1. 数据库中表的列名和实体类的属性名称不一致。
可以使用 resultMap来解决。
<select id="findAll" resultMap="UserMap">
select id,userName,age from t_user
</select>
<resultMap type="User" id="UserMap">
<!--id映射主键 property是实体类的属性名 column是表中的列名 -->
<id property="id" column="id"/>
<result property="name" column="userName"/>
<result property="age" column="age"/>
</resultMap>
2.在 mybatis 中多对一映射处理
用户表和角色表示多对一的关系
3.java 类结构
用户类:User.java
public class User implements Serializable{
private int id;
private String name;
private int age;
private int roleId;
private Role role;
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 int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public int getRoleId() {
return roleId;
}
public void setRoleId(int roleId) {
this.roleId = roleId;
}
public Role getRole() {
return role;
}
public void setRole(Role role) {
this.role = role;
}
@Override
public String toString() {
return "User [id=" + id + ", name=" + name + ", age=" + age + ", roleId=" + roleId + ", role=" + role + "]";
}
}
角色类:Role.java
public class Role {
private int id;
private String name;
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;
}
@Override
public String toString() {
return "Role [id=" + id + ", name=" + name + "]";
}
}
4.映射关系----通过sql语句将两张表关联起来
<mapper namespace="cn.sxt.vo.UserMapper">
<select id="findAll" resultMap="UserMap">
select u.id as uid,u.name as uname,u.age as uage,
roleId,r.name as rname from t_user u,t_role r
where u.roleId=r.id
</select>
<resultMap type="User" id="UserMap">
<id property="id" column="uid"/>
<result property="name" column="uname"/>
<result property="age" column="uage"/>
<result property="roleId" column="roleId"/>
<!-- 映射关联对象 -->
<association property="role" column="roleId" javaType="Role">
<id property="id" column="roleId"/>
<result property="name" column="rname"/>
</association>
</resultMap>
</mapper>
5.测试
@Test
public void testFindAll() throws IOException{
SqlSession session = MybatisUtil.getSqlSession();
List<User> list = session.selectList("cn.sxt.vo.UserMapper.findAll");
for(User u:list){
System.out.println(u);
}
session.close();
}