7. MyBatis one-to-many queries

One: the preparatory work

1. Building Data

CREATE TABLE Boss (b_id INT (one) PRIMARY KEY auto_increment not null,b_name VARCHAR (255)); CREATE TABLE Manager (m_id INT) PRIMARY KEY auto_increment not null,m_name VARCHAR (255)); INSERT into Boss (B_name) VALUES (' Tom '); INSERT into Manager (M_name) VALUES (' Mgr1 '), insert into Manager (M_name) VALUES (' Mgr2 '), insert into manager (m_ Name) VALUES (' Mgr3 ');

2. Establishing the corresponding entity class

Package Com.mybatis.entities;public class Manager {private Integer id;private String name;//provides the corresponding Getter/setter method//provides T Ostring Method}================================package Com.mybatis.entities;import Java.util.list;public class Boss { Private Integer id;private String name;private list<manager> mgrs;//provide the appropriate Getter/setter method//Provide toString method}

3. Create a corresponding SQL mapping file

Only the boss is queried here and then all the managers under the boss are identified, so only the boss mapping file is established.

Two: Test

     1. Write the SQL statement in Bossmapper.xml, and the corresponding configuration

<?xml version= "1.0"  encoding= "UTF-8"? ><! doctype mapper public  "-//mybatis.org//dtd mapper 3.0//en"   "http://mybatis.org/ Dtd/mybatis-3-mapper.dtd "> <mapper namespace=" Com.mybatis.entities.BossMapper "><!--   Query methods There are two types of, ::1.  nested results, which use nested result mappings to process subsets of duplicate federated results to encapsulate data from a table query (removing duplicate data) 2.  Nested query: Returns the expected complex type by executing another SQL mapping statement  -->  <!--  test   nested results  --> <!--  Because there is an object in the return value,  only the alias is used to map the unavailable,  This uses a custom return value type to map  --> <select id= "GetBoss1"   parametertype= "int"  resultmap= "Getboss1map" > SELECT * FROM boss b,  manager m where b.b_id=m.b_id and b.b_id=#{b_id} </select> <!--   id:  must correspond to the  resultmap= "Getstundet1map"   above  type:  Specify the return value type,  can be understood as  select label resulttype  --> <resultmap type= "Boss"  id= "GetBoss1Map" >&Nbsp;<id column= "b_id"  property= "id"/> <result column= "b_name"  property= " Name "/> <!-- oftype Specifies the object type in the students collection  --> <collection property=" Mgrs "  oftype= "Manager" > <id column= "m_id"  property= "id"/> <result column= "M_name"  property= "name"/> </collection> </resultmap>  <!--  test   Nested queries  --> <!--  Because there is an object in the return value,  so only the alias is used to map the unavailable,  This uses a custom return value type to map  -->  <select id= "GetBoss2"  parametertype= "int"  resultmap= "Getboss2map" > select  b_id, b_name FROM boss WHERE b_id=#{b_id} </select> <!--   Use aliases to map attributes in entity classes  --> <select id= "GetManager"  parametertype= "int"   Resulttype= "Teacher" > SELECT m_id id, m_name name FROM manager  Where b_id=#{b_id} </seleCt> <resultmap type= "Boss"  id= "Getboss2map" > <id column= "b_id"   property= "id"/> <result column= "b_name"  property= "name"/> <collection  Property= "Mgrs"  column= "b_id"  oftype= "Manager"  select= "GetManager" ></collection>  </resultMap> </mapper>

2. Code Testing

Package Com.mybatis.test;import Org.apache.ibatis.session.sqlsession;import Org.junit.test;import Com.mybatis.entities.boss;import Com.mybatis.util.mybatisutil;public class Testboss {@Testpublic void TestGetBoss1 () {sqlsession session = Mybatisutil.getsqlsession (); String statement = "Com.mybatis.entities.BossMapper.getBoss1"; Boss Boss = Session.selectone (statement, 1); SYSTEM.OUT.PRINTLN (boss);} @Testpublic void TestGetBoss2 () {sqlsession session = Mybatisutil.getsqlsession (); String statement = "Com.mybatis.entities.BossMapper.getBoss2"; Boss Boss = Session.selectone (statement, 1); SYSTEM.OUT.PRINTLN (Boss);}}

Complete the test!

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7. MyBatis one-to-many queries