Having entered the world of NHibernate less than one year ago, I m still developing my "personal" best practice and architectural solutions in this area... now I m facing a pretty simple issue on which I d like to have opinions or suggestions by somebody with more expertise.

情景如下：直接父子关系存储在父节点侧的ISet中。

课程：

public class IDPersisted<IdentifierType>
{
    private IdentifierType _id;

    public IDPersisted()
    {
        _id = default(IdentifierType);
    }

    public IDPersisted(IdentifierType id)
    {
        _id = id;
    }
}

public class SportCenter : IDPersisted<Guid>
{
    ...

    private ISet<Field> _fields = new HashedSet<Field>();

    public bool AddField(Field field)
    {
         field.SportCenter = this;
         return _fields.Add(field);
    }

    public bool RemoveField(Field field)
    {
         field.SportCenter = null;
         return _fields.Remove(field);
    }

    ...
}

public class Field : IDPersisted<Guid>
{
    public Field(String name)
    {
        Name = name;
    }

    public String Name { get; set; }

    public SportCenter SportCenter { get; set; }

    ...
}

正如您所看到的，我有一个实现泛型标识符、相等/哈希值和==/！=操作符的基类，所有这些都依赖于ID字段，在类实例生命周期中被认为是不可变的。SportCenter（父级）和Filed（子级）类都使用Guid标识符进行持久化。SportCenter保存一个集合（实际上是一个Set）的Field实例，在Add / RemoveField方法中管理双向关系。

映射：

<class name="SportCenter" table="SportCenters" lazy="false">
   <id name="ID" column="SportCenterID" >
      <generator class="guid.comb" />
   </id>
    ...
   <set name="Fields" table="Fields" inverse="true" lazy ="true" cascade="all-delete-orphan" access="field.camelcase-underscore">
      <key column="SportCenterID" />
      <one-to-many class="Field" />
   </set>
</class>

<class name="Field" table="Fields" lazy="false">
   <id name="ID" column="FieldID" type="Guid">
      <generator class="guid.comb" />
   </id>
   <property name="Name" column="Name" type="String" not-null="true" />
    ...
   <many-to-one name="SportCenter" column="SportCenterID" class ="SportCenter" not-null="true" lazy="proxy" />
</class>

我已采纳你为测绘这种关系而获得的所有基本建议:反向=“真实”,《一套规则》不能直接获得(进入“现场”)、提单和不发薪。

在我的BLL中，我有一个方法来在特定的运动中心内创建一个新的领域：

public void CreateField(FieldDTO fieldDTO, Guid sportcenterID)
{
   // Retrieve the SportCenter
   SportCenter sportcenter = SportCentersDAO.GetByID(sportcenterID);

   // Prepare the new Field object
   Field field = new Field(fieldDTO.Name);
   ...

   // Add the new field to the SportCenter
   sportcenter.AddField(field);

   // Save the SportCenter
   SportCentersDAO.Save(sportcenter);
}

发生的情况是，当我创建新的Field实例时，它的ID被设置为（即全零），然后我调用AddField，该字段将使用该ID添加到Set中...然后仅在调用时，真正的Guid被分配给field.ID。

This breaks one of the rules you can find in every spec/doc/book about NHibernate that is: never change the ID of an instance while it is stored in an ISet (since the ID is the property by which instances are compared by Equals() as I wrote uphere).

在将字段添加到Set之前，为其提供一个GUID值的ID将带我进入邪恶的“分配”ID，并且如果您回答说不要依赖于ID进行Equals/GetHashCode并找到自然的与模型相关的关键字...好吧，我不相信我曾经在这些属性中找到过提供不可变性/唯一性所应具备的“键”。