MyBatis多表操作查询功能 MyBatis多表操作查询功能

一对一查询用户表和订单表的关系为，一个用户多个订单，一个订单只从属一个用户
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

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在只查询order表的时候，也要查询user表，所以需要将所有数据全部查出进行封装SELECT *,o.id oid FROM orders o,USER u WHERE o.uid=u.id

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创建Order和User实体
order

public class Order {private int id; private Date ordertime; private double total; //表示当前订单属于哪一个用户private User user;

user

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

创建OrderMapper接口

public interface UserMapper {//查询全部的方法public List findAll(); }

配置OrderMapper.xml

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

sqlMapConfig.xml

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在一对一配置的时候，在order实体中创建了一个user，所以property属性都使用user.** 的方式进行编写，但是这里还可以使用association

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

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，一个当但只从属一个用户
一对多查询需求：查询一个用户，与此同时查询出该用户具有的订单

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package com.zg.domain; import java.util.Date; import java.util.List; public class User {private int id; private String username; private String password; private Date birthday; //描述当前用户存在哪些订单private ListorderList; public List getOrderList() {return orderList; }public void setOrderList(List orderList) {this.orderList = orderList; }@Overridepublic String toString() {return "User{" +"id=" + id +", username='" + username + '\'' +", password='" + password + '\'' +", birthday=" + birthday +", orderList=" + orderList +'}'; }public int getId() {return id; }public void setId(int id) {this.id = id; }public String getUsername() {return username; }public void setUsername(String username) {this.username = username; }public String getPassword() {return password; }public void setPassword(String password) {this.password = password; }public Date getBirthday() {return birthday; }public void setBirthday(Date birthday) {this.birthday = birthday; }}

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修改User实体

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package com.zg.domain; import java.util.Date; import java.util.List; public class User {private int id; private String username; private String password; private Date birthday; //描述当前用户存在哪些订单private ListorderList; public List getOrderList() {return orderList; }public void setOrderList(List orderList) {this.orderList = orderList; }@Overridepublic String toString() {return "User{" +"id=" + id +", username='" + username + '\'' +", password='" + password + '\'' +", birthday=" + birthday +", orderList=" + orderList +'}'; }public int getId() {return id; }public void setId(int id) {this.id = id; }public String getUsername() {return username; }public void setUsername(String username) {this.username = username; }public String getPassword() {return password; }public void setPassword(String password) {this.password = password; }public Date getBirthday() {return birthday; }public void setBirthday(Date birthday) {this.birthday = birthday; }}

创建UserMapper接口

package com.zg.mapper; import com.zg.domain.User; import java.util.List; public interface UserMapper {public List findAll(); }

配置UserMapper.xml

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

测试

@Test//测试一对多public void test2() throws IOException {InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml"); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream); SqlSession sqlSession = sqlSessionFactory.openSession(); UserMapper mapper = sqlSession.getMapper(UserMapper.class); List userList = mapper.findAll(); for (User user : userList) {System.out.println(user); }sqlSession.close(); }

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多对多查询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：查询用户同时查询该用户的所有角色

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select * from user u,sys_user_role ur ,sys_role r where u.id=ur.userId and ur.roleId=r.id

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创建Role实体，修改User实体

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添加UserMapper接口

package com.zg.mapper; import com.zg.domain.User; import java.util.List; public interface UserMapper {public List findAll(); public List findUserAndRoleAll(); }

配置UserMapper.xml

select * from user u,sys_user_role ur ,sys_role r where u.id=ur.userId and ur.roleId=r.id

测试代码

@Test//测试多对多public void test3() throws IOException {InputStream resourceAsStream = Resources.getResourceAsStream("sqlMapConfig.xml"); SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(resourceAsStream); SqlSession sqlSession = sqlSessionFactory.openSession(); UserMapper mapper = sqlSession.getMapper(UserMapper.class); List userAndRoleAll = mapper.findUserAndRoleAll(); for (User user : userAndRoleAll) {System.out.println(user); }sqlSession.close(); }