Question

尝试进行多对多关联。

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; }
    }
}

这是我的映射：

<?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>

创建模式会生成以下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>，我不想要许多Foo到多个的多对多关系成对的string和Persistent类，其中每对Foo都是唯一的。所有三个值都应创建唯一值。

我该怎么做？

（注意：我包含了Hibernate标签，因为无论是Hibernate还是NHibernate，这种关系的xml映射应该是相同的）

Answer 1

虽然它创建了一个不必要的连接，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。

基本上是：

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>

Answer 2

假设您有一个名为Product {productid，name）的表，以及一个名为Bundle {bundleid，name}的表。现在Product和bundle可以有多对多的映射。因此，创建一个名为BundleProduct {BundleId，ProductId}的新表。现在Nhibernate映射如下所示 -

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();
}

如何在NHibernate中映射多对多的三元关系？

2 个答案: