Mybatis复杂映射开发：一对一一对多多对多查询

Posted 2021-05-25 丿涛哥哥

Mybatis复杂映射开发：一对一、一对多、多对多查询

1、 一对一查询

1.1、 一对一查询的模型

一对一查询的需求：查询一个订单，与此同时查询出该订单所属的用户

1.2、一对一查询的语句

sql语句：

select * from orders o,user u where o.uid=u.id;

查询的结果如下：

1.3、 创建Order.java和User.java实体类

public class Order {
    private int id;
    private Date ordertime;
    private double total;
    //代表当前订单从属于哪一个客户
    private User user;
}

public class User {
    private int id;
    private String username;
    private String password;
    private Date birthday;
}

1.4、 创建OrderMapper.java接口

public interface OrderMapper {
	List<Order> findAll();
}

1.5、 配置OrderMapper.xml映射配置文件

<mapper namespace="com.tao.mapper.OrderMapper">
    <resultMap id="orderMap" type="com.tao.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>

其中还可以配置如下：

<resultMap id="orderMap" type="com.tao.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.tao.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>

1.6、 测试结果

OrderMapper mapper = sqlSession.getMapper(OrderMapper.class);
List<Order> all = mapper.findAll();
for(Order order : all){
	System.out.println(order);
}

2、 一对多查询

2.1、 一对多查询的模型

一对多查询的需求：查询一个用户，与此同时查询出该用户具有的订单

2.2、 一对多查询的语句

sql语句：

select *,o.id oid from user u left join orders o on u.id=o.uid;

查询的结果如下：

2.3、 修改User.java实体类

public class Order {
    private int id;
    private Date ordertime;
    private double total;
    //代表当前订单从属于哪一个客户
    private User user;
}

public class User {
    private int id;
    private String username;
    private String password;
    private Date birthday;
    //代表当前用户具备哪些订单
    private List<Order> orderList;
}

2.4、 创建UserMapper.java接口

public interface UserMapper {
	List<User> findAll();
}

2.5、 配置UserMapper.xml映射配置文件

<mapper namespace="com.tao.mapper.UserMapper">
    <resultMap id="userMap" type="com.tao.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.tao.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>

2.6、 测试结果

UserMapper mapper = sqlSession.getMapper(UserMapper.class);
List<User> all = mapper.findAll();
for(User user : all){
    System.out.println(user.getUsername());
    List<Order> orderList = user.getOrderList();
    for(Order order : orderList){
    	System.out.println(order);
    }
    System.out.println("----------------------------------");
}

3、 多对多查询

3.1、 多对多查询的模型

多对多查询的需求：查询用户同时查询出该用户的所有角色

3.2、 多对多查询的语句

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;

查询的结果如下：

3.3、 创建Role.java，修改User.java实体类

public class User {
    private int id;
    private String username;
    private String password;
    private Date birthday;
    //代表当前用户具备哪些订单
    private List<Order> orderList;
    //代表当前用户具备哪些角色
    private List<Role> roleList;
}

public class Role {
    private int id;
    private String rolename;
}

3.4、 添加UserMapper.java接口方法

List<User> findAllUserAndRole();

3.5、 配置UserMapper.xml映射配置文件

<resultMap id="userRoleMap" type="com.tao.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.tao.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>

3.6、 测试结果

UserMapper mapper = sqlSession.getMapper(UserMapper.class);
List<User> all = mapper.findAllUserAndRole();
for(User user : all){
    System.out.println(user.getUsername());
    List<Role> roleList = user.getRoleList();
    for(Role role : roleList){
    	System.out.println(role);
    }
    System.out.println("----------------------------------");
}