mybatis级联(关联)查询

1.定义四个实体。User   Role    Privilege   Resource,他们之间的对于关系为

2.需求：我通过用户名username查找出该用户对应的角色以及角色对应的权限和资源

3.实体

public class User implements Serializable {
    private String id;
    private String username;
    private String password;
    private Set<Role> role = new HashSet<Role>();

public class Role implements Serializable {
    private String id;
    private String name;
    private String des;
    private Set<Privilege> privilege = new HashSet<Privilege>();

public class Privilege implements Serializable {  private String id;  
    private String name;  private String des;
    private Set<Resource> resource = new HashSet<Resource>();  
    private Privilege parent;  private Set<Privilege> child = new HashSet<Privilege>();

public class Resource implements Serializable {
    private String id;
    private String uri;
    private String des;   

4.UserMapper.xml的查询方法为

<resultMap type="user" id="userResult">
　　<id column="id" property="id"/>
   <result column="username" property="username"/>
   <collection property="role" javaType="java.util.Set" resultMap="roleResult"/>
</resultMap>
   
<resultMap type="role" id="roleResult">
　　<id column="rid" property="id"/>
   <result column="rname" property="name"/>
   <result column="rdes" property="des"/>
   <collection property="privilege" javaType="java.util.Set" resultMap="privilegeResult"/>
</resultMap>
    
<resultMap type="privilege" id="privilegeResult">
　　<id column="pid" property="id"/>
   <result column="pname" property="name"/>
   <collection property="resource" javaType="java.util.Set" resultMap="resourceResult"/>
</resultMap>
    
<resultMap type="resource" id="resourceResult">
　　<id column="resid" property="id"/>
   <result column="resuri" property="uri"/>
</resultMap>

<select id="findUserByUserName" parameterType="string" resultMap="userResult">
　　select u.id,u.username,r.id as rid,r.name as rname,r.des as rdes,p.id as pid,p.name as pname,res.id as resid,res.uri as resuri
　　from tb_user u 
  　left join user_role ur on ur.user_id=u.id
  　join tb_role r on r.id=ur.role_id
 　 join role_privilege rp on rp.role_id=r.id
 　 join tb_privilege p on p.id=rp.privilege_id
　　join tb_resource res on res.privilege_id=p.id
　　where u.username=#{username}
</select>

5.UserMapper.java定义方法

@Component
public interface UserMapper {
    User findUserByUserName(@Param(value="username")String username);
}

一对一查询
<resultMap id="blogResult" type="Blog">  
     <id property="id" column="blog_id"/>  
      <result property="title" column="blog_title"/>  
        
      <!-- 和一个用户关联,Blog 类里面属性时author,关联的列是原先的blog.author_id-->  
      <association property="author"  column="blog_author_id" javaType="Author"  resultMap="authorResult"/>  
</resultMap>  
  
<resultMap id="authorResult" type="Author">  
          <id property="id" column="author_id"/>  
          <result property="username" column="author_username"/>  
          <result property="password" column="author_password"/>  
          <result property="email" column="author_email"/>  
          <result property="bio" column="author_bio"/>  
</resultMap>  

<resultMap id="blogResult" type="Blog">  
     <id property="id" column="blog_id"/>  
      <result property="title" column="blog_title"/>  
        
      <!-- 和一个用户关联,Blog 类里面属性时author,关联的列是原先的blog.author_id-->  
      <association property="author"  column="blog_author_id" javaType="Author" >  
              <id property="id" column="author_id"/>  
              <result property="username" column="author_username"/>  
              <result property="password" column="author_password"/>  
              <result property="email" column="author_email"/>  
              <result property="bio" column="author_bio"/>  
      </association>  
</resultMap>