Mybatis的多表查询1

特例：
	如果拿出每一个订单，他都只能属于一个用户。
	所以Mybatis就把多对一看成了一对一。

//user表实体类
        private Integer id;
        private String username;
        private String address;
        private String sex;
        private Date birthday;

//account表实体类
       private Integer id;
       private Integer uid;
       private Double money;

       //从表实体应该包含主表实体对象的引用 ：一对一
        private User user;

public interface IAccountDao {
    /**
     * 查询所有账户并查询账户所属的用户 一对一
     * @return
     */
    List<Account> findAll();
}

5、实现配置：
  当我们查询用户时，可以同时得到用户下所包含的账户信息

<mapper namespace="com.rpf.dao.IUserDao">
    <!--定义User的ResuleMap-->
    <resultMap id="userAccountMap" type="user">
        <id property="id" column="id"></id>
        <result property="username" column="username"></result>
        <result property="address" column="address"></result>
        <result property="sex" column="sex"></result>
        <result property="birthday" column="birthday"></result>
    </resultMap>
    <!--配置查询所有-->
    <select id="findAll" resultMap="userAccountMap"><!--resultType="com.rpf.domain.User"-->
        select * from user u left outer join account a on u.id=a.uid
    </select>

</mapper>

   当我们查询账户时，可以同时得到账户的所属用户信息 一对一 一个账户只能有一个用户

<mapper namespace="com.rpf.dao.IAccountDao">
    <!--定义封装account和user的resultMap-->
 <resultMap id="accountUserMap" type="account">
     <id property="id" column="aid"></id>
     <result property="uid" column="uid"></result>
     <result property="money" column="money"></result>
<!--一对一的关系映射配置封装User内容-->
     <association property="user" column="uid" javaType="com.rpf.domain.User">
         <id property="id" column="uid"></id>
         <result property="username" column="username"></result>
         <result property="address" column="address"></result>
         <result property="sex" column="sex"></result>
         <result property="birthday" column="birthday"></result>
     </association>
 </resultMap>
    <!--配置查询所有-->
    <select id="findAll" resultMap="accountUserMap"><!--resultType="com.rpf.domain.User"-->
        select u.*,a.id as aid,a.uid,a.money from account a,user u where u.id=a.uid;
    </select>
</mapper>

 public void testFindAll(){
        List<Account> accounts=accountDao.findAll();
          for (Account account:accounts){
           System.out.println(account);
           System.out.println(account.getUser());
       }
    }

//user表实体类
        private Integer id;
        private String username;
        private String address;
        private String sex;
        private Date birthday;
        //一对多主表实体应该包含从表实体的集合引用
        private List<Account> accounts;

//account表实体类
       private Integer id;
       private Integer uid;
       private Double money;

<mapper namespace="com.rpf.dao.IUserDao">
    <!--定义User的ResuleMap-->
    <resultMap id="userAccountMap" type="user">
        <id property="id" column="id"></id>
        <result property="username" column="username"></result>
        <result property="address" column="address"></result>
        <result property="sex" column="sex"></result>
        <result property="birthday" column="birthday"></result>
          <!--配置User对象中Account集合的映射-->
          <!--collection 一对多的配置标签   ofType是属性的类型-->
        <collection property="accounts" ofType="Account">
            <id  column="aid" property="id"></id>
             <result column="uid" property="uid"></result>
             <result column="money" property="money"></result>
        </collection>
    </resultMap>
    <!--配置查询所有-->
    <select id="findAll" resultMap="userAccountMap"><!--resultType="com.rpf.domain.User"-->
        select * from user u left outer join account a on u.id=a.uid
    </select>

</mapper>

<mapper namespace="com.rpf.dao.IAccountDao">
    <!--定义封装account和user的resultMap-->
 <resultMap id="accountUserMap" type="account">
     <id property="id" column="aid"></id>
     <result property="uid" column="uid"></result>
     <result property="money" column="money"></result>
 </resultMap>
    <!--配置查询所有-->
    <select id="findAll" resultMap="accountUserMap"><!--resultType="com.rpf.domain.User"-->
        select u.*,a.id as aid,a.uid,a.money from account a,user u where u.id=a.uid;
    </select>
</mapper>

 public void findAll(){
        List<User> users=userDao.findAll();
        for (User user:users){
            System.out.println(user);
            System.out.println(user.getAccounts());
        }
    }