一对一查询:
对应的sql语句：select * from orders o,user u where o.uid=u.id;
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;
}
创建OrderMapper接口
public interface OrderMapper {
List<Order> findAll();
}
配置OrderMapper.xml
<mapper namespace="com.itheima.mapper.OrderMapper">
<resultMap id="orderMap" type="order">
<!--手动指定字段与实体属性的映射关系
column: 数据表的字段名称
property：实体的属性名称 -->
<id column="oid" property="id"></id>
<result column="ordertime" property="ordertime"></result>
<result column="total" property="total"></result>
<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,u.id uid FROM orders o,USER u WHERE o.uid=u.id
</select>
</mapper>
其中<resultMap>还可以配置如下：
<resultMap id="orderMap" type="order">
<result property="id" column="id"></result>
<result property="ordertime" column="ordertime"></result>
<result property="total" column="total"></result>
<!--
property: 当前实体(order)中的属性名称(private User user)
javaType: 当前实体(order)中的属性的类型(User)
-->
<association property="user" javaType="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:
一对多查询:
对应的sql语句：select *,o.id oid from user u,orders o WHERE u.id = o.uid
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;
}
创建UserMapper接口:
public interface UserMapper {
List<User> findAll();
}
配置UserMapper.xml
<resultMap id="userMap" type="user">
<id column="uid" property="id"></id>
<result column="username" property="username"></result>
<result column="password" property="password"></result>
<result column="birthday" property="birthday"></result>
<!--配置集合信息
property:集合名称
ofType：当前集合中的数据类型-->
<collection property="orderList" ofType="order">
<!--封装order的数据-->
<id column="oid" property="id"></id>
<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,orders o WHERE u.id = o.uid
</select>
测试结果
多对多查询
对应的sql语句：select * from user u,sys_user_role ur,sys_role r where u.id=ur.userId and ur.roleId=r.id
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;
//描述的是当前用户具备哪些角色
private List<Role> roleList;
}
public class Role {
private int id;
private String roleName;
private String roleDesc;
}
添加UserMapper接口方法
List<User> findAllUserAndRole();
配置UserMapper.xml
<resultMap id="userRoleMap" type="user">
<!--user的信息-->
<id column="userId" property="id"></id>
<result column="username" property="username"></result>
<result column="password" property="password"></result>
<result column="birthday" property="birthday"></result>
<!--user内部的roleList信息-->
<collection property="roleList" ofType="role">
<id column="roleId" property="id"></id>
<result column="roleName" property="roleName"></result>
<result column="roleDesc" property="roleDesc"></result>
</collection>
</resultMap>
<select id="findUserAndRoleAll" resultMap="userRoleMap">
select * from user u,sys_user_role ur,sys_role r where u.id=ur.userId and ur.roleId=r.id
</select>
知识小结
MyBatis多表配置方式：
一对一配置：使用<resultMap>做配置
一对多配置：使用<resultMap>+<collection>做配置
多对多配置：使用<resultMap>+<collection>做配置
Mybatis的注解开发:
MyBatis的常用注解:
@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:
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
<mappers>
<!--扫描使用注解的类-->
<mapper class="com.itheima.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
<mappers>
<!--扫描使用注解的类所在的包-->
<package name="com.itheima.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<resultMap>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:
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.itheima.mapper.UserMapper.findById"))
})
List<Order> findAll();
}
public interface UserMapper {
@Select("select * from user where id=#{id}")
User findById(int id);
}
@Test
//测试结果
public void testSelectOrderAndUser() {
List<Order> all = orderMapper.findAll();
for(Order order : all){
System.out.println(order);
}
}
一对多查询:
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.itheima.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
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:
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.itheima.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
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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