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MyBatis动态sql与多表查询

2022-06-24 20:31:32 阅读：153 来源： 互联网

标签：mapper 多表 name public session sql MyBatis com id

一、MyBatis增删改查

（一）mapper接口映射

1．写接口

接口名与xml除去扩展名一样（推荐）
xml的namespace必须是UserMapper接口全限定名（包名+类名）

2．写mapper映射接口的方法遵循的原则

接口名与xml除去扩展名一样（推荐）
接口的方法名与xml的id一样
接口的方法的参数类型与xml的parameterType一样
接口的方法的返回值类型与xml的resultType一样(返回list接口方法的返回值类型是List元素类型)

<?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.tjetc.mapper.UserMapper">
    <select id="findById" parameterType="int" resultType="com.tjetc.domain.User">
      SELECT * FROM user where id=#{id}
  </select>
    <select id="findByUsername" parameterType="string" resultType="com.tjetc.domain.User">
      SELECT * FROM user where username=#{value}
  </select>
    <select id="findAll" resultType="User">
        SELECT * FROM user
    </select>
    <insert id="add" parameterType="user">
        insert  into user(username,password) values(#{username},#{password})
    </insert>
    <update id="update" parameterType="user">
        update user set username=#{username},password=#{password} where id=#{id}
    </update>
    <delete id="del" parameterType="int">
        delete  from  user where id=#{id}
    </delete>
</mapper>

package com.tjetc.mapper;
import com.tjetc.domain.User;
import java.util.List;
public interface UserMapper {
    User findById(int id);
    User findByUsername(String username);
    List<User> findAll();
    void add(User user);
    void update(User user);
    void del(int  id);
}

@Test
    public void testFind2() {
        try {
//        创建SqlSessionFactory
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsReader("mybatis.xml"));
//            得到session对象
            SqlSession session = sqlSessionFactory.openSession();
            //得到mapper接口的实现对象
            UserMapper mapper = session.getMapper(UserMapper.class);
//            通过session对象操作数据库
            User user = mapper.findById(1);
//            控制台打印user对象
            System.out.println(user);
//            关闭session
            session.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    @Test
    public void testFindByUsername2() {
        try {
//        创建SqlSessionFactory
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsReader("mybatis.xml"));
//            得到session对象
            SqlSession session = sqlSessionFactory.openSession();
            //得到mapper接口的实现对象
            UserMapper mapper = session.getMapper(UserMapper.class);
//            通过session对象操作数据库
            User user = mapper.findByUsername("admin");
//            控制台打印user对象
            System.out.println(user);
//            关闭session
            session.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    @Test
    public void testFindAll2() {
        try {
//        创建SqlSessionFactory
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsReader("mybatis.xml"));
//            得到session对象
            SqlSession session = sqlSessionFactory.openSession();
            //得到mapper接口的实现对象
            UserMapper mapper = session.getMapper(UserMapper.class);
//            通过session对象操作数据库
            List<User> list = mapper.findAll();
//            控制台打印list对象
            System.out.println(list);
//            关闭session
            session.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    @Test
    public void testAdd2() {
        try {
//        创建SqlSessionFactory
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsReader("mybatis.xml"));
//            得到session对象
            SqlSession session = sqlSessionFactory.openSession();
            //得到mapper接口的实现对象
            UserMapper mapper = session.getMapper(UserMapper.class);
//            通过session对象操作数据库
            User user = new User("zl", "123");
            mapper.add(user);
            //提交事务
            session.commit();
//            关闭session
            session.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    @Test
    public void testUpdate2() {
        try {
//        创建SqlSessionFactory
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsReader("mybatis.xml"));
//            得到session对象
            SqlSession session = sqlSessionFactory.openSession();
            //得到mapper接口的实现对象
            UserMapper mapper = session.getMapper(UserMapper.class);
//            通过session对象操作数据库
            User user = new User(8,"zl2", "123");
            mapper.update(user);
            //提交事务
            session.commit();
//            关闭session
            session.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    @Test
    public void testDel2() {
        try {
//        创建SqlSessionFactory
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsReader("mybatis.xml"));
//            得到session对象
            SqlSession session = sqlSessionFactory.openSession();
            //得到mapper接口的实现对象
            UserMapper mapper = session.getMapper(UserMapper.class);
//            通过session对象操作数据库
           mapper.del(8);
            //提交事务
            session.commit();
//            关闭session
            session.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

二、MyBatis中的动态SQL

（一）if 判断条件是否成立

<select id="findAll" parameterType="User" resultType="User">
    SELECT * FROM user where 1=1
    <if test="username!=null">
        and username=#{username}
    </if>
    <if test="password!=null">
        and password=#{password}
    </if>
</select>

@Test
    public void testFindAll2() {
        try {
//        创建SqlSessionFactory
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsReader("mybatis.xml"));
//            得到session对象
            SqlSession session = sqlSessionFactory.openSession();
            //得到mapper接口的实现对象
            UserMapper mapper = session.getMapper(UserMapper.class);
//            通过session对象操作数据库
            User user = new User();
            user.setUsername("admin");
            List<User> list = mapper.findAll(user);
//            控制台打印list对象
            System.out.println(list);
//            关闭session
            session.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

==> Preparing: SELECT * FROM user where 1=1 and username=?

==> Parameters: admin(String)

<== Columns: id, password, username

<== Row: 1, 123456, admin

<== Total: 1

[User{id=1, username='admin', password='123456'}]

（二）choose 相当于 if elseif else 只有一个when或者otherwise被执行

<select id="findAll" parameterType="User" resultType="User">
    SELECT * FROM user where 1=1
    <choose>
        <when test="username!=null">
            and username=#{username}
        </when>
        <when test="password!=null">
            and password=#{password}
        </when>
        <otherwise>
            and 2=2
        </otherwise>
    </choose>
</select>

==> Preparing: SELECT * FROM user where 1=1 and username=?

==> Parameters: admin(String)

<== Columns: id, password, username

<== Row: 1, 123456, admin

<== Total: 1

[User{id=1, username='admin', password='123456'}]

（三）where 增加where条件，如果没有条件成立，where不会出现在sql语句中，反之出现sql语句中，并且忽略where后面的第一个and或者or

<select id="findAll" parameterType="User" resultType="User">
    SELECT * FROM user
    <where>
        <if test="username!=null">
            and username=#{username}
        </if>
        <if test="password!=null">
            and password=#{password}
        </if>
    </where>
</select>

==> Preparing: SELECT * FROM user WHERE username=?

==> Parameters: admin(String)

<== Columns: id, password, username

<== Row: 1, 123456, admin

<== Total: 1

[User{id=1, username='admin', password='123456'}]

（四）trim 例如<trim prefix="where" prefixOverrides="and | or"> 忽略where后面的第一个and或者or

<select id="findAll" parameterType="User" resultType="User">
    SELECT * FROM user
    <trim prefix="where" prefixOverrides="and | or">
        <if test="username!=null">
            and username=#{username}
        </if>
        <if test="password!=null">
            and password=#{password}
        </if>
    </trim>
</select>

==> Preparing: SELECT * FROM user where username=?

==> Parameters: admin(String)

<== Columns: id, password, username

<== Row: 1, 123456, admin

<== Total: 1

[User{id=1, username='admin', password='123456'}]

（五）set 后面必须满足于一个条件，不然不满足sql语法

<update id="update" parameterType="user">
    update user
     <set>
         <if test="username!=null">
             username=#{username},
         </if>
         <if test="password!=null">
             password=#{password},
         </if>
     </set>
    where id=#{id}
</update>

 @Test
    public void testUpdate2() {
        try {
//        创建SqlSessionFactory
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsReader("mybatis.xml"));
//            得到session对象
            SqlSession session = sqlSessionFactory.openSession();
            //得到mapper接口的实现对象
            UserMapper mapper = session.getMapper(UserMapper.class);
//            通过session对象操作数据库
            User user = new User();
            user.setId(7);
            user.setUsername("liubei");
            mapper.update(user);
            //提交事务
            session.commit();
//            关闭session
            session.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

==> Preparing: update user SET username=? where id=?

==> Parameters: liubei(String), 7(Integer)

<== Updates: 1

（六）foreach

1．单参list

<select id="findAll2"  resultType="User">
    SELECT * FROM user where id in
    <foreach collection="list" item="item" open="(" close=")" separator=",">
        #{item}
    </foreach>
</select>

List<User> findAll2(List<Integer> list);

 @Test
    public void testFindAll22() {
        try {
//        创建SqlSessionFactory
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsReader("mybatis.xml"));
//            得到session对象
            SqlSession session = sqlSessionFactory.openSession();
            //得到mapper接口的实现对象
            UserMapper mapper = session.getMapper(UserMapper.class);
//            通过session对象数据库
            List<Integer> list1 = Arrays.asList(1, 3, 6);
            List<User> list = mapper.findAll2(list1);
//            控制台打印list对象
            System.out.println(list);
//            关闭session
            session.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

==> Preparing: SELECT * FROM user where id in ( ? , ? , ? )

==> Parameters: 1(Integer), 3(Integer), 6(Integer)

<== Columns: id, password, username

<== Row: 1, 123456, admin

<== Row: 3, 1111, admin1

<== Row: 6, 2333322, 3222

<== Total: 3

[User{id=1, username='admin', password='123456'}, User{id=3, username='admin1', password='1111'}, User{id=6, username='3222', password='2333322'}]

2．单参数组

<select id="findAll2"  resultType="User">
    SELECT * FROM user where id in
    <foreach collection="array" item="item" open="(" close=")" separator=",">
        #{item}
    </foreach>
</select>

List<User> findAll2(Integer[] array);

@Test
    public void testFindAll22() {
        try {
//        创建SqlSessionFactory
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsReader("mybatis.xml"));
//            得到session对象
            SqlSession session = sqlSessionFactory.openSession();
            //得到mapper接口的实现对象
            UserMapper mapper = session.getMapper(UserMapper.class);
//            通过session对象数据库
            Integer[] array=new Integer[]{1,3,6};
            List<User> list = mapper.findAll2(array);
//            控制台打印list对象
            System.out.println(list);
//            关闭session
            session.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

==> Preparing: SELECT * FROM user where id in ( ? , ? , ? )

==> Parameters: 1(Integer), 3(Integer), 6(Integer)

<== Columns: id, password, username

<== Row: 1, 123456, admin

<== Row: 3, 1111, admin1

<== Row: 6, 2333322, 3222

<== Total: 3

[User{id=1, username='admin', password='123456'}, User{id=3, username='admin1', password='1111'}, User{id=6, username='3222', password='2333322'}]

3．多个参数使用map

<select id="findAll2"  resultType="User">
    SELECT * FROM user where username like concat('%',#{username},'%')  and id in
    <foreach collection="ids" item="item" open="(" close=")" separator=",">
        #{item}
    </foreach>
</select>

List<User> findAll2(Map<String,Object> map);

@Test
    public void testFindAll22() {
        try {
//        创建SqlSessionFactory
            SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsReader("mybatis.xml"));
//            得到session对象
            SqlSession session = sqlSessionFactory.openSession();
            //得到mapper接口的实现对象
            UserMapper mapper = session.getMapper(UserMapper.class);
//            通过session对象数据库
            Map<String,Object> map=new HashMap<>();
            map.put("username", "d");
            map.put("ids", Arrays.asList(1,3,6));
            List<User> list = mapper.findAll2(map);
//            控制台打印list对象
            System.out.println(list);
//            关闭session
            session.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

==> Preparing: SELECT * FROM user where username like '%d%' and id in ( ? , ? , ? )

==> Parameters: 1(Integer), 3(Integer), 6(Integer)

<== Columns: id, password, username

<== Row: 1, 123456, admin

<== Row: 3, 1111, admin1

<== Total: 2

[User{id=1, username='admin', password='123456'}, User{id=3, username='admin1', password='1111'}]

三、Mybatis多表查询

（一）一对一

一个对一个,人和身份证属于一对一,一个类只有一个另个类的引用

1．建立数据库表

CREATE TABLE `person` (

`id` int(11) NOT NULL AUTO_INCREMENT,

`name` varchar(255) DEFAULT NULL,

PRIMARY KEY (`id`)

)

CREATE TABLE `idcard` (

`id` int(11) NOT NULL AUTO_INCREMENT,

`code` varchar(255) DEFAULT NULL,

`pid` int(11) DEFAULT NULL,

PRIMARY KEY (`id`)

)

2．实体类

package com.tjetc.entity;

public class Person {
    private int id;
    private String name;
    private IdCard idCard;

    public IdCard getIdCard() {
        return idCard;
    }

    public void setIdCard(IdCard idCard) {
        this.idCard = idCard;
    }

    public Person(String name) {
        this.name = name;
    }

    public Person() {
    }

    public Person(int id, String name) {
        this.id = id;
        this.name = name;
    }

    @Override
    public String toString() {
        return "Person{" +
                "id=" + id +
                ", 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;
    }
}

package com.tjetc.entity;

public class IdCard {
    private int id;
    private String code;
    private Person person;

    @Override
    public String toString() {
        return "IdCard{" +
                "id=" + id +
                ", code='" + code + '\'' +
                '}';
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getCode() {
        return code;
    }

    public void setCode(String code) {
        this.code = code;
    }

    public Person getPerson() {
        return person;
    }

    public void setPerson(Person person) {
        this.person = person;
    }
}

3．建立映射文件和映射接口

PersonMapper.xml: <?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.tjetc.mapper.PersonMapper">
   <insert id="add" parameterType="person" useGeneratedKeys="true" keyProperty="id">
       insert into person(name) values(#{name})
   </insert>
</mapper>

package com.tjetc.mapper;

import com.tjetc.entity.Person;

public interface PersonMapper {
void add(Person person);
}

IdCardMapper.xml:

package com.tjetc.mapper;

import com.tjetc.entity.IdCard;

public interface IdCardMapper {
void add(IdCard idCard);
}

4．mybatis.xml

<package name="com.tjetc.mapper"/>扫描指定包下的所有mapper配置文件，可以解决减少配置mapper映射文件数量

<mappers>
        <package name="com.tjetc.mapper"/>

    </mappers>

5．测试方法

@Test
    public void testAdd() {
//        创建SqlSessionFactory
        SqlSessionFactory sqlSessionFactory = null;
        try {
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsReader("mybatis.xml"));
//            得到session对象
            SqlSession session = sqlSessionFactory.openSession();
            //得到mapper
            PersonMapper personMapper = session.getMapper(PersonMapper.class);
                     //向数据库person表添加一条记录
            Person person = new Person("张三");
            personMapper.add(person);
            System.out.println(person);
            //创建idCard对象
            IdCard idCard = new IdCard();
            idCard.setCode("12345678234567");
            idCard.setPerson(person);
            //插入数据库
            IdCardMapper cardMapper = session.getMapper(IdCardMapper.class);
            cardMapper.add(idCard);

            session.commit();
            session.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

6．运行效果

==> Preparing: insert into person(name) values(?)

==> Parameters: 张三(String)

<== Updates: 1

Person{id=1, name='张三'}

==> Preparing: insert into idcard(code,pid) values (?,?)

==> Parameters: 12345678234567(String), 1(Integer)

<== Updates: 1

7．课堂练习

使用mybatis实现person和idcard表一对一的插入数据库表

8．resultMap

resultMap:结果映射,查询结果列与实体类对象的属性之间进行映射,还能进行关联的映射.

9．一对一的关联嵌套select

PersonMapper.xml:

<?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.tjetc.mapper.PersonMapper">
   <insert id="add" parameterType="com.tjetc.entity.Person" useGeneratedKeys="true" keyProperty="id">
       insert into person(name) values(#{name})
   </insert>
    <select id="findById" parameterType="int" resultMap="personMap">
        select * from person where id=#{id}
    </select>
    <resultMap id="personMap" type="com.tjetc.entity.Person">
        <id column="id" property="id"></id>
        <result column="name" property="name"></result>
        <association property="idCard" column="id" select="findByPid"></association>
    </resultMap>
    <select id="findByPid" parameterType="int" resultType="com.tjetc.entity.IdCard">
        select * from idcard where pid=#{id}
    </select>
</mapper>

public interface PersonMapper {
void add(Person person);
Person findById(int id);
}

@Test
    public void testFindById() {
//        创建SqlSessionFactory
        SqlSessionFactory sqlSessionFactory = null;
        try {
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsReader("mybatis.xml"));
//            得到session对象
            SqlSession session = sqlSessionFactory.openSession();
            //得到mapper
            PersonMapper personMapper = session.getMapper(PersonMapper.class);
            //调用PersonMapper的方法
            Person person = personMapper.findById(1);
            System.out.println(person);
            IdCard idCard = person.getIdCard();
            System.out.println(idCard);
            session.close();
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

==> Preparing: select * from person where id=?

==> Parameters: 1(Integer)

<== Columns: id, name

<== Row: 1, 张三

====> Preparing: select * from idcard where pid=?

====> Parameters: 1(Integer)

<==== Columns: id, code, pid

<==== Row: 1, 12345678234567, 1

<==== Total: 1

<== Total: 1

Person{id=1, name='张三'}

IdCard{id=1, code='12345678234567'}

10．课堂练习

一对一的关联嵌套select

11．一对一的关联嵌套resultMap

<select id="findById" parameterType="int" resultMap="personMap">
   select p.id,p.name,c.id cid,c.code from person p inner join idcard c on p.id=c.pid where p.id=#{id}
</select>
<resultMap id="personMap" type="com.tjetc.entity.Person">
    <id column="id" property="id"></id>
    <result column="name" property="name"></result>
    <association property="idCard" resultMap="cardMap"></association>
</resultMap>
<resultMap id="cardMap" type="IdCard">
    <id column="cid" property="id"></id>
    <result column="code" property="code"></result>
</resultMap>

==> Preparing: select p.*,c.id cid,c.code from person p,idcard c where p.id=c.pid and p.id=?

==> Parameters: 1(Integer)

<== Columns: id, name, cid, code

<== Row: 1, 张三, 1, 12345678234567

<== Total: 1

Person{id=1, name='张三'}

IdCard{id=1, code='12345678234567'}

（二）一对多

1．建表

myclass

student

CREATE TABLE `myclass` (

`id` int(11) NOT NULL AUTO_INCREMENT,

`name` varchar(255) DEFAULT NULL,

PRIMARY KEY (`id`)

)

CREATE TABLE `student` (

`id` int(11) NOT NULL AUTO_INCREMENT,

`name` varchar(255) DEFAULT NULL,

`cid` int(11) DEFAULT NULL,

PRIMARY KEY (`id`)

)

2．实体类

package com.tjetc.domain;

import java.util.ArrayList;
import java.util.List;

public class MyClass {
    private int id;
    private String name;
    private List<Student> students=new ArrayList<>();

    public List<Student> getStudents() {
        return students;
    }

    public void setStudents(List<Student> students) {
        this.students = students;
    }

    public MyClass(String name) {
        this.name = name;
    }

    public MyClass(int id, String name) {
        this.id = id;
        this.name = name;
    }

    public MyClass() {
    }

    @Override
    public String toString() {
        return "MyClass{" +
                "id=" + id +
                ", 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;
    }
}

package com.tjetc.entity;

public class Student {
    private int id;
    private String name;
    private MyClass myClass;

    public Student(String name) {
        this.name = name;
    }

    public Student() {
    }

    @Override
    public String toString() {
        return "Student{" +
                "id=" + id +
                ", 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;
    }

    public MyClass getMyClass() {
        return myClass;
    }

    public void setMyClass(MyClass myClass) {
        this.myClass = myClass;
    }
}

3．映射文件和映射接口

MyClassMapper.xml:

package com.tjetc.mapper;

import com.tjetc.entity.MyClass;

public interface MyClassMapper {
void add(MyClass myClass);
}

StudentMapper.xml: <?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.tjetc.mapper.StudentMapper">
<insert id="add" parameterType="Student">
insert into student(name,cid) values (#{name},#{myClass.id});
</insert>
</mapper>

package com.tjetc.mapper;

import com.tjetc.entity.Student;

public interface StudentMapper {
void add(Student student);
}

@Test
    public void testAdd(){
        try {
            SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsReader("mybatis.xml"));
            SqlSession session = factory.openSession();
            MyClassMapper myClassMapper = session.getMapper(MyClassMapper.class);
            StudentMapper studentMapper = session.getMapper(StudentMapper.class);
            MyClass myClass = new MyClass("1班");
            myClassMapper.add(myClass);

//            创建3个学生
            Student student1 = new Student("zs");
            Student student2 = new Student("ls");
            Student student3 = new Student("zl");
//            设置班级
            student1.setMyClass(myClass);
            student2.setMyClass(myClass);
            student3.setMyClass(myClass);

//            保存学生
            studentMapper.add(student1);
            studentMapper.add(student2);
            studentMapper.add(student3);
//            提交事务
            session.commit();
//            close
            session.close();

        } catch (IOException e) {
            e.printStackTrace();
        }
    }

==> Preparing: insert into myclass(name) values(?)

==> Parameters: 1班(String)

<== Updates: 1

==> Preparing: insert into student(name,cid) values (?,?);

==> Parameters: zs(String), 1(Integer)

<== Updates: 1

==> Preparing: insert into student(name,cid) values (?,?);

==> Parameters: ls(String), 1(Integer)

<== Updates: 1

==> Preparing: insert into student(name,cid) values (?,?);

==> Parameters: zl(String), 1(Integer)

<== Updates: 1

4．一对多的集合嵌套select collection

MyClassMapper.xml:

<select id="findById" parameterType="int" resultMap="classMap">
    select * from myclass where id=#{id}
</select>
<resultMap id="classMap" type="MyClass">
    <id column="id" property="id"></id>
    <result column="name" property="name"></result>
    <collection property="students" ofType="Student" column="id" select="findByCid"></collection>
</resultMap>
<select id="findByCid" parameterType="int" resultType="Student">
    select * from student where cid=#{id}
</select>

MyClass findById(int id);

@Test
public void testFind() {
    try {
        SqlSessionFactory factory = new SqlSessionFactoryBuilder().build(Resources.getResourceAsReader("mybatis.xml"));
        SqlSession session = factory.openSession();
        MyClassMapper myClassMapper = session.getMapper(MyClassMapper.class);
        MyClass myClass = myClassMapper.findById(1);
        System.out.println(myClass);
        List<Student> students = myClass.getStudents();
        for (Student student : students) {
            System.out.println(student);
        }
        session.close();
    } catch (IOException e) {
        e.printStackTrace();
    }
}

==> Preparing: select * from myclass where id=?

==> Parameters: 1(Integer)

<== Columns: id, name

<== Row: 1, 1班

<== Total: 1

==> Preparing: select * from student where cid=?

==> Parameters: 1(Integer)

<== Columns: id, name, cid

<== Row: 1, zs, 1

<== Row: 2, ls, 1

<== Row: 3, zl, 1

<== Total: 3

MyClass{id=1, name='1班'}

Student{id=1, name='zs'}

Student{id=2, name='ls'}

Student{id=3, name='zl'}

5．一对多的集合嵌套resultMap collection

<select id="findById" parameterType="int" resultMap="classMap">
    SELECT c.*,s.id sid,s.name sname FROM myclass c,student s where c.id=s.cid and c.id=#{id}
</select>
<resultMap id="classMap" type="MyClass">
    <id column="id" property="id"></id>
    <result column="name" property="name"></result>
    <collection property="students" ofType="Student" resultMap="studentMap"></collection>
</resultMap>
<resultMap id="studentMap" type="Student">
    <id column="sid" property="id"></id>
    <result column="sname" property="name"></result>
</resultMap>

==> Preparing: SELECT c.*,s.id sid,s.name sname FROM myclass c,student s where c.id=s.cid and c.id=?

==> Parameters: 1(Integer)

<== Columns: id, name, sid, sname

<== Row: 1, 1班, 1, zs

<== Row: 1, 1班, 2, ls

<== Row: 1, 1班, 3, zl

<== Total: 3

MyClass{id=1, name='1班'}

Student{id=1, name='zs'}

Student{id=2, name='ls'}

Student{id=3, name='zl'}

（三）多对多

1．建表

学生选课

CREATE TABLE `teacher` (

`id` int(11) NOT NULL AUTO_INCREMENT,

`name` varchar(255) DEFAULT NULL,

PRIMARY KEY (`id`)

)

CREATE TABLE `course` (

`id` int(11) NOT NULL AUTO_INCREMENT,

`name` varchar(255) DEFAULT NULL,

PRIMARY KEY (`id`)

)

CREATE TABLE `sc` (

`tid` int(11) NOT NULL,

`cid` int(11) DEFAULT NULL

)

2．实体类

package com.tjetc.entity;

import java.util.ArrayList;
import java.util.List;

public class Teacher {
    private int id;
    private String name;
    private List<Course> courses = new ArrayList<>();

    public List<Course> getCourses() {
        return courses;
    }

    public void setCourses(List<Course> courses) {
        this.courses = courses;
    }

    public Teacher() {
    }

    public Teacher(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "Teacher{" +
                "id=" + id +
                ", 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;
    }
}

package com.tjetc.entity;

import java.util.ArrayList;
import java.util.List;

public class Course {
    private int id;
    private String name;
    private List<Teacher> teachers =new ArrayList<>();

    public List<Teacher> getTeachers() {
        return teachers;
    }

    public void setTeachers(List<Teacher> teachers) {
        this.teachers = teachers;
    }

    public Course() {
    }

    public Course(String name) {
        this.name = name;
    }

    @Override
    public String toString() {
        return "Course{" +
                "id=" + id +
                ", 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;
    }
}

3．映射文件和接口

TeacherMapper.xml:

</mapper>

package com.tjetc.mapper;

import com.tjetc.entity.Teacher;
import org.apache.ibatis.annotations.Param;

public interface TeacherMapper {
    void add(Teacher teacher);

    /**
     * 添加sc表
     *
     * @param t_id tid
     * @param c_id cid
     */
    void addSc(@Param("tid") int t_id, @Param("cid") int c_id);
}

CourseMapper.xml:

public interface CourseMapper {
void add(Course course);
}

package com.tjetc;

import com.tjetc.common.SqlSessionFactoryUtil;
import com.tjetc.domain.Course;
import com.tjetc.domain.Teacher;
import com.tjetc.mapper.CourseMapper;
import com.tjetc.mapper.TeacherMapper;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;

public class TeacherAndCourseTest {
    @Test
    public void add() {
        SqlSession sqlSession = SqlSessionFactoryUtil.getSqlSession("mybatis.xml");
        TeacherMapper teacherMapper = sqlSession.getMapper(TeacherMapper.class);
        CourseMapper courseMapper = sqlSession.getMapper(CourseMapper.class);

        //new三门课程
        Course course1 = new Course("java");
        Course course2 = new Course("JSP");
        Course course3 = new Course("Mybatis");
        //三门课程添加到数据库
        courseMapper.add(course1);
        courseMapper.add(course2);
        courseMapper.add(course3);

        //new 三个老师
        Teacher teacher1 = new Teacher("zs");
        Teacher teacher2 = new Teacher("ls");
        Teacher teacher3 = new Teacher("zl");
      //三个老师添加到数据库
        teacherMapper.add(teacher1);
        teacherMapper.add(teacher2);
        teacherMapper.add(teacher3);

        //zs老师选3门课程
        teacherMapper.addSc(teacher1.getId(),course1.getId());
        teacherMapper.addSc(teacher1.getId(),course2.getId());
        teacherMapper.addSc(teacher1.getId(),course3.getId());

        //ls老师选1和2课程
        teacherMapper.addSc(teacher2.getId(),course1.getId());
        teacherMapper.addSc(teacher2.getId(),course2.getId());

        //zs老师选2和3课程
        teacherMapper.addSc(teacher3.getId(),course2.getId());
        teacherMapper.addSc(teacher3.getId(),course3.getId());

        sqlSession.commit();

        sqlSession.close();
    }
}

==> Preparing: insert into course (name) values (?)

==> Parameters: Java(String)

<== Updates: 1

==> Preparing: insert into course (name) values (?)

==> Parameters: JSP(String)

<== Updates: 1

==> Preparing: insert into course (name) values (?)

==> Parameters: MyBatis(String)

<== Updates: 1

==> Preparing: insert into student (name) values (?)

==> Parameters: zs(String)

<== Updates: 1

==> Preparing: insert into student (name) values (?)

==> Parameters: ls(String)

<== Updates: 1

==> Preparing: insert into student (name) values (?)

==> Parameters: zl(String)

<== Updates: 1