前面几篇博客我们用mybatis能对单表进行增删改查操作了,也能用动态SQL书写比较复杂的sql语句。但是在实际开发中,我们做项目不可能只是单表操作,往往会涉及到多张表之间的关联操作。那么我们如何用 mybatis 处理多表之间的关联操作呢?请看本篇博客详解。
本篇详细代码:http://pan.baidu.com/s/1eSzmst8 密码:3n3o
1、一对一
我们以用户表 user 和订单表 orders 为例。设定一个订单只能由一个 用户创建,那么由订单到用户就是一对一的关系。
①、创建用户表 user 和订单表 orders
用户表 user
订单表 orders
②、创建项目工程,导入相应的 jar 包
③、创建实体类
User.java
package com.ys.po; public class User { //用户ID private int id; //用户姓名 private String username; //用户性别 private String sex; 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 getSex() { return sex; } public void setSex(String sex) { this.sex = sex; } @Override public String toString() { return "User [id=" + id + ", username=" + username + ", sex=" + sex + "]"; } }
Orders.java
package com.ys.po; public class Orders { //订单ID private int id; //用户ID private int userId; //订单数量 private String number; //和用户表构成一对一的关系,即一个订单只能由一个用户创建 private User user; public int getId() { return id; } public void setId(int id) { this.id = id; } public int getUserId() { return userId; } public void setUserId(int userId) { this.userId = userId; } public String getNumber() { return number; } public void setNumber(String number) { this.number = number; } public User getUser() { return user; } public void setUser(User user) { this.user = user; } @Override public String toString() { return "Orders [id=" + id + ", userId=" + userId + ", number=" + number + ", user=" + user + "]"; } }
④、创建 OrderMapper 接口和 OrderMapper.xml 文件
由于我们采用 Mapper 代理加载 xxxMapper.xml 文件,这里我们重复一下 Mapper 代理所需的条件,接口和xml文件必须满足以下几个条件:
1、接口必须要和 xml 文件同名且在同一个包下,也就是说 xml 文件中的namespace是接口的全类名
2、接口中的方法名和xml 文件中定义的 id 一致
3、接口输入参数类型要和xml 中定义的 parameterType 一致
4、接口返回数据类型要和xml 中定义的 resultType 一致
详细介绍参考上一篇博客:http://www.cnblogs.com/ysocean/p/7301548.html
OrderMapper 接口
package one.to.one.mapper; import com.ys.po.Orders; import com.ys.po.User; public interface OrdersMapper { /** * 方式一:嵌套结果 * select * from orders o,user u where o.user_id=u.id and o.id=#{id} * @param orderId * @return */ //根据订单ID查询订单和用户信息 public Orders selectOrderAndUserByOrderID(int orderId); /** * 方式二:嵌套查询 * select * from order WHERE id=1;//得到user_id * select * from user WHERE id=1 //1 是上一个查询得到的user_id的值 * @param userID * @return */ //根据订单ID得到订单信息(包含user_id) public Orders getOrderByOrderId(int orderId); //根据用户ID查询用户信息 public User getUserByUserId(int userID); }
OrderMapper .xml文件
<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="one.to.one.mapper.OrdersMapper"> <!-- 嵌套结果:使用嵌套结果映射来处理重复的联合结果的子集 封装联表查询的数据(去除重复的数据) select * from orders o,user u where o.user_id=u.id and o.id=#{id} --> <select id="selectOrderAndUserByOrderID" resultMap="getOrderAndUser"> select * from orders o,user u where o.user_id=u.id and o.id=#{id} </select> <resultMap type="com.ys.po.Orders" id="getOrderAndUser"> <!-- id:指定查询列表唯一标识,如果有多个唯一标识,则配置多个id column:数据库对应的列 property:实体类对应的属性名 --> <id column="id" property="id"/> <result column="user_id" property="userId"/> <result column="number" property="number"/> <!--association:用于映射关联查询单个对象的信息 property:实体类对应的属性名 javaType:实体类对应的全类名 --> <association property="user" javaType="com.ys.po.User"> <!-- id:指定查询列表唯一标识,如果有多个唯一标识,则配置多个id column:数据库对应的列 property:实体类对应的属性名 --> <id column="id" property="id"/> <result column="username" property="username"/> <result column="sex" property="sex"/> </association> </resultMap> <!-- 方式二:嵌套查询:通过执行另外一个SQL映射语句来返回预期的复杂类型 select user_id from order WHERE id=1;//得到user_id select * from user WHERE id=1 //1 是上一个查询得到的user_id的值 property:别名(属性名) column:列名 --> <select id="getOrderByOrderId" resultMap="getOrderMap"> select * from order where id=#{id} </select> <resultMap type="com.ys.po.Orders" id="getOrderMap"> <id column="id" property="id"/> <result column="number" property="number"/> <association property="userId" column="id" select="getUserByUserId"> </association> </resultMap> <select id="getUserByUserId" resultType="com.ys.po.User"> select * from user where id=#{id} </select> </mapper>
⑤、向 mybatis-configuration.xml 配置文件中注册 OrderMapper.xml 文件
<?xml version="1.0" encoding="UTF-8"?> <!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd"> <configuration> <!-- 加载数据库属性文件 --> <properties resource="db.properties"></properties> <!-- 定义别名 --> <typeAliases> <!-- mybatis自动扫描包中的po类,自动定义别名,别名是类名(首字母大写或小写都可以,一般用小写) --> <package name="com.ys.po"/> </typeAliases> <environments default="development"> <environment id="development"> <transactionManager type="JDBC"/> <!--dataSource 元素使用标准的 JDBC 数据源接口来配置 JDBC 连接对象源 --> <dataSource type="POOLED"> <property name="driver" value="${jdbc.driver}"/> <property name="url" value="${jdbc.url}"/> <property name="username" value="${jdbc.username}"/> <property name="password" value="${jdbc.password}"/> </dataSource> </environment> </environments> <mappers> <!-- 通过OrdersMapper接口注册OrdersMapper.xml文件, 必须保证:接口和xml在同一个包下,而且名字一样 OrdersMapper接口的方法名和OrdersMapper.xml文件的id一样 OrdersMapper接口的输出输出参数和OrdersMapper.xml文件resultType,parameterType类型一样 --> <mapper class="one.to.one.mapper.OrdersMapper"/> </mappers> </configuration>
⑥、测试
package one.to.one.mapper; import java.io.InputStream; import org.apache.ibatis.session.SqlSession; import org.apache.ibatis.session.SqlSessionFactory; import org.apache.ibatis.session.SqlSessionFactoryBuilder; import org.junit.Before; import org.junit.Test; import com.ys.po.Orders; public class OneToOneTest { //定义 SqlSession SqlSession session =null; @Before public void init(){ //定义mybatis全局配置文件 String resource = "mybatis-configuration.xml"; //加载 mybatis 全局配置文件 InputStream inputStream = OneToOneTest.class.getClassLoader() .getResourceAsStream(resource); //构建sqlSession的工厂 SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(inputStream); //根据 sqlSessionFactory 产生 session session = sessionFactory.openSession(); } /** * 方式一:嵌套结果 * select * from orders o,user u where o.user_id=u.id and o.id=#{id} */ @Test public void testSelectOrderAndUserByOrderId(){ String statement = "one.to.one.mapper.OrdersMapper.selectOrderAndUserByOrderID"; //创建OrdersMapper对象,mybatis自动生成mapepr代理对象 OrdersMapper orderMapper = session.getMapper(OrdersMapper.class); Orders order = orderMapper.selectOrderAndUserByOrderID(1); System.out.println(order); session.close(); } /** * 方式二:嵌套查询 * select * from order WHERE id=1;//得到user_id * select * from user WHERE id=1 //1 是上一个查询得到的user_id的值 */ @Test public void testgetOrderByOrderId(){ String statement = "one.to.one.mapper.OrdersMapper.getOrderByOrderId"; //创建OrdersMapper对象,mybatis自动生成mapepr代理对象 OrdersMapper orderMapper = session.getMapper(OrdersMapper.class); Orders order = orderMapper.selectOrderAndUserByOrderID(1); System.out.println(order); session.close(); } }
2、一对多
还是以用户表 user 和 订单表 orders 为例,一个用户能创建多个订单。故用户和订单构成一对多的关联。
我们在 user.java 中添加一个属性 public List<Orders> orders;
①、创建实体类
user.java如下,orders.java保持不变
package com.ys.po; import java.util.List; public class User { //用户ID private int id; //用户姓名 private String username; //用户性别 private String sex; //一个用户能创建多个订单,用户和订单构成一对多的关系 public List<Orders> orders; public List<Orders> getOrders() { return orders; } public void setOrders(List<Orders> orders) { this.orders = orders; } 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 getSex() { return sex; } public void setSex(String sex) { this.sex = sex; } @Override public String toString() { return "User [id=" + id + ", username=" + username + ", sex=" + sex + "]"; } }
②、创建 UserMapper 接口和 UserMapper.xml 文件
UserMapper接口
package one.to.many.mapper; import com.ys.po.User; public interface UserMapper { //根据用户id查询用户信息,以及用户下面的所有订单信息 public User selectUserAndOrdersByUserId(int UserId); }
UserMapper.xml
<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="one.to.many.mapper.UserMapper"> <!-- 方式一:嵌套结果:使用嵌套结果映射来处理重复的联合结果的子集 封装联表查询的数据(去除重复的数据) select * from user u,orders o where u.id=o.user_id and u.id=#{id} --> <select id="selectUserAndOrdersByUserId" resultMap="getUserAndOrders"> select u.*,o.id oid,o.number number from user u,orders o where u.id=o.user_id and u.id=#{id} </select> <resultMap type="com.ys.po.User" id="getUserAndOrders"> <!--id:指定查询列表唯一标识,如果有多个唯一标识,则配置多个id column:数据库对应的列 property:实体类对应的属性名 --> <id column="id" property="id"/> <result column="username" property="username"/> <result column="sex" property="sex"/> <!-- property:实体类中定义的属性名 ofType:指定映射到集合中的全类名 --> <collection property="orders" ofType="com.ys.po.Orders"> <id column="oid" property="id"/> <result column="number" property="number"/> </collection> </resultMap> </mapper>
③、向 mybatis-configuration.xml 配置文件中注册 UserMapper.xml 文件
④、测试
@Test public void testSelectOrderAndUserByOrderId(){ String statement = "one.to.many.mapper.UserMapper.selectUserAndOrdersByUserId"; //创建OrdersMapper对象,mybatis自动生成mapepr代理对象 UserMapper userMapper = session.getMapper(UserMapper.class); User user = userMapper.selectUserAndOrdersByUserId(1); System.out.println(user.getOrders().size()); session.close(); }
3、多对多
这里我们以用户 user 表和 角色role 表为例,假定一个用户能被分配成多重角色,而一种角色也能分给多个用户,故用户和角色构成多对多的关系。
需求:给定角色id,查询这个角色所属的所有用户信息
①、在数据库中建立相应的表
user 表和上面的保持不变
role 表
两者之间的关联表user_role
②、建立对应的实体类
User.java
Role.java
package com.ys.po; import java.util.List; public class Role { private int id; private String name; private List<User> users; public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public List<User> getUsers() { return users; } public void setUsers(List<User> users) { this.users = users; } }
User_Role.java
package com.ys.po; public class User_Role { private User user; private Role role; public User getUser() { return user; } public void setUser(User user) { this.user = user; } public Role getRole() { return role; } public void setRole(Role role) { this.role = role; } }
③、创建 UserMapper 接口和 UserMapper.xml 文件
UserMapper 接口
package many.to.many.mapper; import java.util.List; import com.ys.po.User; public interface UserMapper { //给定一个角色id,要得到具有这个角色的所有用户信息 public List<User> getUserByRoleId(int roleId); }
UserMapper.xml
<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd"> <mapper namespace="many.to.many.mapper.UserMapper"> <select id="getUserByRoleId" resultMap="getUserMap"> select * from user_role ur,user u where ur.user_id=u.id and ur.role_id=#{id} </select> <resultMap type="com.ys.po.User" id="getUserMap"> <id column="id" property="id"/> <result column="username" property="username"/> <result column="sex" property="sex"/> </resultMap> </mapper>
④、向 mybatis-configuration.xml 配置文件中注册 UserMapper.xml 文件
⑤、测试
@Test public void testGetUserByRoleId(){ String statement = "many.to.many.mapper.UserMapper.getUserByRoleId"; //创建OrdersMapper对象,mybatis自动生成mapepr代理对象 UserMapper userMapper = session.getMapper(UserMapper.class); List<User> users = userMapper.getUserByRoleId(1); session.close(); }
多对多主要是关联关系要找好,然后根据关联去查询。