Mybatis(三)Mybatis映射开发
4.1 一对一
4.1.1 表对应关系，
4.1.2 实体对应关系
public class Order {
private int id;
private Date ordertime;
private double total;
//代表当前订单属于哪个用户
private User user; }
public class User {
private int id;
private String username;
private String password;
private Date birthday; }
4.1.3 配置 OrderMapper.xml文件
<mapper namespace="com.lagou.mapper.OrderMapper">
<resultMap id="orderMap" type="com.lagou.domain.Order">
<result column="uid" property="user.id"></result>
<result column="username" property="user.username"></result>
<result column="password" property="user.password"></result>
<result column="birthday" property="user.birthday"></result>
</resultMap>
<select id="findAll" resultMap="orderMap">
select * from orders o,user u where o.uid=u.id
</select>
</mapper>
#或者还可以这样配置
<resultMap id="orderMap" type="com.lagou.domain.Order">
<result property="id" column="id"></result>
<result property="ordertime" column="ordertime"></result>
<result property="total" column="total"></result>
<association property="user" javaType="com.lagou.domain.User">
<result column="uid" property="id"></result>
<result column="username" property="username"></result>
<result column="password" property="password"></result>
<result column="birthday" property="birthday"></result>
</association>
</resultMap>
4.2 一对多
4.2.1 表对应关系
查询语句可以写为
select *,o.id oid from user u left join orders o on u.id=o.uid;
4.2.2 实体类关系
public class Order {
private int id;
private Date ordertime;
private double total;
//当前订单属于哪个用户
private User user;
}
public class User {
private int id;
private String username;
private String password;
private Date birthday;
//当前用户的订单列表
private List<Order> orderList;
}
4.2.3 配置UserMapper.xml
<mapper namespace="com.lagou.mapper.UserMapper">
<resultMap id="userMap" type="com.lagou.domain.User">
<result column="id" property="id"></result>
<result column="username" property="username"></result>
<result column="password" property="password"></result>
<result column="birthday" property="birthday"></result>
<collection property="orderList" ofType="com.lagou.domain.Order">
<result column="oid" property="id"></result>
<result column="ordertime" property="ordertime"></result>
<result column="total" property="total"></result>
</collection>
</resultMap>
<select id="findAll" resultMap="userMap">
select *,o.id oid from user u left join orders o on u.id=o.uid
</select>
</mapper>
4.3 多对多
4.3.1 表对应关系
对应SQL语句
select u.,r.,r.id rid from user u left join user_role ur on u.id=ur.user_id
inner join role r on ur.role_id=r.id;
4.3.2 实体类对应关系
public class User {
private int id;
private String username;
private String password;
private Date birthday;
//当前用户具备哪些角色
private List<Role> roleList;
}
public class Role {
private int id;
private String rolename;
}
4.3.3 配置UserMapper.xml文件
<resultMap id="userRoleMap" type="com.lagou.domain.User">
<result column="id" property="id"></result>
<result column="username" property="username"></result>
<result column="password" property="password"></result>
<result column="birthday" property="birthday"></result>
<collection property="roleList" ofType="com.lagou.domain.Role">
<result column="rid" property="id"></result>
<result column="rolename" property="rolename"></result>
</collection>
</resultMap>
<select id="findAllUserAndRole" resultMap="userRoleMap">
select u.*,r.*,r.id rid
from user u
left join user_role ur on u.id=ur.user_id
inner join role r on ur.role_id=r.id
</select>
