mybatis多表查询

一对一查询

一对一查询的模型

用户表和订单表的关系为，一个用户有多个订单，一个订单只从属于一个用户

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

一对一查询的语句

对应的sql语句：

SELECT *,o.id oid FROM orders o,USER u WHERE o.uid=u.id;

查询的结果如下：

创建Order和User实体

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;}

创建OrderMapper接口

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

配置OrderMapper.xml

<mapper namespace="com.zjq.mapper.OrderMapper">    <resultMap id="orderMap" type="com.zjq.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 *,o.id oid 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.zjq.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.zjq.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>

测试结果

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

输出：

一对多查询

一对多查询的模型

用户表和订单表的关系为，一个用户有多个订单，一个订单只从属于一个用户

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

一对多查询的语句

对应的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：

修改User实体

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;}

创建UserMapper接口

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

配置UserMapper.xml

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

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("----------------------------------");}

输出：

15:00:24,330 DEBUG findAll:159 - ==>  Preparing: select u.id uid,u.username ,o.id oid,o.ordertime,o.total from user u left join orders o on u.id=o.uid 15:00:24,360 DEBUG findAll:159 - ==> Parameters: 15:00:24,393 DEBUG findAll:159 - <==      Total: 5User{id=1, username='admin', password='null', birthday=null, roleList=null, orderList=[Order{id=1, ordertime=Sun Apr 16 14:23:50 CST 2023, total=2000.0, user=null}]}User{id=2, username='共饮一杯无666', password='null', birthday=null, roleList=null, orderList=[Order{id=2, ordertime=Sun Apr 16 14:23:50 CST 2023, total=8888.0, user=null}]}User{id=3, username='共饮一杯无', password='null', birthday=null, roleList=null, orderList=[Order{id=3, ordertime=Sun Apr 16 14:23:50 CST 2023, total=3699.0, user=null}]}User{id=4, username='共饮一杯无', password='null', birthday=null, roleList=null, orderList=[]}User{id=5, username='共饮一杯无', password='null', birthday=null, roleList=null, orderList=[]}

多对多查询

多对多查询的模型

用户表和角色表的关系为，一个用户有多个角色，一个角色被多个用户使用

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

多对多查询的语句

对应的sql语句：

select u.*,r.*,r.id rid from user u left join sys_user_role ur on u.id=ur.useridinner join sys_role r on ur.roleid=r.id;

查询的结果如下：

创建Role实体，修改User实体

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;}

添加UserMapper接口方法

List<User> findAllUserAndRole();

配置UserMapper.xml

<resultMap id="userRoleMap" type="com.zjq.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.zjq.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 sys_user_role ur on u.id=ur.userid    inner join sys_role r on ur.roleid=r.id;select>

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("----------------------------------");}

11:45:51,443 DEBUG findUserAndRoleAll:159 - ==>  Preparing: SELECT * FROM USER u,sys_user_role ur,sys_role r WHERE u.id=ur.userId AND ur.roleId=r.id 11:45:51,572 DEBUG findUserAndRoleAll:159 - ==> Parameters: User{id=1, username='zjq', password='abc', birthday=Wed Jul 28 00:00:00 GMT+08:00 2021, roleList=[Role{id=1, roleName='CTO', roleDesc='CTO'}, Role{id=2, roleName='COO', roleDesc='COO'}]}User{id=2, username='jack', password='123456', birthday=Fri Aug 20 00:00:00 GMT+08:00 2021, roleList=[Role{id=1, roleName='CTO', roleDesc='CTO'}, Role{id=2, roleName='COO', roleDesc='COO'}]}11:45:51,610 DEBUG findUserAndRoleAll:159 - <==      Total: 411:45:51,618 DEBUG JdbcTransaction:123 - Resetting autocommit to true on JDBC Connection [com.Mysql.jdbc.JDBC4Connection@6ec8211c]11:45:51,619 DEBUG JdbcTransaction:91 - Closing JDBC Connection [com.mysql.jdbc.JDBC4Connection@6ec8211c]11:45:51,619 DEBUG PooledDataSource:363 - Returned connection 1858609436 to pool.

Mybatis的注解开发

MyBatis的常用注解

这几年来注解开发越来越流行，Mybatis也可以使用注解开发方式，这样我们就可以减少编写Mapper

映射文件了。我们先围绕一些基本的CRUD来学习，再学习复杂映射多表操作。

• @Insert：实现新增

• @Update：实现更新

• @Delete：实现删除

• @Select：实现查询

• @Result：实现结果集封装

• @Results：可以与@Result 一起使用，封装多个结果集

• @One：实现一对一结果集封装

• @Many：实现一对多结果集封装

MyBatis的增删改查

我们完成简单的user表的增删改查的操作

private UserMapper userMapper;@Beforepublic void before() throws IOException {    InputStream resourceAsStream = Resources.getResourceAsStream("SqlMapConfig.xml");    SqlSessionFactory sqlSessionFactory = new                  SqlSessionFactoryBuilder().build(resourceAsStream);    SqlSession sqlSession = sqlSessionFactory.openSession(true);    userMapper = sqlSession.getMapper(UserMapper.class);}@Testpublic void testAdd() {    User user = new User();    user.setUsername("测试数据");    user.setPassword("123");    user.setBirthday(new Date());    userMapper.add(user);}@Testpublic void testUpdate() throws IOException {    User user = new User();    user.setId(16);    user.setUsername("测试数据修改");    user.setPassword("abc");    user.setBirthday(new Date());    userMapper.update(user);}@Testpublic void testDelete() throws IOException {    userMapper.delete(16);}@Testpublic void testFindById() throws IOException {    User user = userMapper.findById(1);    System.out.println(user);}@Testpublic void testFindAll() throws IOException {    List<User> all = userMapper.findAll();    for(User user : all){        System.out.println(user);    }}

修改MyBatis的核心配置文件，我们使用了注解替代的映射文件，所以我们只需要加载使用了注解的Mapper接口即可

<mappers>        <mapper class="com.zjq.mapper.UserMapper">mapper>mappers>

或者指定扫描包含映射关系的接口所在的包也可以

<mappers>        <package name="com.zjq.mapper">package>mappers>

MyBatis的注解实现复杂映射开发

实现复杂关系映射之前我们可以在映射文件中通过配置来实现，使用注解开发后，我们可以使用@Results注解，@Result注解，@One注解，@Many注解组合完成复杂关系的配置

一对一查询

一对一查询的模型

用户表和订单表的关系为，一个用户有多个订单，一个订单只从属于一个用户

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

一对一查询的语句

对应的sql语句：

select * from orders;select * from user where id=查询出订单的uid;

创建Order和User实体

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;}

创建OrderMapper接口

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

使用注解配置Mapper

public interface OrderMapper {    @Select("select * from orders")    @Results({            @Result(id=true,property = "id",column = "id"),            @Result(property = "ordertime",column = "ordertime"),            @Result(property = "total",column = "total"),            @Result(property = "user",column = "uid",                    javaType = User.class,                    one = @One(select = "com.zjq.mapper.UserMapper.findById"))    })    List<Order> findAll();}

public interface UserMapper {    @Select("select * from user where id=#{id}")    User findById(int id);    }

测试结果

@Testpublic void testSelectOrderAndUser() {    List<Order> all = orderMapper.findAll();    for(Order order : all){        System.out.println(order);    }}

一对多查询

一对多查询的模型

用户表和订单表的关系为，一个用户有多个订单，一个订单只从属于一个用户

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

一对多查询的语句

对应的sql语句：

select * from user;select * from orders where uid=查询出用户的id;

修改User实体

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;}

创建UserMapper接口

List<User> findAllUserAndOrder();

使用注解配置Mapper

public interface UserMapper {    @Select("select * from user")    @Results({            @Result(id = true,property = "id",column = "id"),            @Result(property = "username",column = "username"),            @Result(property = "password",column = "password"),            @Result(property = "birthday",column = "birthday"),            @Result(property = "orderList",column = "id",                    javaType = List.class,                    many = @Many(select = "com.zjq.mapper.OrderMapper.findByUid"))    })    List<User> findAllUserAndOrder();}public interface OrderMapper {    @Select("select * from orders where uid=#{uid}")    List<Order> findByUid(int uid);}

测试结果

List<User> all = userMapper.findAllUserAndOrder();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("-----------------------------");}

多对多查询

多对多查询的模型

用户表和角色表的关系为，一个用户有多个角色，一个角色被多个用户使用

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

多对多查询的语句

对应的sql语句：

select * from user;select * from role r,user_role ur where r.id=ur.role_id and ur.user_id=用户的id

创建Role实体，修改User实体

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;}

添加UserMapper接口方法

List<User> findAllUserAndRole();

使用注解配置Mapper

public interface UserMapper {    @Select("select * from user")    @Results({        @Result(id = true,property = "id",column = "id"),        @Result(property = "username",column = "username"),        @Result(property = "password",column = "password"),        @Result(property = "birthday",column = "birthday"),        @Result(property = "roleList",column = "id",                javaType = List.class,                many = @Many(select = "com.zjq.mapper.RoleMapper.findByUid"))})List<User> findAllUserAndRole();}public interface RoleMapper {    @Select("select * from role r,user_role ur where r.id=ur.role_id and ur.user_id=#{uid}")    List<Role> findByUid(int uid);}

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("----------------------------------");}

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来源地址：https://blog.csdn.net/qq_35427589/article/details/130464966