使用mybaits一对多表查询

来源：互联网发布：青年政治学院知乎编辑：程序博客网时间：2024/05/12 23:08

使用mybaits进行表的一对多表查询：

1.先在数据库里面写两张表，User(用户表)，Post(数据表)

post表里面要实现Serializable（序列化）

user表的实体类代码：

public class User {
   private int id;
   private String name;
   private int age;
   private String sex;
   private List<Post> posts;
   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 String getSex() {
       return sex;
   }
   public void setSex(String sex) {
       this.sex = sex;
   }
   public List<Post> getPosts() {
       return posts;
   }
   public void setPosts(List<Post> posts) {
       this.posts = posts;
   }

Post实体类的代码：

public class Post implements Serializable {
   public int getPost_id() {
       return post_id;
   }
   public void setPost_id(int post_id) {
       this.post_id = post_id;
   }
   public User getUser() {
       return user;
   }
   public void setUser(User user) {
       this.user = user;
   }
   public String getTent() {
       return tent;
   }
   public void setTent(String tent) {
       this.tent = tent;
   }
   public String getTime() {
       return time;
   }
   public void setTime(String time) {
       this.time = time;
   }
   private int post_id;
   private User user;
   private String tent;
   private String time;
}

2.在编写代码的工具里面，编写用户表和数据表相对应的实体类，编写user表的映射文件。

特别注意：<resultMap id="给ID名" type=“实体类”>

</resultMap>

<mapper namespace="com.zhiyuan.model">
   <resultMap type="Post" id="resultPostsMap">
   <result property="post_id" column="post_id"/>
   <result property="tent" column="tent"/>
   <result property="time" column="time"/>
   <association property="user" javaType="User">
   <id property="id" column="id"/>
   <result property="name" column="name"/>
   <result property="age" column="age"/>
   <result property="sex" column="sex"/>
   </association>
   </resultMap>

   <select id="getPosts" resultMap="resultPostsMap" parameterType="int">
   SELECT u.*,p.*
   FROM user u, post p
   WHERE u.id=p.userid AND p.post_id=#{post_id} ;
   </select>
</mapper>

3.编写config配置文件。

特别注意：这章的内容要配置三个文件；一个是主配置文件config,其他两个就是实体类的映射文件user.xml。

<typeAliases> 这个标签内容，它就是用于定义一个 JavaBean 类的别名

4.编写测试类。

public class Mapping {
   private static Reader reader;
   private static SqlSessionFactory sqlSessionFactory;

   static{
       try {
           reader=Resources.getResourceAsReader("config.xml");
           sqlSessionFactory=new SqlSessionFactoryBuilder().build(reader);
       } catch (IOException e) {
           // TODO Auto-generated catch block
           e.printStackTrace();
       }

   }
   public static void main(String[] args) {
       SqlSession session=sqlSessionFactory.openSession();
       int post_id=1;
       Post post=session.selectOne("com.zhiyuan.model.getPosts",post_id);
       System.out.println("tent:"+post.getTent());
       System.out.println("time:"+post.getTime());
   }

}

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