Mybatis简单上手

一、搭建MySQL环境

• 创建maven项目

• 导入maven依赖

    
        mysql
        mysql-connector-java
        5.1.47
    

    
        org.mybatis
        mybatis
        3.5.2
    

    
        junit
        junit
        4.12
    

• 配置xml和properties文件的扫描方式

    
        
            
            
                src/main/resources
                
                    **/*.properties
                    **/*.xml
                
                true
            

            
            
                src/main/java
                
                    **/*.properties
                    **/*.xml
                
                true
            
        
    

• 完整pom.xml

    4.0.0

    com.yaco
    mybatis
    pom
    1.0-SNAPSHOT
    
        mybatis01
        mybatis02
        mybatis03
    

    
        
            mysql
            mysql-connector-java
            5.1.47
        

        
            org.mybatis
            mybatis
            3.5.2
        

        
            junit
            junit
            4.12
        
    
    
    
        
            
            
                src/main/resources
                
                    **/*.properties
                    **/*.xml
                
                true
            

            
            
                src/main/java
                
                    **/*.properties
                    **/*.xml
                
                true
            
        
    

二、实现简单的增删改查

1、创建数据库

创建一个简单的用户表，表中含有三个属性，用户id，用户名和用户密码

CREATE DATABASE mybatis;
USE mybatis;

# 创建表
CREATE TABLE `user`(
    `id` INT(20) NOT NULL AUTO_INCREMENT PRIMARY KEY,
    `name` VARCHAR(30) DEFAULT NULL,
    `pwd` VARCHAR(30) DEFAULT NULL
)ENGINE=INNODB DEFAULT CHARSET=utf8;

# 插入数据
INSERT INTO `user`(`id`,`name`,`pwd`) VALUES
(1,'张三','123456'),
(2,'李四','123456'),
(3,'狂神','123456')

2、创建mybatis-config.xml配置文件

主要配置数据连接的相关信息，包括驱动器、url、连接数据库的用户名和密码、是否启动数据库连接池等信息

使用mapper配置userMapper.xml的映射文件位置

3、创建对应的数据库中的实体类

实体类对应数据库中User表中的字符名，此处与表中字段名完全一致，也可以不一致

public class User {

    private int id;
    private String name;
    private String pwd;

    public User() {
    }

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

    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 String getPwd() {
        return pwd;
    }

    public void setPwd(String pwd) {
        this.pwd = pwd;
    }

    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", pwd='" + pwd + '\'' +
                '}';
    }
}

创建UserMapper的持久层接口

public interface UserMapper {

    // 查
    List getUserList();

    // 增
    int addUser(User user);

    // 删
    void deleteById(int id);

    // 该
    int update(User user);

    // 查找一个
    User findById(int id);

    // 根据用户名和密码查询，使用map
    User findByNameAnsPwd(Map map);

    // 模糊查询
    List findUserLike(String value);
}

4、创建mapper映射文件

    
        update user set name=#{name}, pwd=#{pwd}  where id = #{id}
    

    
        delete from user where id = #{id}
    

    
        select * from user
    

    
        select * from user where id = #{id}
    

    
        select * from user where name=#{name} and pwd=#{pwd}
    

    
        select * from user where name like #{value}
    

    
        insert into user (id, name, pwd) values (#{id},#{name},#{pwd})
    

5、创建一个MybatisUtil工具类

MybatisUtil工具类用于获取执行映射文件中的sql语句的SqlSession

public class MybatisUtil {

    private static SqlSessionFactory sqlSessionFactory;

    static {
        // 获取SqlSessionFactory对象
        try {
            String resource = "mybatis-config.xml";
            InputStream inputStream = Resources.getResourceAsStream(resource);
            sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static SqlSession getSqlSession() {
        return sqlSessionFactory.openSession();
    }
}

6、测试类

在test文件下做测试，保证包名与所测试的类包结构一致

public class UserDaoTest {

    @Test
    public void testList() {
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        UserMapper userDao = sqlSession.getMapper(UserMapper.class);
        List userList = userDao.getUserList();
        for (User user : userList) {
            System.out.println(user);
        }
        sqlSession.close();
    }

    @Test
    public void testFindOne() {
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        UserMapper userDao = sqlSession.getMapper(UserMapper.class);
        User user = userDao.findById(1);
        System.out.println(user);
        sqlSession.close();
    }

    @Test
    public void testInsert() {
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        UserMapper userDao = sqlSession.getMapper(UserMapper.class);
        User user = new User();
        user.setId(5);
        user.setName("hj");
        user.setPwd("123456");
        int res = userDao.addUser(user);
        if(res > 0) {
            System.out.println("插入成工");
        }
        System.out.println(user);
        // 插入要提交事务
        sqlSession.commit();
        sqlSession.close();
    }

    @Test
    public void testUpdate() {
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        UserMapper userDao = sqlSession.getMapper(UserMapper.class);
        User user = new User();
        user.setId(5);
        user.setName("yaco");
        user.setPwd("123456");
        int res = userDao.update(user);
        if(res > 0) {
            System.out.println("更新成功");
        }
        System.out.println(user);
        // 插入要提交事务
        sqlSession.commit();
        sqlSession.close();
    }

    @Test
    public void testDelete() {
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        UserMapper userDao = sqlSession.getMapper(UserMapper.class);
        userDao.deleteById(5);
        sqlSession.commit();
        sqlSession.close();
    }

    @Test
    public void testMap() {
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        UserMapper userDao = sqlSession.getMapper(UserMapper.class);
        Map map = new HashMap();
        map.put("name", "张三");
        map.put("pwd","123456");
        User user = userDao.findByNameAnsPwd(map);
        System.out.println(user);
        sqlSession.close();
    }

    @Test
    public void testLike() {
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        UserMapper userDao = sqlSession.getMapper(UserMapper.class);
        List users = userDao.findUserLike("%李%");
        for (User user : users) {
            System.out.println(user);
        }
        sqlSession.close();
    }
}

三、使用Mybatis实现多对一查询

1、搭建数据表结构

创建两张表，分别式学生表和老师表，一个学生对应一个老师，一个老师可以对应多名学生。

CREATE TABLE student(
    id INT(20) NOT NULL AUTO_INCREMENT PRIMARY KEY,
    NAME VARCHAR(30) DEFAULT NULL
    tid INT(20) DEFAULT NULL,
    CONSTRAINT FOREIGN KEY(tid) REFERENCES teacher(id)
)ENGINE = INNODB DEFAULT CHARSET utf8

CREATE TABLE teacher(
    id INT(20) NOT NULL AUTO_INCREMENT PRIMARY KEY,
    NAME VARCHAR(20),
)ENGINE = INNODB DEFAULT CHARSET utf8

添加一些数据

2、搭建实体类及映射环境

• 实体类

public class Student {

    private int id;
    private String name;
    private 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 "Student{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", teacher=" + teacher +
                '}';
    }
}

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 + '\'' +
                '}';
    }
}

• StudentMapper持久层接口，查询学生，实现多对一的功能

public interface StudentMapper {

    List selectStudentList();

    List selectStudentList2();

    Teacher selectTeacherById(int id);
}

3、使用嵌套查询完成多对一查询

    
    
        
        
        
            
            
        
    

    
        select s.id as sid, s.name as sname, t.id as tid, t.name as tname from student s, teacher t where s.tid = t.id
    

4、使用子查询完成多对一查询

    
    
        
        
        
    

    
        select * from student
    

    
        select * from teacher where id = #{id};
    

5、测试

public class MybatisTest {

    @Test
    public void test() {
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
        List students = mapper.selectStudentList();
        for (Student student : students) {
            System.out.println(student);
        }
        sqlSession.close();
    }

    @Test
    public void test2() {
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        StudentMapper mapper = sqlSession.getMapper(StudentMapper.class);
        List students = mapper.selectStudentList2();
        for (Student student : students) {
            System.out.println(student);
        }
        sqlSession.close();
    }
}

测试输出

// 嵌套查询结果
Student{id=1, name='小明', teacher=Teacher{id=1, name='数学老师'}}
Student{id=2, name='小红', teacher=Teacher{id=2, name='语文老师'}}
Student{id=3, name='小兰', teacher=Teacher{id=3, name='英语老师'}}
Student{id=4, name='小宋', teacher=Teacher{id=1, name='数学老师'}}
Student{id=5, name='小丽', teacher=Teacher{id=2, name='语文老师'}}
Student{id=6, name='小叮', teacher=Teacher{id=3, name='英语老师'}}

// 子查询结果
Student{id=1, name='小明', teacher=Teacher{id=1, name='数学老师'}}
Student{id=2, name='小红', teacher=Teacher{id=2, name='语文老师'}}
Student{id=3, name='小兰', teacher=Teacher{id=3, name='英语老师'}}
Student{id=4, name='小宋', teacher=Teacher{id=1, name='数学老师'}}
Student{id=5, name='小丽', teacher=Teacher{id=2, name='语文老师'}}
Student{id=6, name='小叮', teacher=Teacher{id=3, name='英语老师'}}

四、使用Mybatis实现一对多查询

1、搭建实体类及映射环境

在上面多对一的情况下，学生实体类中有一个对应得老师实体引用，一对多得情况，老师实体类也要有一个学生得引用，因为是一对多得关系，这里用List存放学生集合

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 + '\'' +
                '}';
    }
}

public class Teacher {

    private int id;
    private String name;
    List 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 List getStudents() {
        return students;
    }

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

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

• 创建持久层TeacherMapper接口

public interface TeacherMapper {

    List selectTeacherById(@Param("tid") int tid);
}

2、使用嵌套查询完成一对多查询

    

        
            select t.id tid,t.name tname,s.id sid,s.name sname
            from student s,teacher t
            where s.tid = t.id and t.id = #{tid};
        

    
        
        
        
            
            
        
    

3、测试

public class MybatisTest {

    @Test
    public void test() {
        SqlSession sqlSession = MybatisUtil.getSqlSession();
        TeacherMapper mapper = sqlSession.getMapper(TeacherMapper.class);
        List teachers = mapper.selectTeacherById(1);
        for (Teacher teacher : teachers) {
            System.out.println(teacher);
        }
    }
}

用例输出

Teacher{id=1, name='数学老师', students=[Student{id=1, name='小明'}, Student{id=4, name='小宋'}]}