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我有 3 个类继承自OwnableSpaceObject，它们通过 ICollections 向其子级提供 2 个导航属性。

从OwnableSpaceObject我希望能够拥有一个像AddChild这样的类，它将一个子类添加到 ICollection 并将其保存到数据库中。

这是OwnableSpaceObject基类：

public abstract class OwnableSpaceObject : SpaceObject
{
    public int? UserId { get; set; }
    public int? ResourcesId { get; set; }

    [ForeignKey("UserId")]
    public virtual UserProfile User { get; set; }

    [ForeignKey("ResourcesId")]
    public virtual Resources Resources { get; set; }

    public virtual ICollection<Structure> Structures { get; set; }
    public virtual ICollection<Ship> Ships { get; set; }
}

这是我尝试使用的方法：

public Structure CheckOrAddChild(StructureType _structureType)
{
    using (ChronosContext db = new ChronosContext())
    {
        var structure = Structures != null ? Structures.FirstOrDefault(x =>   x.StructureTypeId == _structureType.Id) : null;
        if (structure == null)
        {
             Structure newStructure = new Structure(_structureType.Id);
             Structures.Add(newStructure); //this should add the Ship to the database and link it to the parent OwnableSpaceObject right? It errors out right here saying that Structures is null
             db.SaveChanges();

             structure = newStructure;
         }
         return structure;
    }
 }

类似地，一个重载的 CheckOrAddChild 用于添加 Ships：

public virtual Ship CheckOrAddChild(ShipType _shipType)
        {
            using (ChronosContext db = new ChronosContext())
            {
                var ship = Ships != null ? Ships.FirstOrDefault(x => x.ShipTypeId == _shipType.Id) : null;
                if (ship == null)
                {
                    Ship newShip = new Ship(_shipType.Id);
                    Ships.Add(newShip); //this should add the Ship to the database and link it to the parent OwnableSpaceObject right? It errors out right here saying that Ships is null
                    db.SaveChanges();

                    ship = newShip;
                }
                return ship;
            }
        }

这里基本上是 Ships 和 Structures 类的样子：

public class Ship
    {
        public int Id { get; set; }
        public int CurrentAmount { get; set; }
        public int BuildingAmount { get; set; }

        public int ShipTypeId { get; set; }

        [ForeignKey("ShipTypeId")]
        public virtual ShipType ShipType { get; set; }
}

Ship/Structure 类没有 OwnableSpaceObject 的导航属性，因为它会为我所有的 Fleets/Asteroids/Planets 创建一个巨大的表，因为它们都继承自 OwnableSpaceObject。我想将舰队/小行星/行星在表格中分开，但仍然能够将船舶和结构附加到它们。目前，EF 在 Ships/Structures 表中创建了 3 个列，分别命名为“Asteroid_Id”、“Planet_Id”和“Fleet_Id”。我应该为每一个创建一个导航属性并自己手动链接它们吗？我试图避免这种情况以避免重复代码。

有人对此有任何想法吗？这两天我一直在研究，我快要精神崩溃了！

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