目录

使用注解开发

设置事务自动提交

mybatis运行原理

注解CRUD

lombok使用（偷懒神器，大神都不建议使用）

复杂查询环境（多对一）

复杂查询环境（一对多）

动态sql环境搭建

动态sql常用标签

    

---

使用注解开发

注解本质是反射机制，使用注解可以使得代码内容得到简化，注解可以取代注册文件UUserMapper.xml

如下面定义接口，在接口上方定义注解写sql语句

public interface UserMapper {
    @Select("select * from user")
    List<User> getUsers();
}

需要在核心配置文件绑定接口

设置事务自动提交

基于源码

 

我们可以设置事务自动提交

SqlSession  sqlSession=sqlSessionFactory.openSession(true);

mybatis运行原理

 

注解CRUD

查询所有用户

接口

@Select("select * from user")
List<User> getUsers();

测试

@Test
public void getUsers(){
    SqlSession sqlSession= MybatisUtils.getSqlSession();
    UserMapper mapper=sqlSession.getMapper(UserMapper.class);
    List<User> users=mapper.getUsers();
    for(User user:users){
        System.out.println(user);
    }
    sqlSession.close();
}

根据id查询用户

接口

@Select("select * from user where id=#{35342}")
    User getUserById(@Param("35342") int id);

测试

public void getUsers(){
    SqlSession sqlSession= MybatisUtils.getSqlSession();
    UserMapper mapper=sqlSession.getMapper(UserMapper.class);

    User userById=mapper.getUserById(1);
    System.out.println(userById);
    sqlSession.close();
}

增加用户

接口

@Insert("insert into user(id,name,pwd) values(#{id},#{name},#{pwd})")
    int addUser(User user);

测试

SqlSession sqlSession= MybatisUtils.getSqlSession();
UserMapper mapper=sqlSession.getMapper(UserMapper.class);
mapper.addUser(new User(12,"hello","Ssdd"));

修改用户信息

接口

@Update("UPDATE USER set NAME=#{name},PWD=#{pwd} where id=#{id}")
int updateUser(User user);

测试

SqlSession sqlSession= MybatisUtils.getSqlSession();
UserMapper mapper=sqlSession.getMapper(UserMapper.class);
mapper.updateUser(new User(12,"ttt","12443"));

删除用户

接口

@Delete("delete from user where id=#{id}")
int delUser(int id);

测试

SqlSession sqlSession= MybatisUtils.getSqlSession();
UserMapper mapper=sqlSession.getMapper(UserMapper.class);
mapper.delUser(12);

接口总的代码：

package com.dao;

import com.pojo.User;
import org.apache.ibatis.annotations.*;

import java.util.List;
import java.util.Map;

public interface UserMapper { 
    @Select("select * from user")
    List<User> getUsers();
//    通过id查询
@Select("select * from user where id=#{35342}")
    User getUserById(@Param("35342") int id);
@Insert("insert into user(id,name,pwd) values(#{id},#{name},#{pwd})")
    int addUser(User user);
@Update("UPDATE USER set NAME=#{name},PWD=#{pwd} where id=#{id}")
int updateUser(User user);
@Delete("delete from user where id=#{id}")
int delUser(int id);
}

测试总的代码：

import com.dao.UserMapper;
import com.pojo.User;
import com.utils.MybatisUtils;
import org.apache.ibatis.session.SqlSession;
import org.junit.Test;
import java.util.List;
public class test {
    @Test
    public void getUsers(){
        SqlSession sqlSession= MybatisUtils.getSqlSession();
        UserMapper mapper=sqlSession.getMapper(UserMapper.class);
        List<User> users=mapper.getUsers();
        for(User user:users){
            System.out.println(user);
        }
        User userById=mapper.getUserById(1);
        System.out.println(userById);
        mapper.updateUser(new User(12,"ttt","12443"));
        mapper.addUser(new User(12,"hello","Ssdd"));
        mapper.delUser(12);
        sqlSession.close();
    }
}

关于@Params()注解：

有多个参数则所有参数前一定要加上@Params()

lombok使用（偷懒神器，大神都不建议使用）

自动帮我们优化一些变量，但是会淡化我们对源码的理解

使用：导入jar包，在实体类上方加注解即可

@Data取代getter和setter方法

@AllArgsConstructor生成所有有参构造

@NoArgsConstructor生成所有无参构造

@ToString

如可以帮助我们写get，set,toString方法等

 

复杂查询环境（多对一）

实体类准备

//多对一
@Data
@ToString
public class Student {
    private int id;
    private String name;
    private Teacher teacher;
}

@Data
@ToString
public class Teacher {
    private int id;
    private String name;
   
}

tid是一个外键，用通常的方法：写接口-配置的xml文件-测试类查询student表信息，，这种方法查出来无法查到具有复制属性的tid

因此我们应该在Student.xml文件中通过某种方式关联上复杂属性tid才能查出来，下面有两种方式：

1.类似子查询方式

 Test.java代码：

public void testStudent(){
    SqlSession sqlSession=MybatisUtils.getSqlSession();
    StudentMapper mapper1=sqlSession.getMapper(StudentMapper.class);
    List<Student> studentList=mapper1.getStudent();
    for(Student student:studentList){
        System.out.println(student);
    }
    sqlSession.close();

}

Student.xml代码：

<!--通过子查询方式-->
    <select id="getStudent" resultMap="StudentTeacher" >
        select * from student
    </select>
    <!--    结果集查询-->
    <resultMap id="StudentTeacher" type="com.pojo.Student">
        <result property="id" column="id"/>
        <result property="name" column="name"/>
    <!--        复制的属性tid是外键，要单独处理-->
        <association property="teacher" column="tid" javaType="com.pojo.Teacher" select="getTeacher"/>
    </resultMap>
    <select id="getTeacher" resultType="com.pojo.Teacher">
        select * from teacher where id=#{id}
    </select>

2.结果集映射方式

 Test.java代码不变，Student.xml代码：

<!--    通过结果嵌套处理-->
    <select id="getStudent" resultMap="StudentTeacher2">
        select s.id sid,s.name sname,t.name tname
        from student s,teacher t where s.tid=t.id;
    </select>
    <resultMap id="StudentTeacher2" type="com.pojo.Student">
        <result property="id" column="sid"/>
        <result property="name" column="sname"/>
        <association property="teacher" javaType="com.pojo.Teacher">
            <result property="name" column="tname"/>
        </association>
    </resultMap>

查询结果：

 

复杂查询环境（一对多）

实体类准备

//一对多
@Data
@ToString
public class Student {
    private int id;
    private String name;
    private int tid;
}

@Data
@ToString
public class Teacher {
    private int id;
    private String name;
    //一个老师拥有的学生集合
    private List<Student> students;
}

   TeacherMapper接口代码：

//获取指定老师下的所有学生
Teacher getTeacher(@Param("tid") int id);

  TeacherMapper.xml代码

<!--    方式一按结果嵌套查询-->
    <select id="getTeacher" resultMap="TeacherStudent">
        select s.id sid,s.name sname,t.name tname,t.id tid
        from student s,teacher t
        where s.tid=t.id and t.id=#{tid}
    </select>

    <resultMap id="TeacherStudent" type="com.pojo.Teacher">
        <result property="id" column="tid"/>
        <result property="name" column="tname"/>
<!--        实体类teacher还有一个学生集合的属性，javaType指定属性的类型
复杂属性我们要单独处理，集合中泛型得到信息用ofType获取， private List<Student>-->
        <collection property="students" ofType="com.pojo.Student">
            <result property="id" column="sid"/>
            <result property="name" column="sname"/>
            <result property="tid" column="tid"/>
        </collection>
    </resultMap>

<!--    方式二按子查询-->
    <select id="getTeacher" resultMap="TeacherStudent">
        select * from mybatis.teacher where id=#{tid}
    </select>
    <resultMap id="TeacherStudent" type="com.pojo.Teacher">
        <collection property="students" javaType="ArrayList" ofType="Student" select="getStudentByTeacherId" column="id"/>
    </resultMap>

    <select id="getStudentByTeacherId" resultType="com.pojo.Student">
        select * from mybatis.student where tid=#{tid}
    </select>

测试代码

public void test() {
    SqlSession sqlSession = MybatisUtils.getSqlSession();
    TeacherMapper mapper = sqlSession.getMapper(TeacherMapper.class);
    Teacher teacher = mapper.getTeacher(1);
    System.out.println(teacher);
    sqlSession.close();
}

查询结果：

 关于type,resultType, ofType,javaType:

1.type在resultMap标签中使用

2.resultType用于select标签中，表示sql语句返回的对应在Java中的类型

2.ofType用来指定映射到List或集合中的pojo的类型，泛型中的约束类型

3.javaType是用来指定实体类的属性的类型

动态sql环境搭建

这部分相当于回顾之前所学

编写获取UUID的工具类

public class IDutils {
    public static String getId(){
        return UUID.randomUUID().toString().replaceAll("-","");
    }
//    @Test
//    public void test(){
//        System.out.println(IDutils.getId());
//    }
}

编写java映射数据库ORM实体类

public class Blog {
    private String id;
    private String title;
    private String author;
    private Date createTime; //属性和字段不一致
    private int views;
}

编写添加接口BlogMapper

public interface BlogMapper {
    int addBlog(Blog blog);
}

BlogMapper.xml注册sql文件

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.dao.BlogMapper">
    <insert id="addBlog" parameterType="com.pojo.Blog">
        insert into mybatis.blog(id,title,author,create_time,views)
        values(#{id},#{title},#{author},#{createTime},#{views});
    </insert>
</mapper>

测试代码：

public class Test {
    @org.junit.Test
    public void addInitBlog(){
        SqlSession sqlSession= MybatisUtils.getSqlSession();
        BlogMapper mapper=sqlSession.getMapper(BlogMapper.class);
        Blog blog=new Blog();
        blog.setId(IDutils.getId());
        blog.setTitle("MyBATIS如此简单");
        blog.setAuthor("狂");
        blog.setCreateTime(new Date());
        blog.setViews(9999);
        mapper.addBlog(blog);

        blog.setId(IDutils.getId());
        blog.setTitle("java如此简单");
        mapper.addBlog(blog);
        
        blog.setId(IDutils.getId());
        blog.setTitle("spring如此简单");
        mapper.addBlog(blog);

        blog.setId(IDutils.getId());
        blog.setTitle("vue如此简单");
        mapper.addBlog(blog);

        sqlSession.close();
    }
}

测试结果：

 

动态sql常用标签

<if>标签测试

接口

List<Blog> queryBlogIF(Map map);

对应注册文件

if标签如果满足标签内部的条件，就执行

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper
        PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN"
        "https://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.dao.BlogMapper">
    <insert id="addBlog" parameterType="com.pojo.Blog">
        insert into mybatis.blog(id,title,author,create_time,views)
        values(#{id},#{title},#{author},#{createTime},#{views});
    </insert>
    <select id="queryBlogIF" parameterType="map" resultType="com.pojo.Blog">
        select * from mybatis.blog where 1=1
        <if test="title !=null">
            and title=#{title}
        </if>
        <if test="author !=null">
            and author=#{author}
        </if>
    </select>
</mapper>

测试代码

public class Test {
    @org.junit.Test
    public  void queryBlogIF(){
        SqlSession sqlSession=MybatisUtils.getSqlSession();
        BlogMapper mapper=sqlSession.getMapper(BlogMapper.class);
        List<Blog> blogs=mapper.queryBlogIF(new HashMap());
        for(Blog blog:blogs){
            System.out.println(blog);
        }
    }
}

choose（when，otherwise）

<select id="queryBlogChoose" parameterType="map" resultType="com.pojo.Blog">
    select * from mybatis.blog
    <choose>
        <when test="title!=null">
            title=#{title}
        </when>
        <when test="author!=null">
            and author=#{author}
        </when>
        <otherwise>
            and views=#{views}
        </otherwise>
    </choose>
</select>

测试代码

@org.junit.Test
public void queryBlogChoose(){
    SqlSession sqlSession=MybatisUtils.getSqlSession();
    BlogMapper mapper=sqlSession.getMapper(BlogMapper.class);
    Map map=new HashMap();
    List<Blog> blogs=mapper.queryBlogIF(map);
    for(Blog blog:blogs){
        System.out.println(blog);
    }
    sqlSession.close();

}

trim（where，set）

1.where元素只会在至少一个子元素的条件返回sql子句的情况下才去插入where子句，而且若语句开头为and或者or，where元素会自动将其去掉，如：

 

2.set+<update>标签

接口

int updateBlog(Map map);

xml代码

<update id="updateBlog" parameterType="map">
    update mybatis.blog
    <set>
        <if test="title!=null">
            title=#{title},
        </if>
        <if test="author!=null">
            author=#{author}
        </if>
    </set>
    where id=#{id}
</update>

测试代码

public void updateBlog(){
    SqlSession sqlSession=MybatisUtils.getSqlSession();
    BlogMapper mapper=sqlSession.getMapper(BlogMapper.class);
    Map map=new HashMap();
    map.put("title","vue如此简单2"); //相当于显示条件，只查找title="java如此简单"的记录
    map.put("id","0ae64f7aa9c94d2e8b10046d902dc4cd");
    mapper.updateBlog(map);
    sqlSession.close();
}

运行结果：

 解决代码冗余<sql>标签和<include>标签

将重复的代码提取出来用sql标签包装，在需要使用的地方用include标签使用

如

<foreach>标签

接口

List<Blog> queryBlogForEach(Map map);

xml代码

<select id="queryBlogForEach" parameterType="map" resultType="com.pojo.Blog">
    select * from mybatis.blog
    <where>
        <foreach collection="ids" item="id" open="and (" close=")" separator="or">
            id=#{id}
        </foreach>
    </where>
</select>

测试代码

@org.junit.Test
public void queryBlogForEach(){
    SqlSession sqlSession=MybatisUtils.getSqlSession();
    BlogMapper mapper=sqlSession.getMapper(BlogMapper.class);
    Map map=new HashMap();
    ArrayList<Integer> ids=new ArrayList<Integer>();//存放interger的一个列表list
    ids.add(1);
    ids.add(2);
    map.put("ids",ids);
    List<Blog> blogs=mapper.queryBlogForEach(map);
    for(Blog blog:blogs){
        System.out.println(blog);
    }
    sqlSession.close();
}

    

运行结果