MyBatis（三）---實現一對一和一對多的關聯表查詢
阿新 • • 發佈：2018-12-25
（1） 一對一的關聯表查詢
新建class表和teacher表，表結構如下：
class：
teacher:
在兩張表裡面填寫一些資料：
資料庫準備工作完成後，新建一個JAVA專案，工程目錄、類和所需的JAR包如下：
新建db.properties，裡面存放連線資料庫的鍵值對：
driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/mybase
username=root
password=123456新建和teacher表對應的實體類Teacherpackage com.lcb.user; import java.util.List; public class Classes { private int id; private String name; private Teacher teacher; //private List<Student> student; 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 Teacher getTeacher() { return teacher; } public void setTeacher(Teacher teacher) { this.teacher = teacher; } /*public List<Student> getStudent() { return student; }*/ /*public void setStudent(List<Student> student) { this.student = student; }*/ @Override public String toString() { return "Classes [id=" + id + ", name=" + name + ", teacher=" + teacher + "]"; } }
新建userMapper.xml用於對映SQL語句：package com.lcb.user; public class Teacher { private int id; // id-->t_id private String name;//name-->t_name 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; } @Override public String toString() { return "teacher [id=" + id + ", name=" + name + "]"; } }
<?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.lcb.mapping.userMapper"> <select id="getClass" parameterType="int" resultMap="ClassesResultMap"> select * from class c,teacher t where c.teacher_id=t.t_id and c.c_id=#{id} </select> <resultMap type="com.lcb.user.Classes" id="ClassesResultMap"> <!-- 實體類的欄位名和資料表的欄位名對映 --> <id property="id" column="c_id"/> <result property="name" column="c_name"/> <association property="teacher" javaType="com.lcb.user.Teacher"> <id property="id" column="t_id"/> <result property="name" column="t_name"/> </association> </resultMap> </mapper>
新建conf.xml，用於配置資料庫連線:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<!-- 匯入db.properties檔案裡面資料庫的鍵值對資訊 -->
<properties resource="db.properties"/>
<environments default="development">
<environment id="development">
<transactionManager type="JDBC"/>
<dataSource type="POOLED">
<property name="driver" value="${driver}"/>
<property name="url" value="${url}"/>
<property name="username" value="${username}"/>
<property name="password" value="${password}"/>
</dataSource>
</environment>
</environments>
<mappers>
<mapper resource="com/lcb/mapping/userMapper.xml"/>
</mappers>
</configuration>新建Test.java用於測試：
package com.lcb.user;
import java.io.InputStream;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
public class Test {
public static void main(String[] args){
//mybatis配置檔案
String resource = "com/lcb/jdbc/conf.xml";
//使用類載入器載入mybatis配置檔案（它也載入關聯的對映檔案）
InputStream is = Test.class.getClassLoader().getResourceAsStream(resource);
//構建SqlSession的工廠
SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(is);
//獲取SqlSession物件
SqlSession sqlSession = sessionFactory.openSession();
String statement = "com.lcb.mapping.userMapper.getClass";
//查詢結果：Classes [id=1, name=a, teacher=teacher [id=1, name=jack]]
Classes classes = sqlSession.selectOne(statement,1);
sqlSession.close();
System.out.println(classes);
}
}
將查詢class表中c_id=1的資料，並關聯teacher表，查詢結果：
Classes [id=1, name=a, teacher=teacher [id=1, name=jack]]
（2） 一對多的關聯表查詢
在之前的基礎上，再新建一張student表：
下面將查詢class表，並關聯teacher表和student表，查詢出班級對應的老師和學生
新建和student表對應的實體類Student
package com.lcb.user;
public class Student {
private int id; //id-->s_id
private String name; //name-->s_name
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;
}
@Override
public String toString() {
return "Student [id=" + id + ", name=" + name + "]";
}
}
在原來的Classes.java中，定義一個List集合的Student，修改後程式碼如下：
package com.lcb.user;
import java.util.List;
public class Classes {
private int id;
private String name;
private Teacher teacher;
private List<Student> student;
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 Teacher getTeacher() {
return teacher;
}
public void setTeacher(Teacher teacher) {
this.teacher = teacher;
}
public List<Student> getStudent() {
return student;
}
public void setStudent(List<Student> student) {
this.student = student;
}
@Override
public String toString() {
return "Classes [id=" + id + ", name=" + name + ", teacher=" + teacher + ", student=" + student + "]";
}
}
<?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.lcb.mapping.userMapper">
<!-- 一對一關聯查詢 -->
<select id="getClass" parameterType="int" resultMap="ClassesResultMap">
select * from class c,teacher t where c.teacher_id=t.t_id and c.c_id=#{id}
</select>
<resultMap type="com.lcb.user.Classes" id="ClassesResultMap">
<!-- 實體類的欄位名和資料表的欄位名對映 -->
<id property="id" column="c_id"/>
<result property="name" column="c_name"/>
<association property="teacher" javaType="com.lcb.user.Teacher">
<id property="id" column="t_id"/>
<result property="name" column="t_name"/>
</association>
</resultMap>
<!-- 一對多關聯查詢 -->
<select id="getClass2" parameterType="int" resultMap="ClassesResultMap2">
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}
</select>
<resultMap type="com.lcb.user.Classes" id="ClassesResultMap2">
<id property="id" column="c_id"/>
<result property="name" column="c_name"/>
<association property="teacher" javaType="com.lcb.user.Teacher">
<id property="id" column="t_id"/>
<result property="name" column="t_name"/>
</association>
<collection property="student" ofType="com.lcb.user.Student">
<id property="id" column="s_id"/>
<result property="name" column="s_name"/>
</collection>
</resultMap>
</mapper>package com.lcb.user;
import java.io.InputStream;
import org.apache.ibatis.session.SqlSession;
import org.apache.ibatis.session.SqlSessionFactory;
import org.apache.ibatis.session.SqlSessionFactoryBuilder;
public class Test {
public static void main(String[] args){
//mybatis配置檔案
String resource = "com/lcb/jdbc/conf.xml";
//使用類載入器載入mybatis配置檔案（它也載入關聯的對映檔案）
InputStream is = Test.class.getClassLoader().getResourceAsStream(resource);
//構建SqlSession的工廠
SqlSessionFactory sessionFactory = new SqlSessionFactoryBuilder().build(is);
//獲取SqlSession物件
SqlSession sqlSession = sessionFactory.openSession();
String statement = "com.lcb.mapping.userMapper.getClass2";
Classes classes = sqlSession.selectOne(statement,1);
sqlSession.close();
System.out.println(classes);
}
}
Classes [id=1, name=a, teacher=teacher [id=1, name=jack], student=[Student [id=1, name=lcb], Student [id=2, name=ty], Student [id=4, name=ayb]]]