MyBatis从入门到精通(三)—MyBatis多表查询和注解开发

文章目录

• Mybatis多表查询
• • 一对一查询
  • • 一对一查询的模型MapperScannerConfigurer
    • 一对一查询的语句
    • 创建Order和User实体
    • 创建OrderMapper接口
    • 配置OrderMapper.xml
    • 测试结果
  • 一对多查询
  • • 一对多查询的模型
    • 一对多查询的语句
    • 修改User实体
    • 创建UserMapper接口
    • 配置UserMapper.xml
    • 测试结果
  • 多对多查询
  • • 多对多查询的模型
    • 多对多查询的语句
    • 创建Role实体，修改User实体
    • 添加UserMapper接口方法
    • 配置UserMapper.xml
    • 测试结果
• Mybatis的注解开发
• • MyBatis的常用注解
  • MyBatis的增删改查
  • MyBatis的注解实现复杂映射开发
  • 一对一查询
  • • 一对一查询的模型
    • 一对一查询的语句
    • 创建Order和User实体
    • 创建OrderMapper接口
    • 使用注解配置Mapper
    • 测试结果
  • 一对多查询
  • • 一对多查询的模型
    • 一对多查询的语句
    • 修改User实体
    • 创建UserMapper接口
    • 使用注解配置Mapper
    • 测试结果
  • 多对多查询
  • • 多对多查询的模型
    • 多对多查询的语句
    • 创建Role实体，修改User实体
    • 添加UserMapper接口方法
    • 使用注解配置Mapper
    • 测试结果

Mybatis多表查询

一对一查询

一对一查询的模型MapperScannerConfigurer

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：

代码语言：javascript复制

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

查询的结果如下：

创建Order和User实体

代码语言：javascript复制

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

代码语言：javascript复制

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

配置OrderMapper.xml

代码语言：javascript复制

<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 * from orders o,user u where o.uid=u.id
    </select>
</mapper>

其中还可以配置如下：

代码语言：javascript复制

<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

代码语言：javascript复制

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

输出：

代码语言：javascript复制

11:29:37,682 DEBUG JdbcTransaction:137 - Opening JDBC Connection
11:29:38,178 DEBUG PooledDataSource:406 - Created connection 1858609436.
11:29:38,179 DEBUG JdbcTransaction:101 - Setting autocommit to false on JDBC Connection [com.mysql.jdbc.JDBC4Connection@6ec8211c]
11:29:38,182 DEBUG findAll:159 - ==>  Preparing: SELECT *,o.id oid FROM orders o,USER u WHERE o.uid=u.id 
11:29:38,305 DEBUG findAll:159 - ==> Parameters: 
11:29:38,351 DEBUG findAll:159 - <==      Total: 3
11:29:38,357 DEBUG JdbcTransaction:123 - Resetting autocommit to true on JDBC Connection [com.mysql.jdbc.JDBC4Connection@6ec8211c]
Order{id=1, ordertime=Sun Dec 12 00:00:00 GMT 08:00 2021, total=3000.0, user=User{id=1, username='zjq', password='abc', birthday=Wed Jul 28 00:00:00 GMT 08:00 2021, roleList=null}}
Order{id=2, ordertime=Sun Dec 12 00:00:00 GMT 08:00 2021, total=4000.0, user=User{id=1, username='zjq', password='abc', birthday=Wed Jul 28 00:00:00 GMT 08:00 2021, roleList=null}}
Order{id=3, ordertime=Sun Dec 12 00:00:00 GMT 08:00 2021, total=5000.0, user=User{id=2, username='jack', password='123456', birthday=Fri Aug 20 00:00:00 GMT 08:00 2021, roleList=null}}

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：

代码语言：javascript复制

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

代码语言：javascript复制

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

代码语言：javascript复制

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

配置UserMapper.xml

代码语言：javascript复制

<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

代码语言：javascript复制

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：

代码语言：javascript复制

11:38:28,060 DEBUG findAll:159 - ==>  Preparing: SELECT *,o.id oid FROM USER u,orders o WHERE u.id=o.uid 
11:38:28,179 DEBUG findAll:159 - ==> Parameters: 
11:38:28,254 DEBUG findAll:159 - <==      Total: 3
User{id=1, username='zjq', password='abc', birthday=Wed Jul 28 00:00:00 GMT 08:00 2021, roleList=null}
User{id=2, username='jack', password='123456', birthday=Fri Aug 20 00:00:00 GMT 08:00 2021, roleList=null}
11:38:28,265 DEBUG JdbcTransaction:123 - Resetting autocommit to true on JDBC Connection [com.mysql.jdbc.JDBC4Connection@6ec8211c]
11:38:28,265 DEBUG JdbcTransaction:91 - Closing JDBC Connection [com.mysql.jdbc.JDBC4Connection@6ec8211c]
11:38:28,265 DEBUG PooledDataSource:363 - Returned connection 1858609436 to pool.

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：

代码语言：javascript复制

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;

查询的结果如下：

创建Role实体，修改User实体

代码语言：javascript复制

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

代码语言：javascript复制

List<User> findAllUserAndRole();

配置UserMapper.xml

代码语言：javascript复制

<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

代码语言：javascript复制

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

代码语言：javascript复制

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: 4
11:45:51,618 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

代码语言：javascript复制

private UserMapper userMapper;

@Before
public 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);
}

@Test
public void testAdd() {
    User user = new User();
    user.setUsername("测试数据");
    user.setPassword("123");
    user.setBirthday(new Date());
    userMapper.add(user);
}
@Test
public 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);
}

@Test
public void testDelete() throws IOException {
    userMapper.delete(16);
}
@Test
public void testFindById() throws IOException {
    User user = userMapper.findById(1);
    System.out.println(user);
}
@Test
public 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

代码语言：javascript复制

<mappers>
    <!--扫描使用注解的类-->
    <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

代码语言：javascript复制

<mappers>
    <!--扫描使用注解的类所在的包-->
    <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：

代码语言：javascript复制

select * from orders;

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

创建Order和User实体

代码语言：javascript复制

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

代码语言：javascript复制

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

使用注解配置Mapper

代码语言：javascript复制

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();
}

代码语言：javascript复制

public interface UserMapper {

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

测试结果

代码语言：javascript复制

@Test
public 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：

代码语言：javascript复制

select * from user;

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

修改User实体

代码语言：javascript复制

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

代码语言：javascript复制

List<User> findAllUserAndOrder();

使用注解配置Mapper

代码语言：javascript复制

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

代码语言：javascript复制

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：

代码语言：javascript复制

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

代码语言：javascript复制

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

代码语言：javascript复制

List<User> findAllUserAndRole();

使用注解配置Mapper

代码语言：javascript复制

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

代码语言：javascript复制

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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