class DbInitialiser : DropCreateDatabaseAlways<Context>
{
    protected override void Seed(Context context)
    {
        var manufacturers = new List<Manufacturer>
        { 
            new Manufacturer
                {
                    Name = "Test Manufacturer",
                    Cars = new List<Car>
                        {
                            new Car { Colour = "Blue" },
                            new Car { Colour = "Green" }
                        },
                    Trucks = new List<Truck>
                        {
                            new Truck { Colour = "Red" }
                        }
                },
            new Manufacturer
                {
                    Name = "Another Manufacturer",
                    Cars = new List<Car>
                        {
                            new Car { Colour = "Pink" }
                        }
                }
        };

        manufacturers.ForEach(x => context.Manufacturers.Add(x));
    }
}

但是，当我使用上下文时，出现以下异常:
无法确定“EF_Associations.Vehicle_Manufacturer”关系的主体端。多个添加的实体可能具有相同的主键。

堆栈跟踪:

System.Data.DataException was unhandled
HResult=-2146233087
Message=An exception occurred while initializing the database. See the InnerException for details.
Source=EntityFramework
StackTrace:
   at System.Data.Entity.Internal.InternalContext.PerformInitializationAction(Action action)
   at System.Data.Entity.Internal.InternalContext.PerformDatabaseInitialization()
   at System.Data.Entity.Internal.LazyInternalContext.<InitializeDatabase>b__4(InternalContext c)
   at System.Data.Entity.Internal.RetryAction`1.PerformAction(TInput input)
   at System.Data.Entity.Internal.LazyInternalContext.InitializeDatabaseAction(Action`1 action)
   at System.Data.Entity.Internal.LazyInternalContext.InitializeDatabase()
   at System.Data.Entity.Internal.InternalContext.Initialize()
   at System.Data.Entity.Internal.InternalContext.GetEntitySetAndBaseTypeForType(Type entityType)
   at System.Data.Entity.Internal.Linq.InternalSet`1.Initialize()
   at System.Data.Entity.Internal.Linq.InternalSet`1.GetEnumerator()
   at System.Data.Entity.Infrastructure.DbQuery`1.System.Collections.Generic.IEnumerable<TResult>.GetEnumerator()
   at EF_Associations.Program.Main(String[] args) in c:\temp\EF-Associations\Program.cs:line 19
   ...
InnerException: System.Data.Entity.Infrastructure.DbUpdateException
   HResult=-2146233087
   Message=Unable to determine the principal end of the 'EF_Associations.Vehicle_Manufacturer' relationship. Multiple added entities may have the same primary key.
   Source=EntityFramework
   StackTrace:
        at System.Data.Entity.Internal.InternalContext.SaveChanges()
        at System.Data.Entity.Internal.LazyInternalContext.SaveChanges()
        at System.Data.Entity.DbContext.SaveChanges()
        at System.Data.Entity.DropCreateDatabaseAlways`1.InitializeDatabase(TContext context)
        at System.Data.Entity.Database.<>c__DisplayClass2`1.<SetInitializerInternal>b__0(DbContext c)
        at System.Data.Entity.Internal.InternalContext.<>c__DisplayClass8.<PerformDatabaseInitialization>b__6()
        at System.Data.Entity.Internal.InternalContext.PerformInitializationAction(Action action)
   InnerException: System.Data.UpdateException
        HResult=-2146233087
        Message=Unable to determine the principal end of the 'EF_Associations.Vehicle_Manufacturer' relationship. Multiple added entities may have the same primary key.
        Source=System.Data.Entity
        StackTrace:
             at System.Data.Mapping.Update.Internal.UpdateTranslator.RegisterEntityReferentialConstraints(IEntityStateEntry stateEntry, Boolean currentValues)
             at System.Data.Mapping.Update.Internal.UpdateTranslator.RegisterReferentialConstraints(IEntityStateEntry stateEntry)
             at System.Data.Mapping.Update.Internal.UpdateTranslator.PullModifiedEntriesFromStateManager()
             at System.Data.Mapping.Update.Internal.UpdateTranslator.ProduceCommands()
             at System.Data.Mapping.Update.Internal.UpdateTranslator.Update(IEntityStateManager stateManager, IEntityAdapter adapter)
             at System.Data.EntityClient.EntityAdapter.Update(IEntityStateManager entityCache)
             at System.Data.Objects.ObjectContext.SaveChanges(SaveOptions options)
             at System.Data.Entity.Internal.InternalContext.SaveChanges()
        InnerException: 

我将如何指定这种关系的主要结束点？

我尝试通过模型构建器 fluent API 添加以下配置，但没有成功:

protected override void OnModelCreating(DbModelBuilder modelBuilder)
{
    modelBuilder.Entity<Vehicle>()
        .HasRequired(v => v.Manufacturer)
        .WithRequiredDependent();
}

Answer 1

您的制造商类中必须只有一个外键属性:Vehicles。

[ForeignKey("ManufacturerId")]
public virtual List<Vehicle> Vehicles { get; set; }

您必须修改您的种子方法以使用这个单一的 FK 属性。 EF 将创建一个从实体类的继承链推断出的每个层次结构的表模型:

protected override void Seed(Context context)
{
    var manufacturers = new List<Manufacturer>
    { 
        new Manufacturer
            {
                Name = "Test Manufacturer",
                Vehicles = new List<Vehicle>
                    {
                        new Car {Colour = "Blue" },
                        new Car {Colour = "Green" },
                        new Truck {Colour = "Red" }
                    }
            },
        new Manufacturer
            {
                Name = "Another Manufacturer",
                Vehicles = new List<Vehicle>
                    {
                        new Car {Colour = "Pink" }
                    }
            }
    };

    manufacturers.ForEach(x => context.Manufacturers.Add(x));
    context.SaveChanges();
}

按照惯例，EF 将生成一个额外的 鉴别器 列的值取自您的 中的子类名称( Car , Truck )车辆 table 。

为方便起见，您可以在制造商上创建两个额外的(非 FK)属性，每个属性都包含一个特定于继承的 OfType询问:

public IEnumerable<Car> Cars
{
    get
    {
        return this.Vehicles.OfType<Car>();
    }
}

public IEnumerable<Truck> Trucks
{
    get
    {
        return this.Vehicles.OfType<Truck>();
    }
}

并使用它们来查询:

using (var db = new Context())
{
    foreach (var manufacturer in db.Manufacturers)
    {
        var cars = manufacturer.Cars.ToList();
        var trucks = manufacturer.Trucks.ToList();
    }
}