NHibernate使用复合主键(一)
引用：http://blog.csdn.net/liangxunjian/archive/2006/08/11/1048625.aspx
主要是关于:<composite-id>元素接受<key-property>
将在使用复合主键(2)中讲到<key-many-to-one>
属性映射我目前在实施一个.net项目中，使用了ORM工具，参考了java的hibernate，选用了.NET的NHibernate，在开发过程中出现数据库中表的复合主键的情况，其实它跟hibernate中使用的复合主键的情况雷同，但参照了相关的帮助文档，还是要费了一些小的工夫，才能解决了问题．为了避免以后再出现重复问题而浪费时间，现在将在NHibernate中复合主键使用做了以下详细的说明．
本人在测试过程中，建立了一个简单的图书馆管理系统应用工程，数据库中主要的表简要设计如下：
Users表(用户信息表)：
UserID char(10) not null primary key,
UserName varchar(50)
Books表（图书信息表）：
BSN char(10) not null primary key,
BookName varchar(50)
BorrowRecord表（图书借还登记表）：
UserID char(10) not null,
BSN char(10) not null,
BorrowDate DateTime not null,
ReturnDate DateTime,
constraint PK_Library primary key (UserID,BSN,BorrowDate)
手工书写的ORM映射文件如下：
======================================================================
User类：
using System;
using System.Collections.Generic;
using System.Text;
namespace NHDataLayer.NHibernate.Entities
{
[Serializable]
public class User
{
public User()
{
}
private string userID;
public virtual string UserID
{
set
{
userID = value;
}
get
{
return userID;
}
}
private string userName;
public virtual string UserName
{
set
{
userName = value;
}
get
{
return userName;
}
}
}
}
User的xml映射文件(User.hbm.xml)：
<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.0">
<class name="NHDataLayer.NHibernate.Entities.User,NHDataLayer" table="Users">
<id name="UserID" type="String" length="10">
<generator class="assigned" />
</id>
<property name="UserName" type="String" length="50"/>
</class>
</hibernate-mapping>
=====================================================================
======================================================================
Books类：
using System;
using System.Collections.Generic;
using System.Text;
namespace NHDataLayer.NHibernate.Entities
{
[Serializable]
public class Books
{
public Books()
{
}
private string bSN;
public virtual string BSN
{
set
{
bSN = value;
}
get
{
return bSN;
}
}
private string bookName;
public virtual string BookName
{
set
{
bookName = value;
}
get
{
return bookName;
}
}
private DateTime publishDate;
public virtual DateTime PublishDate
{
set
{
publishDate = value;
}
get
{
return publishDate;
}
}
private string publisher;
public virtual string Publisher
{
set
{
publisher = value;
}
get
{
return publisher;
}
}
private string authors;
public virtual string Authors
{
set
{
authors = value;
}
get
{
return authors;
}
}
public override bool Equals(object obj)
{
return base.Equals(obj);
}
public override int GetHashCode()
{
return base.GetHashCode();
}
}
}
Books的xml映射文件(Book.hbm.xml)：
<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.0">
<class name="NHDataLayer.NHibernate.Entities.Books,NHDataLayer" table="Books">
<id name="BSN" type="String" length="20">
<generator class="assigned" />
</id>
<property name="BookName" type="String" length="50"/>
<property name="PublishDate" type="DateTime"/>
<property name="Publisher" type="String" length="100"/>
<property name="Authors" type="String" length="50"/>
</class>
</hibernate-mapping>
==================================================================
===================================================================
BorrowRecord类：
using System;
using System.Collections.Generic;
using System.Text;
namespace NHDataLayer.NHibernate.Entities
{
[Serializable]
public class BorrowRecord
{
public BorrowRecord()
{
}
private BorrowRecordPK borrowPK;
public virtual BorrowRecordPK BorrowPK
{
set
{
borrowPK = value;
}
get
{
return borrowPK;
}
}
private int total;
public virtual int Total
{
set
{
total = value;
}
get
{
return total;
}
}
private DateTime returnDate;
public virtual DateTime ReturnDate
{
set
{
returnDate = value;
}
get
{
return returnDate;
}
}
/// <summary>
/// 判断两个对象是否相同，这个方法需要重写
/// </summary>
/// <param name="obj">进行比较的对象</param>
/// <returns>真true或假false</returns>
public override bool Equals(object obj)
{
if (obj is BorrowRecord)
{
BorrowRecord second = obj as BorrowRecord;
if (this.BorrowPK.UserID == second.BorrowPK.UserID
&& this.BorrowPK.BSN == second.BorrowPK.BSN
&& this.BorrowPK.BorrowDate == second.BorrowPK.BorrowDate)
{
return true;
}
else return false;
}
return false;
}
public override int GetHashCode()
{
return base.GetHashCode();
}
}
}
BorrowRecord复合主键类：
using System;
using System.Collections.Generic;
using System.Text;
namespace NHDataLayer.NHibernate.Entities
{
[Serializable]
public class BorrowRecordPK
{
public BorrowRecordPK()
{
}
private string userID;
public virtual string UserID
{
set
{
userID = value;
}
get
{
return userID;
}
}
private string bSN;
public virtual string BSN
{
set
{
bSN = value;
}
get
{
return bSN;
}
}
private DateTime borrowDate;
public virtual DateTime BorrowDate
{
set
{
borrowDate = value;
}
get
{
return borrowDate;
}
}
public override bool Equals(object obj)
{
return base.Equals(obj);
}
public override int GetHashCode()
{
return base.GetHashCode();
}
}
}
BorrowRecord的xml映射文件(BorrowRecord.hbm.xml)：
<?xml version="1.0" encoding="utf-8" ?>
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.0">
<class name="NHDataLayer.NHibernate.Entities.BorrowRecord,NHDataLayer" table="BorrowRecord">
<composite-id name="BorrowPK" class="NHDataLayer.NHibernate.Entities.BorrowRecordPK,NHDataLayer">
<key-property name="UserID"/>
<key-property name="BSN"/>
<key-property name="BorrowDate"/>
</composite-id>
<property name="ReturnDate" type="DateTime"/>
<property name="Total" type="Int16"/>
</class>
</hibernate-mapping>
==============================================================================
主要要注意的是：
1、使用了复合主键类要重写Equals()和GetHashCode()方法。
2、要将该复合类Serializable.
3、xml映射文件要设置为嵌入的资源。
这样，我们就可以使用ISession的Get()或Load()方法，通过键获取实体了。
关于更详细的信息，请参考NHibernate的相关文档。