Question

我正在使用Entity Framework 5 Code First，我对汽车制造商，汽车和卡车有以下型号：

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，我按如下方式播种数据：

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，我得到以下异常： 无法确定'EF_Associations.Vehicle_Manufacturer'关系的主要结束。多个添加的实体可能具有相同的主键。

堆栈追踪：

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:

我如何指定这种关系的原则结束？

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

您的制造商级别必须只有一个外键属性：Vehicles。

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

您必须修改种子方法才能使用此单个FK属性。 EF将创建一个从实体类的继承链推断出的每层次表模型：

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会生成一个额外的 Discriminator 列，其值来自 Car ， Truck ） >车辆表。

为方便起见，您可以在Manufacturer上创建另外两个（非FK）属性，每个属性包含一个特定于继承的OfType查询：

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();
    }
}

Answer 2

我使用SQL Server 2012和＆＃39;迁移＆＃39;进行了测试。（http://msdn.microsoft.com/en-us/data/jj591621.aspx）

按如下方式对类进行建模：

[Table("Manufacturer")]
public class Manufacturer
{
   public Funcionario()
   {
     Cars = new List<Car>();
     Trucks = new List<Truck>();
   }

    [Key]
    [Required]
    [Column("Id", TypeName = "INT")]
    public int Id { get; set; }

    [Column("Name", TypeName = "VARCHAR")]
    public string Name { get; set; }

    public virtual ICollection<Car> Cars  { get; set; }
    public virtual ICollection<Truck> Trucks { get; set; }
 }

 [Table("Vehicle")]
 public class Vehicle
 {
   [Key]
   [Required]
   [Column("Id", TypeName = "INT")]
   public int Id { get; set; }

   [Column("Colour", TypeName = "VARCHAR")]
   public string Colour { get; set; }

   [Column("ManufacturerId", TypeName = "INT")]
   public int ManufacturerId { get; set; }

   [ForeignKey("ManufacturerId")]
   public virtual Manufacturer Manufacturer { get; set; }
  }

 [Table("Car")]
 public class Car : Vehicle
 { }

 [Table("Truck")]
 public class Truck : Vehicle
 { }

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

 }

无法确定关系的主要结束 - 多个添加的实体可能具有相同的主键

2 个答案: