如何映射NHibernate中的多对多三元关系

本文关键字：三元 关系 何映射 映射 NHibernate | 更新日期: 2023-09-27 18:27:19

尝试建立多对多关联。

到目前为止，我所拥有的是：

namespace com.example // Assembly = com.example
{
    public class Foo
    {
        public virtual long Id { get; set; }
        public virtual IDictionary<string, ISet<PersistentClass>> MappedCollections { get; set; }
    }
    public class PersistentClass
    {
        public virtual long Id { get; protected set; }
        public virtual string Prop { get; set; }
    }
}

这是我的地图：

<?xml version="1.0" encoding="utf-8"?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
  <class name="com.example.Foo, com.example">
    <id name="Id" type="Int64" generator="hilo" />
    <map name="MappedCollections">
      <key column="Id" />
      <index column="Key" type="String" />
      <many-to-many class="com.example.PersistentClass, com.example" />
    </map>
  </class>
  <class name="com.example.PersistentClass, com.example">
    <id name="Id" type="Int64" generator="hilo" />
    <property name="Prop" />
  </class>
</hibernate-mapping>

创建架构会生成以下SQL（SqlServer示例）：

if exists (select 1 from sys.objects where object_id = OBJECT_ID(N'[FKC8D94E45A4783B9]') AND parent_object_id = OBJECT_ID('MappedCollections'))
alter table MappedCollections  drop constraint FKC8D94E45A4783B9

if exists (select 1 from sys.objects where object_id = OBJECT_ID(N'[FKC8D94E46534DBE0]') AND parent_object_id = OBJECT_ID('MappedCollections'))
alter table MappedCollections  drop constraint FKC8D94E46534DBE0

if exists (select * from dbo.sysobjects where id = object_id(N'Foo') and OBJECTPROPERTY(id, N'IsUserTable') = 1) drop table Foo
if exists (select * from dbo.sysobjects where id = object_id(N'MappedCollections') and OBJECTPROPERTY(id, N'IsUserTable') = 1) drop table MappedCollections
if exists (select * from dbo.sysobjects where id = object_id(N'PersistentClass') and OBJECTPROPERTY(id, N'IsUserTable') = 1) drop table PersistentClass
if exists (select * from dbo.sysobjects where id = object_id(N'hibernate_unique_key') and OBJECTPROPERTY(id, N'IsUserTable') = 1) drop table hibernate_unique_key
create table Foo (
    Id BIGINT not null,
   primary key (Id)
)
create table MappedCollections (
    Id BIGINT not null,
   elt BIGINT not null,
   Key NVARCHAR(255) not null,
   primary key (Id, Key) -- !! WRONG !! should be unique (Id, elt, Key)
)
create table PersistentClass (
    Id BIGINT not null,
   Prop NVARCHAR(255) null,
   primary key (Id)
)
alter table MappedCollections 
    add constraint FKC8D94E45A4783B9 
    foreign key (elt) 
    references PersistentClass
alter table MappedCollections 
    add constraint FKC8D94E46534DBE0 
    foreign key (Id) 
    references Foo
create table hibernate_unique_key (
     next_hi BIGINT 
)
insert into hibernate_unique_key values ( 1 )

知道我做错了什么吗？从我们的SQL中，我们可以看到它持久化为IDictionary<string, PersistentClass>而不是IDictionary<string, ISet<PersistentClass>，我不想要string和Persistent类的多对Foo的多对多关系，其中该对对于每个Foo都是唯一的。所有三个值都应创建一个唯一值。

我该怎么做？

（注意：我包含了Hibernate标记，因为无论是Hibernate还是NHibernate，这种关系的xml映射都应该相同）

如何映射NHibernate中的多对多三元关系

尽管它创建了一个不必要的联接，但创建另一个实体可以做到这一点，同时保持一个非常相似的公共接口。

基本上：

namespace com.example // Assembly = com.example
{
    public class Foo
    {
        public virtual long Id { get; set; }
        public virtual ReadOnlyDictionary<string, ISet<PersistentClass>> MappedCollections 
        { 
            get 
            { 
                return new ReadOnlyDictionary<string, ISet<PersistentClass>>(_mc); 
            } 
        }
        protected virtual IDictionary<string, PersistentClassSet> _mc { get; set; }
        public virtual void InitializeCollection(string key)
        {
            if (!_mk.ContainsKey(key))
                _mc[key] = new PersistentClassSet();
        }
    }
    public class PersistentClass
    {
        public virtual long Id { get; protected set; }
        public virtual string Prop { get; set; }
    }
    internal class PersistentClassSet : ISet<PersisitentClass>
    {
        public PersistentClassSet()
        {
            Proxy = new HashSet<PersistentClass>();
        }
        protected virtual long Id { get; set; }
        protected virtual ISet<PersistentClass> Proxy { get; set; }
        public bool Add(PersistentClass item)
        {
            return Proxy.Add(item);
        }
        // other ISet implementations delegated to Proxy 
    }
}

映射如下：

<?xml version="1.0" encoding="utf-8"?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2">
  <class name="com.example.Foo, com.example">
    <id name="Id" type="Int64" generator="hilo" />
    <map name="MappedCollections">
      <key column="Id" />
      <index column="Key" type="String" />
      <many-to-many class="com.example.PersistentClassSet, com.example" />
    </map>
  </class>
  <class name="com.example.PersistentClass, com.example">
    <id name="Id" type="Int64" generator="hilo" />
    <property name="Prop" />
  </class>
  <class name="com.example.PersistentClassSet, com.example">
    <id name="Id" type="Int64" generator="hilo" />
    <set name="Proxy">
      <key column="Id"/>
      <many-to-many class="com.example.PersistentClass, com.example" />
    </set>
  </class>
</hibernate-mapping>

假设您有一个名为Product（productid，name）的表，和一个称为Bundle（bundleid，name）。现在，Product和bundle可以进行多对多映射。因此，创建一个名为BundleProduct｛BundleId，ProductId｝的新表。现在Nhibernate映射如下-

ProductMap
{
  HasManyToMany(x => x.Bundles).Table("BundleProduct").ParentKeyColumn("ProductId").ChildKeyColumn("BundleId").Cascade.None().Inverse().Not.LazyLoad();
}
BundleMap
{
   HasManyToMany(x => x.Products)
                .Table("BundleProduct")
                .ParentKeyColumn("BundleId")
                .ChildKeyColumn("ProductId")
                .Cascade.All();
}
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