CREATE TABLE teacher( t_id INT PRIMARY KEY AUTO_INCREMENT, t_name VARCHAR(20) ); CREATE TABLE class( c_id INT PRIMARY KEY AUTO_INCREMENT, c_name VARCHAR(20), teacher_id INT ); ALTER TABLE class ADD CONSTRAINT fk_teacher_id FOREIGN KEY (teacher_id) REFERENCES teacher(t_id); INSERT INTO teacher(t_name) VALUES('LS1'); INSERT INTO teacher(t_name) VALUES('LS2'); INSERT INTO class(c_name, teacher_id) VALUES('bj_a', 1); INSERT INTO class(c_name, teacher_id) VALUES('bj_b', 2); 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('xs_A', 1); INSERT INTO student(s_name, class_id) VALUES('xs_B', 1); INSERT INTO student(s_name, class_id) VALUES('xs_C', 1); INSERT INTO student(s_name, class_id) VALUES('xs_D', 2); INSERT INTO student(s_name, class_id) VALUES('xs_E', 2); INSERT INTO student(s_name, class_id) VALUES('xs_F', 2);
package com.hb.bean; import java.util.List; public class Classes { private int id; private String name; private Teacher teacher; private List<Student> students; 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> getStudents() { return students; } public void setStudents(List<Student> students) { this.students = students; } @Override public String toString() { return "Classes [id=" + id + ", name=" + name + ", teacher=" + teacher + ", students=" + students + "]"; } }
package com.hb.bean; public class Student { private int id; private String 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 + "]"; } }
package com.hb.bean; public class Teacher { private int id; private String 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.hb.bean.classesMapper"> <!-- 这里namespace必须是“包名 + xml文件名”,不然要运行的时候要报错 “is not known to the MapperRegistry” --> <!-- 方式一: 嵌套结果: 使用嵌套结果映射来处理重复的联合结果的子集 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=1 --> <select id="getClass3" parameterType="int" resultMap="ClassResultMap3"> 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.hb.bean.Classes" id="ClassResultMap3"> <id property="id" column="c_id" /> <result property="name" column="c_name" /> <association property="teacher" column="teacher_id" javaType="com.hb.bean.Teacher"> <id property="id" column="t_id" /> <result property="name" column="t_name" /> </association> <!-- ofType指定students集合中的对象类型 --> <collection property="students" ofType="com.hb.bean.Student"> <id property="id" column="s_id" /> <result property="name" column="s_name" /> </collection> </resultMap> <!-- 方式二:嵌套查询:通过执行另外一个SQL映射语句来返回预期的复杂类型 SELECT * FROM class WHERE c_id=1; SELECT * FROM teacher WHERE t_id=1 //1 是上一个查询得到的teacher_id的值 SELECT * FROM student WHERE class_id=1 //1是第一个查询得到的c_id字段的值 --> <select id="getClass4" parameterType="int" resultMap="ClassResultMap4"> select * from class where c_id=#{id} </select> <resultMap type="com.hb.bean.Classes" id="ClassResultMap4"> <id property="id" column="c_id" /> <result property="name" column="c_name" /> <association property="teacher" column="teacher_id" javaType="com.hb.bean.Teacher" select="getTeacher2"></association> <collection property="students" ofType="com.hb.bean.Student" column="c_id" select="getStudent"></collection> </resultMap> <select id="getTeacher2" parameterType="int" resultType="com.hb.bean.Teacher"> SELECT t_id id, t_name name FROM teacher WHERE t_id=#{id} </select> <select id="getStudent" parameterType="int" resultType="com.hb.bean.Student"> SELECT s_id id, s_name name FROM student WHERE class_id=#{id} </select> </mapper>
package com.hb.test3; import java.io.InputStream; import org.apache.ibatis.session.SqlSession; import org.apache.ibatis.session.SqlSessionFactory; import org.apache.ibatis.session.SqlSessionFactoryBuilder; import org.junit.Before; import org.junit.Test; import com.hb.bean.Classes; public class Test3 { public static SqlSessionFactory sqlSessionFactory; public static SqlSession sqlSession; @Before public void init(){ //"/"表示是在src根目录下 String source = "config.xml"; InputStream inputStream = Test3.class.getClassLoader().getResourceAsStream(source); try { sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); // sqlSession = sqlSessionFactory.openSession(); //是否自动提交,默认不是自动提交的 sqlSession = sqlSessionFactory.openSession(true); } catch (Exception e) { e.printStackTrace(); } } @Test public void selectById(){ String statment = "com.hb.bean.classesMapper.getClass3"; Classes classes = sqlSession.selectOne(statment, 1); System.out.println(classes); } @Test public void selectById2(){ String statment = "com.hb.bean.classesMapper.getClass4"; Classes classes = sqlSession.selectOne(statment, 1); System.out.println(classes); } }
<?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> <settings> <!-- changes from the defaults for testing --> <setting name="cacheEnabled" value="false" /> <setting name="useGeneratedKeys" value="true" /> <setting name="defaultExecutorType" value="REUSE" /> </settings> <environments default="development"> <environment id="development"> <transactionManager type="jdbc" /> <dataSource type="POOLED"> <!-- <property name="driver" value="oracle.jdbc.driver.OracleDriver"/> <property name="url" value="jdbc:oracle:thin:@192.168.56.201:1521:system"/> --> <property name="driver" value="com.mysql.jdbc.Driver" /> <property name="url" value="jdbc:mysql://localhost:3306/mybatis" /> <property name="username" value="root" /> <property name="password" value="123456" /> </dataSource> </environment> </environments> <mappers> <mapper resource="com/hb/bean/classesMapper.xml" /> </mappers> </configuration>