MyBatis的关联查询之一对多,多对一
在关系型数据库中,我们经常要处理一对多,多对一和多对多的关系。
一对多,多对一
一、entity 实体类
public class SmbmsRole {
private long rid;
private String roleCode;
private String roleName;
//泛型集合
private List<User> users;
public List<User> getUsers() {
return users;
}
public void setUsers(List<User> users) {
this.users = users;
}
public long getRid() {
return rid;
}
public void setRid(long rid) {
this.rid = rid;
}
public String getRoleCode() {
return roleCode;
}
public void setRoleCode(String roleCode) {
this.roleCode = roleCode;
}
public String getRoleName() {
return roleName;
}
public void setRoleName(String roleName) {
this.roleName = roleName;
}
}
public class User {
private Integer uid;
private String userCode;
private String userName;
//关联一的一方
private SmbmsRole role;
public SmbmsRole getRole() {
return role;
}
public void setRole(SmbmsRole role) {
this.role = role;
}
public Integer getUid() {
return uid;
}
public void setUid(Integer uid) {
this.uid = uid;
}
public String getUserCode() {
return userCode;
}
public void setUserCode(String userCode) {
this.userCode = userCode;
}
public String getUserName() {
return userName;
}
public void setUserName(String userName) {
this.userName = userName;
}
二、dao层
//一对多
//根据角色获取所对应的人
SmbmsRole getroleId(Integer rid);
//多对一 查询所有用户信息
List<User> getUserList();
三、小配置 xml
<!--一对多-->
<!--由于是关联查询 返回的是多张表中的结果集,必须定义resultMap映射-->
<resultMap id="SmbmsRoleMaps" type="com.marketsys.entity.SmbmsRole">
<id column="rid" property="rid"></id>
<!--此处使用的是collection节点,由于在SmbmsRole类中插入的是List集合
ofType:为集合中的泛型-->
<collection property="users" ofType="User" select="getroleIdMutilSQL" column="rid">
<!--在collection中声明Provincial中的属性与表中列的映射-->
<!-- <id column="uid" property="uid"></id>-->
</collection>
</resultMap>
<!--一对多 一条select-->
<!--<select id="getroleId" parameterType="int" resultMap="SmbmsRoleMaps">
select r.rid,roleName,u.uid,userName from smbms_role r inner join smbms_user u on r.rid=u.userRole where r.rid=#{rid}
</select>-->
<!--一对多 两条select-->
<select id="getroleId" resultMap="SmbmsRoleMaps">
select * from smbms.smbms_role where rid=#{rid}
</select>
<select id="getroleIdMutilSQL" resultType="com.marketsys.entity.User">
select * from smbms.smbms_user where userRole=#{rid}
</select>
<!--多对一-->
<resultMap id="SmbmsRoleMap" type="com.marketsys.entity.User">
<id column="uid" property="uid"></id>
<association property="role" javaType="com.marketsys.entity.SmbmsRole" select="getRole" column="userRole">
<id column="rid" property="rid"></id>
</association>
</resultMap>
<!-- 多对一 一条select-->
<!--<select id="getUserList" resultMap="SmbmsRoleMap">
select rid,roleName,uid,userName from smbms_role,smbms_user where smbms_role.rid=smbms_user.userRole
</select>-->
<!-- 多对一 二条select-->
<select id="getUserList" resultMap="SmbmsRoleMap">
select uid,userName,userRole from smbms.smbms_user
</select>
<select id="getRole" resultType="com.marketsys.entity.SmbmsRole">
select rid,roleName from smbms.smbms_role where rid=#{userRole}
</select>
四、test测试类
SqlSession sqlSession= MybatisUtil.getSqlSession();
URoleTestDao mapper=sqlSession.getMapper(URoleTestDao.class);
//一对多
@Test
public void test1(){
SmbmsRole smbmsRole=mapper.getroleId(3);
System.out.println("身份为:"+smbmsRole.getRoleName()+"\n姓名为:");
for (User item:smbmsRole.getUsers()) {
System.out.println(item.getUserName());
}
}
//多对一
@Test
public void test2(){
List<User> userList = mapper.getUserList();
for (User user:userList) {
System.out.println("用户:"+user.getUserName()+"\t角色:"+user.getRole().getRoleName());
}
}