Hibernate one-to-many映射要注意的问题及详细例子

使用场合：
table1中主键id被table2作为外键引用，一条table1的记录可能有多条table2记录对应。
在页面上执行删除一条table1的操作， table1的id值传到java程序，删除table1的id=${id}之前必须删除table2关联的记录，因为有外键约束关系，所以必须先删除table2的相关记录，否则报错；而删除table2的记录不需要自己写代码删除， 因为有声明了hibernate one-to-many映射，直接删除table1的记录就行了。
不过要注意的是， 删除table1的记录前， 要先通过id获取table1的记录对象，否则无法删除成功。

举例==>
逻辑： 一个邮件接收用户可以关联多个产品， 如果删除了邮件接收用户， 那么产品关联邮件接收用户表的记录也要删除。

1) 数据库表：

/*==============================================================*/
/* Table: 产品关联邮件接受用户表                                */
/*==============================================================*/
CREATE TABLE IPMS_TYPE_RELA_USER (
   ID                   varchar(64)          not null,
   PROJTYPEID           varchar(64)          null,
   USERID               varchar(64)          null,
   constraint PK_IPMS_TYPE_RELA_USER primary key nonclustered (ID)
)
go


ALTER TABLE IPMS_TYPE_RELA_USER
   ADD CONSTRAINT FK_2 FOREIGN KEY (USERID)
      REFERENCES IPMS_EMAIL_USER (ID)
go

/*==============================================================*/
/* Table: 邮件接受用户表                                        */
/*==============================================================*/
CREATE TABLE IPMS_EMAIL_USER (
   ID                   varchar(64)          not null,
   NAME                 varchar(64)          null,
   ACCOUNTS             varchar(64)          null,
   POSITION             varchar(32)          null,
   EMAIL                varchar(100)         null,
   constraint PK_IPMS_EMAIL_USER primary key nonclustered (ID)
)
go

2) Java代码：
/** TypeRelaUser.java */

public class TypeRelaUser extends BaseData{

    /** id */
	private String id;
    /** 产品对象 */
	private ProjectType projectType;
    /** 邮件接收用户对象 */
	private EmailUser emailUser;


	public void setId(String id) {
		this.id = id;
	}
	
	public String getId() {
		return id;
	}
	
	public void setProjectType(ProjectType projectType) {
		this.projectType = projectType;
	}
	
	public ProjectType getProjectType() {
		return projectType;
	}
	
	public void setEmailUser(EmailUser emailUser) {
		this.emailUser = emailUser;
	}
	
	public EmailUser getEmailUser() {
		return emailUser;
	} 

}

/** TypeRelaUser.hbm.xml */

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC 
	"-//Hibernate/Hibernate Mapping DTD 3.0//EN"
	"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
    
<hibernate-mapping>
<class name="com.toone.ipms.projtype.rela.model.TypeRelaUser" table="IPMS_TYPE_RELA_USER">
    <id name="id" type="java.lang.String" column="ID">
		<generator class="uuid.hex" />
    </id>  
	<many-to-one name="projectType" column="PROJTYPEID" class="com.toone.ipms.projtype.type.model.ProjectType">
	</many-to-one>
	<many-to-one name="emailUser" column="USERID" class="com.toone.ipms.emailuser.model.EmailUser">
	</many-to-one>

</class>

<query name="getAllTypeRelaUsers">
	from TypeRelaUser c 
	order by c.id desc
</query>
<query name="deleteTypeRelaUsersByUserIds">
	delete from TypeRelaUser c 
	where c.emailUser.id in (:userIds) 
</query>
</hibernate-mapping>

/** EmailUser.java */

public class EmailUser extends BaseData{

    /** id */
    private String id;
    /** 用户名 */
    private String name;
    /** 账号 */
    private String accounts;
    /** 职位 */
    private String positionName;
    /** 邮件地址 */
    private String email;
    /** 产品类型关联干系用户集合 */
    private Set typeRelaUserSet = new HashSet();
    /** 项目关联干系用户对象 */
    private Set projRelaUserSet = new HashSet();
    
    public void setTypeRelaUserSet(Set typeRelaUserSet){
        this.typeRelaUserSet = typeRelaUserSet;
    }
    
    public Set getTypeRelaUserSet(){
        return this.typeRelaUserSet;
    }

    public void setProjRelaUserSet(Set projRelaUserSet){
        this.projRelaUserSet = projRelaUserSet;
    }
    
    public Set getProjRelaUserSet(){
        return this.projRelaUserSet;
    }
    
    public void setId(String id) {
        this.id = id;
    }
    
    public String getId() {
        return id;
    }
    
    public void setName(String name) {
        this.name = name;
    }
    
    public String getName() {
        return name;
    }
    
    public void setAccounts(String accounts) {
        this.accounts = accounts;
    }
    
    public String getAccounts() {
        return accounts;
    }
    
    public void setPositionName(String positionName) {
        this.positionName = positionName;
    }
    
    public String getPositionName() {
        return positionName;
    }
    
    public void setEmail(String email) {
        this.email = email;
    }
    
    public String getEmail() {
        return email;
    }
    

}

/** EmailUser.hbm.xml */

<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC 
    "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
    
<hibernate-mapping>
<class name="com.toone.ipms.emailuser.model.EmailUser" table="IPMS_EMAIL_USER">
    <id name="id" type="java.lang.String" column="ID">
        <generator class="uuid.hex" />
    </id>
   <property
        name="name"
        type="java.lang.String"
        column="NAME"
        length="64"
    />
   <property
        name="accounts"
        type="java.lang.String"
        column="ACCOUNTS"
        length="64"
    />
   <property
        name="positionName"
        type="java.lang.String"
        column="POSITIONNAME"
        length="32"
    />
   <property
        name="email"
        type="java.lang.String"
        column="EMAIL"
        length="100"
    />
    <set name="typeRelaUserSet" lazy="false" inverse="true" cascade="delete">
        <key column="USERID" />
        <one-to-many class="com.toone.ipms.projtype.rela.model.TypeRelaUser" />
    </set>
    <set name="projRelaUserSet" lazy="false" inverse="true" cascade="delete">
        <key column="USERID" />
        <one-to-many class="com.toone.ipms.proj.rela.model.ProjectRelaUser" />
    </set>
    
</class>
<query name="getAllEmailUsers">
	from EmailUser c 
	order by c.name, c.accounts
</query>
<query name="checkExistEmailUser">
	from EmailUser c
	where (c.id!=:id or :id is null)
	and (:name is null or c.name=:name)
	and (:accounts is null or c.accounts=:accounts)
	and (:email is null or c.email=:email)
</query> 

</hibernate-mapping>

/** EmailUserService.java */

public class EmailUserService {
	
    protected EmailUserDAO emailUserDAO;


    public void setEmailUserDAO(EmailUserDAO emailUserDAO) {
        this.emailUserDAO = emailUserDAO;
    }

	/**
	 *  删除一个邮件接收人信息对象
	 * @param emailUser EmailUser对象
	 */
	public void deleteEmailUser(EmailUser emailUser) {
		emailUser = emailUserDAO.getEmailUserById(emailUser.getId());
//注意这里，先获取一个emailUser对象，这个对象可能包含会级联删除的产品关联用户表记录对象
//如果不先获取接收邮件用户对象，则删除会失败
		emailUserDAO.deleteEmailUser(emailUser);
	}


}

/** EmailUserDAO.java */

public class EmailUserDAO extends BaseDAO {

    /**
     * 通过id获得邮件接收人信息对象
     * @param id
     * @return
     */
	public EmailUser getEmailUserById( String id) {
    	return (EmailUser)this.load(EmailUser.class, id);
    }

    /**
     *  删除一个邮件接收人信息对象
     * @param emailUser EmailUser对象
     */
    public void deleteEmailUser(EmailUser emailUser) {
    	this.delete(emailUser);
    }

}