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5.1一对一关联查询

5.1.1创建表和数据

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) REFERENCESteacher(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);

5.1.2定义两个实体类

Classes.java

package com.entity;public class Classes {
       private int id;    private String name;    private Teacher teacher;    public Classes()    {    }    public Classes(int id, String name, Teacher teacher) {        super();        this.id = id;        this.name = name;        this.teacher = teacher;    }    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;    }    @Override    public String toString() {        return "Classes [id=" + id + ", name=" + name + ", teacher=" + teacher                + "]";    }}

Teacher.java

package com.entity;public class Teacher {
       private int id;    private String name;    public Teacher()    {    }    public Teacher(int id, String name) {        super();        this.id = id;        this.name = 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 + "]";    }}

5.1.3定义映射文件

ClassesMapper.xml

   
       
        
        
            select * from class c,teacher t where c.teacher_id=t.t_id and c.c_id=#{id};        
            
             
             
                 
                  
              
         
        
        
            SELECT * FROM class WHERE c_id=#{id};        
            SELECT t_id id,t_name name FROM teacher WHERE t_id=#{id}        
            
             
             
                 
                  
              
         
    
   

• association：用于一对一的关联查询
• property：对象属性名称
• javaType：对象属性的类型
• column：所对应的外键字段名称
• select：使用另一个查询封装的结构

5.1.4config.xml中注册ClassMapper.xml

5.1.5测试类

package com.test;import java.io.IOException;import org.apache.ibatis.session.SqlSession;import org.junit.Test;import com.entity.Classes;import com.util.MybatisUtil;public class Test4 {    //第一种方式的测试    @Test    public void getClass1() throws IOException    {        SqlSession session=MybatisUtil.getSession();        String statement="com.config.ClassMapper.getClass";        Classes classes=session.selectOne(statement, 1);        session.close();        System.out.println(classes);    }    //第二种方式的测试        @Test        public void getClass2() throws IOException        {            SqlSession session=MybatisUtil.getSession();            String statement="com.config.ClassMapper.getClass2";            Classes classes=session.selectOne(statement, 1);            session.close();            System.out.println(classes);        }}

5.2一对多关联表查询

5.2.1创建表和数据

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);

5.2.2定义实体类

Classes.java

package com.entity;import java.util.List;public class Classes {
       private int id;    private String name;    private Teacher teacher;    private List
   
     list;    public Classes() {    }    public Classes(int id, String name, Teacher teacher, List
    
      list) {        super();        this.id = id;        this.name = name;        this.teacher = teacher;        this.list = list;    }    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;    }    @Override    public String toString() {        return "Classes [id=" + id + ", name=" + name + ", teacher=" + teacher                + ", list=" + list + "]";    }}
    
   

5.2.3定义 sql 映射文件 Class2Mapper.xml

Class2Mapper.xml

   
       
        
        
            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 * FROM class WHERE c_id=#{id};          
             SELECT t_id id,t_name name FROM teacher WHERE t_id=#{id}          
             SELECT s_id id,s_name name FROM student WHERE class_id=#{id}          
            
             
             
             
             
             
         
    
   

• collection：做一对多关联映射查询
• ofType：指点集合中元素对象类型

5.2.4将映射文件注册到config.xml中

config.xml

5.2.5测试类

Test5.java

package com.test;import java.io.IOException;import org.apache.ibatis.session.SqlSession;import org.junit.Test;import com.entity.Classes;import com.util.MybatisUtil;public class Test5 {    //方式一    @Test    public void testSelect1() throws IOException    {        SqlSession session=MybatisUtil.getSession();        String statement="com.config.Class2Mapper.getClass";        Classes classes=session.selectOne(statement, 1);        session.close();        System.out.println(classes);    }    //方式二        @Test        public void testSelect2() throws IOException        {            SqlSession session=MybatisUtil.getSession();            String statement="com.config.Class2Mapper.getClass2";            Classes classes=session.selectOne(statement, 1);            session.close();            System.out.println(classes);        }}

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