當(dāng)前位置：首頁 > 编程资源 > 编程问答 >内容正文

编程问答

mybatis关联查询

發(fā)布時(shí)間：2024/9/21 编程问答 43 豆豆

生活随笔收集整理的這篇文章主要介紹了 mybatis关联查询小編覺得挺不錯(cuò)的,現(xiàn)在分享給大家,幫大家做個(gè)參考.

一、一對(duì)一關(guān)聯(lián)

?1.1、提出需求

　　根據(jù)班級(jí)id查詢班級(jí)信息(帶老師的信息)

1.2、創(chuàng)建表和數(shù)據(jù)

　　創(chuàng)建一張教師表和班級(jí)表，這里我們假設(shè)一個(gè)老師只負(fù)責(zé)教一個(gè)班，那么老師和班級(jí)之間的關(guān)系就是一種一對(duì)一的關(guān)系。

1 CREATE TABLE teacher(2 t_id INT PRIMARY KEY AUTO_INCREMENT, 3 t_name VARCHAR(20)4 );5 CREATE TABLE class(6 c_id INT PRIMARY KEY AUTO_INCREMENT, 7 c_name VARCHAR(20), 8 teacher_id INT9 ); 10 ALTER TABLE class ADD CONSTRAINT fk_teacher_id FOREIGN KEY (teacher_id) REFERENCES teacher(t_id); 11 12 INSERT INTO teacher(t_name) VALUES('teacher1'); 13 INSERT INTO teacher(t_name) VALUES('teacher2'); 14 15 INSERT INTO class(c_name, teacher_id) VALUES('class_a', 1); 16 INSERT INTO class(c_name, teacher_id) VALUES('class_b', 2);

　　表之間的關(guān)系如下：

1.3、定義實(shí)體類

　　1、Teacher類，Teacher類是teacher表對(duì)應(yīng)的實(shí)體類。

1 package me.gacl.domain;2 3 /**4 * @author gacl5 * 定義teacher表對(duì)應(yīng)的實(shí)體類6 */7 public class Teacher {8 9 //定義實(shí)體類的屬性，與teacher表中的字段對(duì)應(yīng) 10 private int id; //id===>t_id 11 private String name; //name===>t_name 12 13 public int getId() { 14 return id; 15 } 16 17 public void setId(int id) { 18 this.id = id; 19 } 20 21 public String getName() { 22 return name; 23 } 24 25 public void setName(String name) { 26 this.name = name; 27 } 28 29 @Override 30 public String toString() { 31 return "Teacher [id=" + id + ", name=" + name + "]"; 32 } 33 }

　　2、Classes類，Classes類是class表對(duì)應(yīng)的實(shí)體類

1 package me.gacl.domain;2 3 /**4 * @author gacl5 * 定義class表對(duì)應(yīng)的實(shí)體類6 */7 public class Classes {8 9 //定義實(shí)體類的屬性，與class表中的字段對(duì)應(yīng) 10 private int id; //id===>c_id 11 private String name; //name===>c_name 12 13 /** 14 * class表中有一個(gè)teacher_id字段，所以在Classes類中定義一個(gè)teacher屬性， 15 * 用于維護(hù)teacher和class之間的一對(duì)一關(guān)系，通過這個(gè)teacher屬性就可以知道這個(gè)班級(jí)是由哪個(gè)老師負(fù)責(zé)的 16 */ 17 private Teacher teacher; 18 19 public int getId() { 20 return id; 21 } 22 23 public void setId(int id) { 24 this.id = id; 25 } 26 27 public String getName() { 28 return name; 29 } 30 31 public void setName(String name) { 32 this.name = name; 33 } 34 35 public Teacher getTeacher() { 36 return teacher; 37 } 38 39 public void setTeacher(Teacher teacher) { 40 this.teacher = teacher; 41 } 42 43 @Override 44 public String toString() { 45 return "Classes [id=" + id + ", name=" + name + ", teacher=" + teacher+ "]"; 46 } 47 }

1.4、定義sql映射文件classMapper.xml

1 <?xml version="1.0" encoding="UTF-8" ?>2 <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">3 6 <mapper namespace="me.gacl.mapping.classMapper">7 8  17 18  23 <select id="getClass" parameterType="int" resultMap="ClassResultMap"> 24 select * from class c, teacher t where c.teacher_id=t.t_id and c.c_id=#{id} 25 </select> 26  27 <resultMap type="me.gacl.domain.Classes" id="ClassResultMap"> 28 <id property="id" column="c_id"/> 29 <result property="name" column="c_name"/> 30 <association property="teacher" javaType="me.gacl.domain.Teacher"> 31 <id property="id" column="t_id"/> 32 <result property="name" column="t_name"/> 33 </association> 34 </resultMap> 35 36  41 <select id="getClass2" parameterType="int" resultMap="ClassResultMap2"> 42 select * from class where c_id=#{id} 43 </select> 44  45 <resultMap type="me.gacl.domain.Classes" id="ClassResultMap2"> 46 <id property="id" column="c_id"/> 47 <result property="name" column="c_name"/> 48 <association property="teacher" column="teacher_id" select="getTeacher"/> 49 </resultMap> 50 51 <select id="getTeacher" parameterType="int" resultType="me.gacl.domain.Teacher"> 52 SELECT t_id id, t_name name FROM teacher WHERE t_id=#{id} 53 </select> 54 55 </mapper>

　　在conf.xml文件中注冊(cè)classMapper.xml

1.5、編寫單元測(cè)試代碼

1 package me.gacl.test;2 3 import me.gacl.domain.Classes;4 import me.gacl.util.MyBatisUtil;5 import org.apache.ibatis.session.SqlSession;6 import org.junit.Test;7 8 public class Test3 {9 10 @Test 11 public void testGetClass(){ 12 SqlSession sqlSession = MyBatisUtil.getSqlSession(); 13 /** 14 * 映射sql的標(biāo)識(shí)字符串， 15 * me.gacl.mapping.classMapper是classMapper.xml文件中mapper標(biāo)簽的namespace屬性的值， 16 * getClass是select標(biāo)簽的id屬性值，通過select標(biāo)簽的id屬性值就可以找到要執(zhí)行的SQL 17 */ 18 String statement = "me.gacl.mapping.classMapper.getClass";//映射sql的標(biāo)識(shí)字符串 19 //執(zhí)行查詢操作，將查詢結(jié)果自動(dòng)封裝成Classes對(duì)象返回 20 Classes clazz = sqlSession.selectOne(statement,1);//查詢class表中id為1的記錄 21 //使用SqlSession執(zhí)行完SQL之后需要關(guān)閉SqlSession 22 sqlSession.close(); 23 System.out.println(clazz);//打印結(jié)果：Classes [id=1, name=class_a, teacher=Teacher [id=1, name=teacher1]] 24 } 25 26 @Test 27 public void testGetClass2(){ 28 SqlSession sqlSession = MyBatisUtil.getSqlSession(); 29 /** 30 * 映射sql的標(biāo)識(shí)字符串， 31 * me.gacl.mapping.classMapper是classMapper.xml文件中mapper標(biāo)簽的namespace屬性的值， 32 * getClass2是select標(biāo)簽的id屬性值，通過select標(biāo)簽的id屬性值就可以找到要執(zhí)行的SQL 33 */ 34 String statement = "me.gacl.mapping.classMapper.getClass2";//映射sql的標(biāo)識(shí)字符串 35 //執(zhí)行查詢操作，將查詢結(jié)果自動(dòng)封裝成Classes對(duì)象返回 36 Classes clazz = sqlSession.selectOne(statement,1);//查詢class表中id為1的記錄 37 //使用SqlSession執(zhí)行完SQL之后需要關(guān)閉SqlSession 38 sqlSession.close(); 39 System.out.println(clazz);//打印結(jié)果：Classes [id=1, name=class_a, teacher=Teacher [id=1, name=teacher1]] 40 } 41 }

?1.6、MyBatis一對(duì)一關(guān)聯(lián)查詢總結(jié)

　　MyBatis中使用association標(biāo)簽來解決一對(duì)一的關(guān)聯(lián)查詢，association標(biāo)簽可用的屬性如下：

property:對(duì)象屬性的名稱
javaType:對(duì)象屬性的類型
column:所對(duì)應(yīng)的外鍵字段名稱
select:使用另一個(gè)查詢封裝的結(jié)果

二、一對(duì)多關(guān)聯(lián)

2.1、提出需求

　　根據(jù)classId查詢對(duì)應(yīng)的班級(jí)信息,包括學(xué)生,老師

2.2、創(chuàng)建表和數(shù)據(jù)

　　在上面的一對(duì)一關(guān)聯(lián)查詢演示中，我們已經(jīng)創(chuàng)建了班級(jí)表和教師表，因此這里再創(chuàng)建一張學(xué)生表

CREATE TABLE student(s_id INT PRIMARY KEY AUTO_INCREMENT, s_name VARCHAR(20), class_id INT ); INSERT INTO student(s_name, class_id) VALUES('student_A', 1); INSERT INTO student(s_name, class_id) VALUES('student_B', 1); INSERT INTO student(s_name, class_id) VALUES('student_C', 1); INSERT INTO student(s_name, class_id) VALUES('student_D', 2); INSERT INTO student(s_name, class_id) VALUES('student_E', 2); INSERT INTO student(s_name, class_id) VALUES('student_F', 2);

2.3、定義實(shí)體類

　　1、Student類

1 package me.gacl.domain;2 3 /**4 * @author gacl5 * 定義student表所對(duì)應(yīng)的實(shí)體類6 */7 public class Student {8 9 //定義屬性，和student表中的字段對(duì)應(yīng) 10 private int id; //id===>s_id 11 private String name; //name===>s_name 12 13 public int getId() { 14 return id; 15 } 16 17 public void setId(int id) { 18 this.id = id; 19 } 20 21 public String getName() { 22 return name; 23 } 24 25 public void setName(String name) { 26 this.name = name; 27 } 28 29 @Override 30 public String toString() { 31 return "Student [id=" + id + ", name=" + name + "]"; 32 } 33 }

　　2、修改Classes類，添加一個(gè)List<Student> students屬性，使用一個(gè)List<Student>集合屬性表示班級(jí)擁有的學(xué)生，如下：

1 package me.gacl.domain;2 3 import java.util.List;4 5 /**6 * @author gacl7 * 定義class表對(duì)應(yīng)的實(shí)體類8 */9 public class Classes { 10 11 //定義實(shí)體類的屬性，與class表中的字段對(duì)應(yīng) 12 private int id; //id===>c_id 13 private String name; //name===>c_name 14 15 /** 16 * class表中有一個(gè)teacher_id字段，所以在Classes類中定義一個(gè)teacher屬性， 17 * 用于維護(hù)teacher和class之間的一對(duì)一關(guān)系，通過這個(gè)teacher屬性就可以知道這個(gè)班級(jí)是由哪個(gè)老師負(fù)責(zé)的 18 */ 19 private Teacher teacher; 20 //使用一個(gè)List<Student>集合屬性表示班級(jí)擁有的學(xué)生 21 private List<Student> students; 22 23 public int getId() { 24 return id; 25 } 26 27 public void setId(int id) { 28 this.id = id; 29 } 30 31 public String getName() { 32 return name; 33 } 34 35 public void setName(String name) { 36 this.name = name; 37 } 38 39 public Teacher getTeacher() { 40 return teacher; 41 } 42 43 public void setTeacher(Teacher teacher) { 44 this.teacher = teacher; 45 } 46 47 public List<Student> getStudents() { 48 return students; 49 } 50 51 public void setStudents(List<Student> students) { 52 this.students = students; 53 } 54 55 @Override 56 public String toString() { 57 return "Classes [id=" + id + ", name=" + name + ", teacher=" + teacher 58 + ", students=" + students + "]"; 59 } 60 }

2.4、修改sql映射文件classMapper.xml

　　添加如下的SQL映射信息

1 4 8 <select id="getClass3" parameterType="int" resultMap="ClassResultMap3">9 select * from class c, teacher t,student s where c.teacher_id=t.t_id and c.C_id=s.class_id and c.c_id=#{id} 10 </select> 11 <resultMap type="me.gacl.domain.Classes" id="ClassResultMap3"> 12 <id property="id" column="c_id"/> 13 <result property="name" column="c_name"/> 14 <association property="teacher" column="teacher_id" javaType="me.gacl.domain.Teacher"> 15 <id property="id" column="t_id"/> 16 <result property="name" column="t_name"/> 17 </association> 18  19 <collection property="students" ofType="me.gacl.domain.Student"> 20 <id property="id" column="s_id"/> 21 <result property="name" column="s_name"/> 22 </collection> 23 </resultMap> 24 25  31 <select id="getClass4" parameterType="int" resultMap="ClassResultMap4"> 32 select * from class where c_id=#{id} 33 </select> 34 <resultMap type="me.gacl.domain.Classes" id="ClassResultMap4"> 35 <id property="id" column="c_id"/> 36 <result property="name" column="c_name"/> 37 <association property="teacher" column="teacher_id" javaType="me.gacl.domain.Teacher" select="getTeacher2"></association> 38 <collection property="students" ofType="me.gacl.domain.Student" column="c_id" select="getStudent"></collection> 39 </resultMap> 40 41 <select id="getTeacher2" parameterType="int" resultType="me.gacl.domain.Teacher"> 42 SELECT t_id id, t_name name FROM teacher WHERE t_id=#{id} 43 </select> 44 45 <select id="getStudent" parameterType="int" resultType="me.gacl.domain.Student"> 46 SELECT s_id id, s_name name FROM student WHERE class_id=#{id} 47 </select>

2.5、編寫單元測(cè)試代碼

1 package me.gacl.test;2 3 import me.gacl.domain.Classes;4 import me.gacl.util.MyBatisUtil;5 import org.apache.ibatis.session.SqlSession;6 import org.junit.Test;7 8 public class Test4 {9 10 @Test 11 public void testGetClass3(){ 12 SqlSession sqlSession = MyBatisUtil.getSqlSession(); 13 /** 14 * 映射sql的標(biāo)識(shí)字符串， 15 * me.gacl.mapping.classMapper是classMapper.xml文件中mapper標(biāo)簽的namespace屬性的值， 16 * getClass3是select標(biāo)簽的id屬性值，通過select標(biāo)簽的id屬性值就可以找到要執(zhí)行的SQL 17 */ 18 String statement = "me.gacl.mapping.classMapper.getClass3";//映射sql的標(biāo)識(shí)字符串 19 //執(zhí)行查詢操作，將查詢結(jié)果自動(dòng)封裝成Classes對(duì)象返回 20 Classes clazz = sqlSession.selectOne(statement,1);//查詢class表中id為1的記錄 21 //使用SqlSession執(zhí)行完SQL之后需要關(guān)閉SqlSession 22 sqlSession.close(); 23 //打印結(jié)果：Classes [id=1, name=class_a, teacher=Teacher [id=1, name=teacher1], students=[Student [id=1, name=student_A], Student [id=2, name=student_B], Student [id=3, name=student_C]]] 24 System.out.println(clazz); 25 } 26 27 @Test 28 public void testGetClass4(){ 29 SqlSession sqlSession = MyBatisUtil.getSqlSession(); 30 /** 31 * 映射sql的標(biāo)識(shí)字符串， 32 * me.gacl.mapping.classMapper是classMapper.xml文件中mapper標(biāo)簽的namespace屬性的值， 33 * getClass4是select標(biāo)簽的id屬性值，通過select標(biāo)簽的id屬性值就可以找到要執(zhí)行的SQL 34 */ 35 String statement = "me.gacl.mapping.classMapper.getClass4";//映射sql的標(biāo)識(shí)字符串 36 //執(zhí)行查詢操作，將查詢結(jié)果自動(dòng)封裝成Classes對(duì)象返回 37 Classes clazz = sqlSession.selectOne(statement,1);//查詢class表中id為1的記錄 38 //使用SqlSession執(zhí)行完SQL之后需要關(guān)閉SqlSession 39 sqlSession.close(); 40 //打印結(jié)果：Classes [id=1, name=class_a, teacher=Teacher [id=1, name=teacher1], students=[Student [id=1, name=student_A], Student [id=2, name=student_B], Student [id=3, name=student_C]]] 41 System.out.println(clazz); 42 } 43 }

?2.6、MyBatis一對(duì)多關(guān)聯(lián)查詢總結(jié)

　　MyBatis中使用collection標(biāo)簽來解決一對(duì)多的關(guān)聯(lián)查詢，ofType屬性指定集合中元素的對(duì)象類型。

轉(zhuǎn)載于:https://www.cnblogs.com/jdbn/p/11047915.html

總結(jié)

以上是生活随笔為你收集整理的mybatis关联查询的全部?jī)?nèi)容，希望文章能夠幫你解決所遇到的問題。

如果覺得生活随笔網(wǎng)站內(nèi)容還不錯(cuò)，歡迎將生活随笔推薦給好友。

MyBatis