1.Mybatis多表查询
1.1 一对一查询
1.1.1 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
1.1.2一对一查询的语句
对应的sql语句：select * from orders o,user u where o.uid=u.id;
查询的结果如下：
1.1.3 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; }
1.1.4 创建OrderMapper接口
public interface OrderMapper { List<Order> findAll(); }
1.1.5 配置OrderMapper.xml
<mapper namespace="com.rg.mapper.OrderMapper"> <resultMap id="orderMap" type="com.rg.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> <!--结果集里面既有order类型,且order里面有个user类型的属性,所以可以看成是一个map类型--> <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：
<resultMap id="orderMap" type="com.rg.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.rg.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>
1.1.6 测试结果
OrderMapper mapper = sqlSession.getMapper(OrderMapper.class); List<Order> all = mapper.findAll(); for(Order order : all){ System.out.println(order); }
1.2 一对多查询
1.2.1 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
1.2.2 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：
1.2.3 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; }
1.2.4 创建UserMapper接口
public interface UserMapper { List<User> findAll(); }
public interface UserMapper { List<User> findAll(); }
1.2.5 配置UserMapper.xml
<mapper namespace="com.itheima.mapper.UserMapper"> <resultMap id="userMap" type="com.itheima.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.itheima.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>
1.2.6 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("----------------------------------"); }
注意:在根据数据表:1对多,设计实体类时.在一对应的的类中,建立一个集合用于存放多的一方的实体.在多的一方类中增加一个属性(本质是一的一方对象),用于表示属于哪一个.
1.3 多对多查询
1.3.1 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
1.3.2 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 user_role ur on u.id=ur.user_id
inner join role r on ur.role_id=r.id;
查询的结果如下：
1.3.3 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; }
1.3.4 添加UserMapper接口方法
List<User> findAllUserAndRole();
1.3.5 配置UserMapper.xml
<resultMap id="userRoleMap" type="com.itheima.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.rg.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 user_role ur on u.id=ur.user_id inner join role r on ur.role_id=r.id </select>
1.3.6 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("----------------------------------"); }
