MyBatis多表查詢和注解開發(fā)案例詳解
Mybatis多表查詢
一對一查詢
一對一查詢的模型
用戶表和訂單表的關系為,一個用戶有多個訂單,一個訂單只從屬于一個用戶
一對一查詢的需求:查詢一個訂單,與此同時查詢出該訂單所屬的用戶
一對一查詢的語句
對應的sql語句:
SELECT *,o.id oid FROM orders o,USER u WHERE o.uid=u.id;
查詢的結果如下:
創(chuàng)建Order和User實體
public class Order { private int id; private Date ordertime; private double total; //代表當前訂單從屬于哪一個客戶 private User user; } public class User { private int id; private String username; private String password; private Date birthday; }
創(chuàng)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>
其中還可以配置如下:
<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> <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>
測試結果
OrderMapper mapper = sqlSession.getMapper(OrderMapper.class);
List<Order> all = mapper.findAll();
for(Order order : all){
System.out.println(order);
}
輸出:
一對多查詢
一對多查詢的模型
用戶表和訂單表的關系為,一個用戶有多個訂單,一個訂單只從屬于一個用戶
一對多查詢的需求:查詢一個用戶,與此同時查詢出該用戶具有的訂單
一對多查詢的語句
對應的sql語句:
select *,o.id oid from user u left join orders o on u.id=o.uid;
查詢的結果如下:
修改User實體
public class Order { private int id; private Date ordertime; private double total; //代表當前訂單從屬于哪一個客戶 private User user; } public class User { private int id; private String username; private String password; private Date birthday; //代表當前用戶具備哪些訂單 private List<Order> orderList; }
創(chuàng)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>
測試結果
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("----------------------------------");
}
輸出:
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: 5
User{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='共飲一杯無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='共飲一杯無', 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='共飲一杯無', password='null', birthday=null, roleList=null, orderList=[]}
User{id=5, username='共飲一杯無', password='null', birthday=null, roleList=null, orderList=[]}
多對多查詢
多對多查詢的模型
用戶表和角色表的關系為,一個用戶有多個角色,一個角色被多個用戶使用
多對多查詢的需求:查詢用戶同時查詢出該用戶的所有角色
多對多查詢的語句
對應的sql語句:
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;
查詢的結果如下:
創(chuàng)建Role實體,修改User實體
public class User { private int id; private String username; private String password; private Date birthday; //代表當前用戶具備哪些訂單 private List<Order> orderList; //代表當前用戶具備哪些角色 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>
測試結果
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: 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的注解開發(fā)
MyBatis的常用注解
這幾年來注解開發(fā)越來越流行,Mybatis也可以使用注解開發(fā)方式,這樣我們就可以減少編寫Mapper
映射文件了。我們先圍繞一些基本的CRUD來學習,再學習復雜映射多表操作。
@Insert
:實現(xiàn)新增@Update
:實現(xiàn)更新@Delete
:實現(xiàn)刪除@Select
:實現(xiàn)查詢@Result
:實現(xiàn)結果集封裝@Results
:可以與@Result 一起使用,封裝多個結果集@One
:實現(xiàn)一對一結果集封裝@Many
:實現(xiàn)一對多結果集封裝
MyBatis的增刪改查
我們完成簡單的user表的增刪改查的操作
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("測試數(shù)據(jù)"); 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("測試數(shù)據(jù)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,我們使用了注解替代的映射文件,所以我們只需要加載使用了注解的Mapper接口即可
<mappers> <!--掃描使用注解的類--> <mapper class="com.zjq.mapper.UserMapper"></mapper> </mappers>
或者指定掃描包含映射關系的接口所在的包也可以
<mappers> <!--掃描使用注解的類所在的包--> <package name="com.zjq.mapper"></package> </mappers>
MyBatis的注解實現(xiàn)復雜映射開發(fā)
實現(xiàn)復雜關系映射之前我們可以在映射文件中通過配置來實現(xiàn),使用注解開發(fā)后,我們可以使用@Results注解,@Result注解,@One注解,@Many注解組合完成復雜關系的配置
一對一查詢
一對一查詢的模型
用戶表和訂單表的關系為,一個用戶有多個訂單,一個訂單只從屬于一個用戶
一對一查詢的需求:查詢一個訂單,與此同時查詢出該訂單所屬的用戶
一對一查詢的語句
對應的sql語句:
select * from orders; select * from user where id=查詢出訂單的uid;
創(chuàng)建Order和User實體
public class Order { private int id; private Date ordertime; private double total; //代表當前訂單從屬于哪一個客戶 private User user; } public class User { private int id; private String username; private String password; private Date birthday; }
創(chuàng)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); }
測試結果
@Test
public void testSelectOrderAndUser() {
List<Order> all = orderMapper.findAll();
for(Order order : all){
System.out.println(order);
}
}
一對多查詢
一對多查詢的模型
用戶表和訂單表的關系為,一個用戶有多個訂單,一個訂單只從屬于一個用戶
一對多查詢的需求:查詢一個用戶,與此同時查詢出該用戶具有的訂單
一對多查詢的語句
對應的sql語句:
select * from user; select * from orders where uid=查詢出用戶的id;
修改User實體
public class Order { private int id; private Date ordertime; private double total; //代表當前訂單從屬于哪一個客戶 private User user; } public class User { private int id; private String username; private String password; private Date birthday; //代表當前用戶具備哪些訂單 private List<Order> orderList; }
創(chuàng)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); }
測試結果
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("-----------------------------");
}
多對多查詢
多對多查詢的模型
用戶表和角色表的關系為,一個用戶有多個角色,一個角色被多個用戶使用
多對多查詢的需求:查詢用戶同時查詢出該用戶的所有角色
多對多查詢的語句
對應的sql語句:
select * from user; select * from role r,user_role ur where r.id=ur.role_id and ur.user_id=用戶的id
創(chuàng)建Role實體,修改User實體
public class User { private int id; private String username; private String password; private Date birthday; //代表當前用戶具備哪些訂單 private List<Order> orderList; //代表當前用戶具備哪些角色 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); }
測試結果
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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