如何配置 nHibernate 进行多对多映射？

Question

使用 nHibernate 3.2、C# 4.0、SQL Server 2008 R2 Express

我有两个业务实体 - Broker 和 Market。它们分别存储在brokers和markets表中。我还有 brokerMarkets 表，其中有一个名为 MinIncrement 的额外列。 Broker 和 Market 之间存在多对多关系，但仅当我想要存储 MinIncrement 值时（即它是可选的）。我的类如下所示：

public class Market : BusinessBase
{
    public Market() {}

    public virtual int Id { get; set; }
    public virtual string Symbol { get; set; }
    public virtual string Description { get; set; }
}

public class Broker : BusinessBase
{
    public virtual int Id { get; set; }
    public virtual string Name { get; set; }
    public virtual bool IsDefault { get; set; }
    public virtual bool IsActive { get; set; }
    public virtual ISet<Account> Accounts { get; set; }
}

public class BrokerMarket : Market
{
    public BrokerMarket() { }

    public virtual Broker Broker {get; set;}
    public virtual decimal MinIncrement { get; set; }
}

我的映射文件如下所示： Market.hbm.xml

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
                   assembly="MooDB"
                   namespace="MooDB.BusinessLayer">

    <class name="MooDB.BusinessLayer.Market,MooDB" table="markets">
        <id name="Id" column="marketId" type="Int32" unsaved-value="0">
            <generator class="native" />
        </id>           
        <version name="Version" column="version" type="integer" unsaved-value="0" />
        <property name="Symbol" column="symbol" type="String" length="10" not-null="true" />
        <property name="Description" column="description" type="String" length="30" not-null="true" />

        <set name="Brokers" generic="true" table="brokerMarkets">
            <key column="marketId" />
            <many-to-many column="brokerId" class="MooDB.BusinessLayer.Broker,MooDB" />            
        </set>
    </class>
</hibernate-mapping>

Broker.hbm.xml

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
                   assembly="MooDB"
                   namespace="MooDB.BusinessLayer">

    <class name="MooDB.BusinessLayer.Broker,MooDB" table="brokers">
        <id name="Id" column="brokerId" type="Int32" unsaved-value="0">
            <generator class="native" />
        </id>
        <version name="Version" column="version" type="integer" unsaved-value="0" />
        <property name="Name" column="broker" type="String" length="50" not-null="true" />
        <property name="IsActive" column="isActive" type="bool" not-null="true" />
        <property name="IsDefault" column="isDefault" type="bool" not-null="true" />

        <set name="Markets" generic="true" table="brokerMarkets">
            <key column="brokerId" />
            <many-to-many column="marketId" class="MooDB.BusinessLayer.Market,MooDB" />
        </set>

        <set name="Accounts" table="accounts" generic="true" inverse="true">
            <key column="brokerId" />
            <one-to-many class="MooDB.BusinessLayer.Account,MooDB" />
        </set>
    </class>    
</hibernate-mapping>

在我的数据访问层中，我有一个添加 BrokerMarket 的方法：

public void AddBrokerMarket(BrokerMarket bm)
{
    using (ITransaction tx = _session.BeginTransaction())
    {
        try
        {
            _session.Save(bm);
            _session.Flush();
            tx.Commit();
        }
        catch (HibernateException)
        {
            tx.Rollback();
            throw;
        }
    }
}

在我的单元测试中，我尝试添加一个 BrokerMarket，如下所示：

[Test]
public void CanAddBrokerMarket()
{
    Broker broker = _provider.GetBrokerById(1);
    Market market = _provider.GetMarketById(2);
    var brokerMarket = new BrokerMarket { Broker = broker, Description = market.Description, Symbol = market.Symbol, MinIncrement = 0.01M };
    _provider.AddBrokerMarket(brokerMarket);
}

当我运行测试时，我收到此错误：

运行测试。测试 “MooDBTests/MooDB/Tests/DataLayerTests/CanAddBrokerMarket”失败： 消息 NHibernate.MappingException：没有持久化： MooDB.BusinessLayer.BrokerMarket 堆栈跟踪位于 NHibernate.Impl.SessionFactoryImpl.GetEntityPersister（字符串 实体名称）在NHibernate.Impl.SessionImpl.GetEntityPersister（字符串 实体名称，对象 obj) at NHibernate.Event.Default.AbstractSaveEventListener.SaveWithGenerateId(对象 实体、字符串实体名称、对象任何内容、IEventSource 源、 布尔值 requireImmediateIdAccess) at NHibernate.Event.Default.DefaultSaveOrUpdateEventListener.SaveWithGenerateOrRequestedId(SaveOrUpdateEvent 事件）在 NHibernate.Event.Default.DefaultSaveEventListener.SaveWithGeneeratedOrRequestedId(SaveOrUpdateEvent 事件）在 NHibernate.Event.Default.DefaultSaveOrUpdateEventListener.EntityIsTransient(SaveOrUpdateEvent 事件）在 NHibernate.Event.Default.DefaultSaveEventListener.PerformSaveOrUpdate(SaveOrUpdateEvent 事件）在 NHibernate.Event.Default.DefaultSaveOrUpdateEventListener.OnSaveOrUpdate(SaveOrUpdateEvent 事件）在NHibernate.Impl.SessionImpl.FireSave（SaveOrUpdateEvent 事件）在 NHibernate.Impl.SessionImpl.Save(Object obj) NHibernateDataProvider.cs(91,0)：位于 MooDB.DataLayer.NHibernateDataProvider.AddBrokerMarket(BrokerMarket bm) DataLayerTests.cs(81,0): 在 MooDB.Tests.DataLayerTests.CanAddBrokerMarket()

我不确定我做错了什么。我是否需要在 Market 类中添加 Broker 集合，并在 Broker 类中添加 Market 集合？我确实尝试过，但遇到了同样的错误，而且我认为我在概念上遗漏了一些东西。

更新

我已实施以下更改： Market.hbm.xml

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
                   assembly="MooDB"
                   namespace="MooDB.BusinessLayer">

    <class name="MooDB.BusinessLayer.Market,MooDB" table="markets">
        <id name="Id" column="marketId" type="Int32" unsaved-value="0">
            <generator class="native" />
        </id>           
        <version name="Version" column="version" type="integer" unsaved-value="0" />
        <property name="Symbol" column="symbol" type="String" length="10" not-null="true" />
        <property name="Description" column="description" type="String" length="30" not-null="true" />
      <map name="BrokerMarkets" table="brokerMarkets" lazy="true" cascade="none">
        <cache usage="read-write"/>
        <key column="marketId" />
        <index column="brokerId" type="Int32" />
        <composite-element class="MooDB.BusinessLayer.BrokerMarket,MooDB">
          <parent name="Market"/>
          <property name="MinIncrement" column="minIncrement" type="decimal" />
          <many-to-one name="Broker" class="MooDB.BusinessLayer.Broker,MooDB" column="brokerId" />
        </composite-element>        
      </map>
    </class>
</hibernate-mapping>

Broker.hbm.xml

<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.2"
                   assembly="MooDB"
                   namespace="MooDB.BusinessLayer">

    <class name="MooDB.BusinessLayer.Broker,MooDB" table="brokers">
        <id name="Id" column="brokerId" type="Int32" unsaved-value="0">
            <generator class="native" />
        </id>
        <version name="Version" column="version" type="integer" unsaved-value="0" />
        <property name="Name" column="broker" type="String" length="50" not-null="true" />
        <property name="IsActive" column="isActive" type="bool" not-null="true" />
        <property name="IsDefault" column="isDefault" type="bool" not-null="true" />

        <set name="Accounts" table="accounts" generic="true" inverse="true">
            <key column="brokerId" />
            <one-to-many class="MooDB.BusinessLayer.Account,MooDB" />
        </set>
    </class>    
</hibernate-mapping>

Market 类：

public class Market : BusinessBase
{
    public Market() {}

    public virtual int Id { get; set; }
    public virtual string Symbol { get; set; }
    public virtual string Description { get; set; }
    public virtual ISet<BrokerMarket> BrokerMarkets { get; set; } //added this line
}

BrokerMarket 类

public class BrokerMarket : Market
{
    public BrokerMarket() { }

    public virtual Broker Broker {get; set;}
    public virtual Market Market { get; set; } // added this line
    public virtual decimal MinIncrement { get; set; }
}

其他一切均未更改。我再次运行单元测试，得到：

运行测试。测试 “MooDBTests/MooDB/Tests/DataLayerTests/CanAddBrokerMarket”失败： 消息 TestFixtureSetUp 在 DataLayerTests 中失败

测试“MooDBTests/MooDB/Tests/DataLayerTests”失败：消息设置： NHibernate.MappingException：映射中的重复列 集合：MooDB.BusinessLayer.Market.BrokerMarkets 列：brokerId

UPDATE 2

如果我从市场中删除

。 hbm.xml 运行单元测试时出现此错误：

运行测试。测试 “MooDBTests/MooDB/Tests/DataLayerTests/CanAddBrokerMarket”失败： 消息 TestFixtureSetUp 在 DataLayerTests 中失败

测试“MooDBTests/MooDB/Tests/DataLayerTests”失败：消息设置： NHibernate.MappingException：MooDB.Mappings.Market.hbm.xml(17,10)： XML 验证错误：命名空间中的元素“map” 'urn:nhibernate-mapping-2.2' 具有无效的子元素 命名空间“urn:nhibernate-mapping-2.2”中的“复合元素”。名单 预期可能的元素：'map-key，composite-map-key， 映射键多对多、索引、复合索引、索引多对多、 命名空间“urn:nhibernate-mapping-2.2”中的索引多对任意。 ----> System.Xml.Schema.XmlSchemaValidationException：元素“map” 命名空间“urn：nhibernate-mapping-2.2”具有无效的子元素 命名空间“urn:nhibernate-mapping-2.2”中的“复合元素”。名单 预期可能的元素：'map-key，composite-map-key， 映射键多对多、索引、复合索引、索引多对多、 命名空间“urn:nhibernate-mapping-2.2”中的“索引多对任意”。

Answer 1

该错误可能是因为您尚未定义 BrokerMarket 类的映射，如果您想像您所做的那样保存经纪商市场，则必须创建 BrokerMarket.hbm.xml。您还可以看看在这里使用复合元素，例如 http://thesoftwaresimpleton.blogspot.com/2010/03/nhibernate-many-to-many-with-extra.html