Mybatis中注解方式实现一对多查询

上一篇关于mybatis的记录了如何查询user这个实体类的数据。假设这些用户分属于不同的工作部门，今天记录实现查询部门及下属用户的过程。据此，新建一个mysql的 table，名为department_，字段为id，name。代码略。

在com.mybatis.pojo下面建立一个Department.java的实体类。属性包括id，name，users，为其设置setter和getter。

另外，在上一篇记录到的user_的table中，增加字段did，表示某用户所属部门的id。给User.java设置属性Departmet,和对应的setter与getter，代码略。

由于采用注解的方式，所以要建立名为UserMapper和DepartmentMapper的interface。

代码如下

User对department是多对一

package com.mybatis.mapper;

import java.util.List;
import org.apache.ibatis.annotations.One;

import org.apache.ibatis.annotations.Delete;
import org.apache.ibatis.annotations.Insert;
import org.apache.ibatis.annotations.Result;
import org.apache.ibatis.annotations.Results;
import org.apache.ibatis.annotations.Select;
import org.apache.ibatis.annotations.Update;

import com.mybatis.pojo.User;

public interface UserMapper {
	
	@Insert(" insert into user_ (name,usercode,did) values(#{name},#{usercode},#{did})")
	public int add(User user);
	
	@Delete("select * from user_ where id = #{id}")
	public void delete(int id);
	
	@Update("update user_ set name=#{name} , usercode=#{usercode} , did = #{did} where id = #{id}")
	public int update(User user);
	
	@Select("select * from user_")
	@Results({
		@Result(property="department",column="did",one=@One(select="com.mybatis.mapper.DepartmentMapper.get"))
	})
	public List<User> list();
	
	@Select("select * from user_ where id = #{id}")
	public User get(int id);
	
	@Select("select * from user_ where did = #{did}")
	public List<User> listByDepartment(int did);
}

department对user是一对多

package com.mybatis.mapper;

import java.util.List;

import org.apache.ibatis.annotations.Delete;
import org.apache.ibatis.annotations.Insert;
import org.apache.ibatis.annotations.Many;
import org.apache.ibatis.annotations.Result;
import org.apache.ibatis.annotations.Results;
import org.apache.ibatis.annotations.Select;
import org.apache.ibatis.annotations.Update;

import com.mybatis.pojo.Department;

public interface DepartmentMapper {
	
	@Insert("insert into department_ (name) values(#{name})")
	public int add(Department department);
	
	@Delete("delete from department_ where id = #{id}")
	public void delete(int id);
	
	@Select("select * from department_")
	@Results({
		@Result(property="id",column="id"),
		@Result(property="users",javaType=List.class,column="id",many=@Many(select = "com.mybatis.mapper.UserMapper.listByDepartment"))	
	})
	public List<Department> list();
	
	@Select("select * from department_ where id = #{id}")
	public Department get(int id);
	
	@Update("update department_ set name = #{name} where id = #{id}")
	public int update(Department department);
}

写完两个Mapper，要在mybatis-config.xml里面写上<mapper class="com.mybatis.mapper.DepartmentMapper"/>

最后编写测试类

package com.mybatis;

import java.io.IOException;
import java.io.InputStream;
import java.util.List;

import org.apache.ibatis.io.Resources;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;

import com.mybatis.mapper.DepartmentMapper;
import com.mybatis.mapper.UserMapper;
import com.mybatis.pojo.Department;
import com.mybatis.pojo.User;

public class TestMybatisM2M {
	public static void main(String[] args) throws IOException{
		String resource = "mybatis-config.xml";
		InputStream inputStream = Resources.getResourceAsStream(resource);
		SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
		SqlSession session = sqlSessionFactory.openSession();
		
		DepartmentMapper mapper = session.getMapper(DepartmentMapper.class);
		listAll(mapper);
		session.commit();
		session.close();
	}

	private static void listAll(DepartmentMapper mapper) {
		// TODO Auto-generated method stub
		List<Department> ds = mapper.list();
		for(Department d:ds){
			System.out.println(d.getName());
			List<User> us = d.getUsers();
			for(User u:us){
				System.out.println("\t"+u.getName()+"\t"+u.getUsercode());
			}
		}
	}
}

控制台结果

DEBUG [main] - ==> Preparing: select * from department_
DEBUG [main] - ==> Parameters:
TRACE [main] - <== Columns: id, name
TRACE [main] - <== Row: 1, technique
DEBUG [main] - ====> Preparing: select * from user_ where did = ?
DEBUG [main] - ====> Parameters: 1(Integer)
TRACE [main] - <==== Columns: id, name, usercode, did
TRACE [main] - <==== Row: 1, tom123, 180923001, 1
TRACE [main] - <==== Row: 2, serenity, 180923101, 1
DEBUG [main] - <==== Total: 2
DEBUG [main] - <== Total: 1
technique
tom123 180923001
serenity 180923101

Mybatis中注解方式实现一对多查询

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