nhibernate - 流利的 NHibernate : map list of abstract class with table per concrete class (union-subclass)

Question

我遇到以下情况的问题。

我的类结构如下:

public class Owner
{
    public virtual Guid Id { get; set; }
    public virtual string Name { get; set; }
    public virtual IList<Vehicle> Vehicles { get; set; }
}

public abstract class Vehicle
{
    public virtual long Id { get; set; }
    public virtual string Name { get; set; }
}

public abstract class PoweredVehicle : Vehicle
{
    public virtual string EngineType { get; set; }
}

public class Car : PoweredVehicle
{
    public virtual int Doors { get; set; }
}

public class Truck : PoweredVehicle
{
    public virtual long MaxLoad { get; set; }
}

public class Bicycle : Vehicle
{
    public virtual int FrameSize { get; set; }
}

流畅的映射:

public class OwnerMap : ClassMap<Owner>
{
    public OwnerMap()
    {
        Id(x => x.Id).GeneratedBy.GuidComb();
        Map(x => x.Name);
        HasMany(x => x.Vehicles);
    }
}

public class VehicleMap : ClassMap<Vehicle>
{
    public VehicleMap()
    {
        Id(x => x.Id).GeneratedBy.HiLo("10");
        Map(x => x.Name);
        UseUnionSubclassForInheritanceMapping();
    }
}

public class PoweredVehicleMap : SubclassMap<PoweredVehicle>
{
    public PoweredVehicleMap()
    {
        Map(x => x.EngineType);
        Abstract();
    }
}

public class CarMap : SubclassMap<Car>
{
    public CarMap()
    {
        Map(x => x.Doors);
    }
}

public class TruckMap : SubclassMap<Truck>
{
    public TruckMap()
    {
        Map(x => x.MaxLoad);
    }
}

public class BicycleMap : SubclassMap<Bicycle>
{
    public BicycleMap()
    {
        Map(x => x.FrameSize);
    }
}

我插入一辆汽车和一辆自行车。当我尝试插入带有车辆对象列表的所有者(带有汽车和自行车)时，出现以下错误:

Exception: NHibernate.Exceptions.GenericADOException: could not insert collection: [NHibernateTest.Owner.Vehicles#8ace95bc-ad80-46d7-94c7-a11f012b67c6][SQL: UPDATE "Vehicle" SET Owner_id = @p0 WHERE Id = @p1] ---> System.Data.SQLite.SQLiteException: SQLite error

既然我为每个具体类都设置了表，为什么 NHibernate 会尝试更新一个不存在的代表基类的表？这种场景不支持这种类型的映射吗？

此外，当我从 HasMany 更改为 HasManyToMany 时，效果很好。

Answer 1

在这种情况下，唯一的选择是 Inverse() 映射。这意味着具体的 Vehicle (Car, Bicycle) 必须关心关系的持久性。

要启用此功能，请使用新属性扩展 Vehicle 类:

public abstract class Vehicle
{ 
  ..
  // new owner independent navigation property
  public virtual Guid OwnerId { get; set; } 
}

并扩展 Vehicle 的映射

public VehicleMap()
{  
  ..
  Map(x => x.OwnerId).Column("Owner_id);
}

最后反转持久性责任。不是所有者，但集合项将关心正确的 Owner_id 列更改(当调用具体的 Vehicle 插入/更新时)。

(更多关于逆:https://stackoverflow.com/a/1454445/1679310)

public OwnerMap()
{
  ..
  HasMany(x => x.Vehicles)
    .Inverse()
    .Cascade.All();
}

当 Vehicle 被添加到 Owner 的集合中时，它的 OwnerId 也必须被赋值:

owner.Vehicles.Add(car);
car.OwnerId = owner.Id;