Mybatis介绍(一)

这里介绍的mybatis比较简单, 我做为一个初学者, 记录下个人在学习中方法, 如果那里出错, 希望读者朋友们见谅.

首先这里介绍一下我们下面用的表结构：

author表是保存了作者的个人信息, 因为我们在这里做测试, 所以就简单的定义几个字段.

blog表是保存谁写了博客的内容, 这里也是几个简单的字段.

comment表是保存对哪篇博客评论, 也是几个简单的字段.

注意: 这三张表的id都是自增型, 你也可以做其他的改变, 这里是为了方便.

下面给出了几张表格创建的sql语句:

CREATE TABLE `author` (

   `id` int(11) NOT NULL AUTO_INCREMENT,

   `name` varchar(25) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,

   `age` int(5) NULL DEFAULT NULL,

   `email` varchar(30) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,

   `country` varchar(10) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,

   PRIMARY KEY (`id`)

);

CREATE TABLE `blog` (

   `id` int(11) NOT NULL AUTO_INCREMENT,

   `authorid` int(11) NULL DEFAULT NULL,

   `title` varchar(35) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,

   `mainbody` text CHARACTER SET utf8 COLLATE utf8_general_ci NULL,

   `creattime` varchar(70) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,

   PRIMARY KEY (`id`)

);

CREATE TABLE `comment` (

   `id` int(11) NOT NULL AUTO_INCREMENT,

   `blogid` int(11) NULL DEFAULT NULL,

   `content` text CHARACTER SET utf8 COLLATE utf8_general_ci NULL,

   `creattime` varchar(50) CHARACTER SET utf8 COLLATE utf8_general_ci NULL DEFAULT NULL,

   PRIMARY KEY (`id`)

);

使用maven+springmvc+mabatis+spring搭建web环境, 可以参考博客: https://www.cnblogs.com/jay36/p/7762448.html, 这里就不详细的介绍了.

这里主要介绍mybatis的用法, 首先使用Mybatis Generator生成pojo/dao/mapping三个文件, 即实体类、DAO接口和Mapping映射文件.

可以参考博客: https://blog.csdn.net/zhshulin/article/details/23912615, 下面就开始简单介绍Mybatis的使用.

1. 看一下三个表pojo(Plain Ordinary Java Object), 即实体类

package com.springdemo.pojo;

public class Author {

    private Integer id;

    private String name;

    private Integer age;

    private String email;

    private String country;

    /* getting and setting function */

}

package com.springdemo.pojo;

public class Blog {

    private Integer id;

    private Integer authorid;

    private String title;

    private String creattime;

    private String mainbody;

    /* getting and setting function */

}

package com.springdemo.pojo;

public class Comment {

    private Integer id;

    private Integer blogid;

    private String creattime;

    private String content;

    /* getting and setting function */

}

2. 再看一下三个表的dao(Data Access Object), 即dao接口

package com.springdemo.dao

public interface AuthorMapper {

    int deleteByPrimaryKey(Integer id);

    int insert(Author record);

    int insertSelective(Author record);

    Author selectByPrimaryKey(Integer id);

    int updateByPrimaryKeySelective(Author record);

    int updateByPrimaryKey(Author record);

}

package com.springdemo.dao

public interface BlogMapper {

    int deleteByPrimaryKey(Integer id);

    int insert(Blog record);

    int insertSelective(Blog record);

    Blog selectByPrimaryKey(Integer id);

    int updateByPrimaryKeySelective(Blog record);

    int updateByPrimaryKeyWithBLOBs(Blog record);

    int updateByPrimaryKey(Blog record);

}

package com.springdemo.dao

public interface CommentMapper {

    int deleteByPrimaryKey(Integer id);

    int insert(Comment record);

    int insertSelective(Comment record);

    Comment selectByPrimaryKey(Integer id);

    int updateByPrimaryKeySelective(Comment record);

    int updateByPrimaryKeyWithBLOBs(Comment record);

    int updateByPrimaryKey(Comment record);

}

3. 再看一下三个表的mapping, 即Mapping映射

<?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.springdemo.dao.AuthorMapper" >

  <resultMap id="BaseResultMap" type="com.springdemo.pojo.Author" >

    <id column="id" property="id" jdbcType="INTEGER" />

    <result column="name" property="name" jdbcType="VARCHAR" />

    <result column="age" property="age" jdbcType="INTEGER" />

    <result column="email" property="email" jdbcType="VARCHAR" />

    <result column="country" property="country" jdbcType="VARCHAR" />

  </resultMap>

  <sql id="Base_Column_List" >

    id, name, age, email, country

  </sql>

  <select id="selectByPrimaryKey" resultMap="BaseResultMap" parameterType="java.lang.Integer" >

    select

    <include refid="Base_Column_List" />

    from author

    where id = #{id,jdbcType=INTEGER}

  </select>

  <delete id="deleteByPrimaryKey" parameterType="java.lang.Integer" >

    delete from author

    where id = #{id,jdbcType=INTEGER}

  </delete>

  <insert id="insert" parameterType="com.springdemo.pojo.Author" >

    insert into author (id, name, age,

      email, country)

    values (#{id,jdbcType=INTEGER}, #{name,jdbcType=VARCHAR}, #{age,jdbcType=INTEGER},

      #{email,jdbcType=VARCHAR}, #{country,jdbcType=VARCHAR})

  </insert>

  <insert id="insertSelective" parameterType="com.springdemo.pojo.Author" >

    insert into author

    <trim prefix="(" suffix=")" suffixOverrides="," >

      <if test="id != null" >

        id,

      </if>

      <if test="name != null" >

        name,

      </if>

      <if test="age != null" >

        age,

      </if>

      <if test="email != null" >

        email,

      </if>

      <if test="country != null" >

        country,

      </if>

    </trim>

    <trim prefix="values (" suffix=")" suffixOverrides="," >

      <if test="id != null" >

        #{id,jdbcType=INTEGER},

      </if>

      <if test="name != null" >

        #{name,jdbcType=VARCHAR},

      </if>

      <if test="age != null" >

        #{age,jdbcType=INTEGER},

      </if>

      <if test="email != null" >

        #{email,jdbcType=VARCHAR},

      </if>

      <if test="country != null" >

        #{country,jdbcType=VARCHAR},

      </if>

    </trim>

  </insert>

  <update id="updateByPrimaryKeySelective" parameterType="com.springdemo.pojo.Author" >

    update author

    <set >

      <if test="name != null" >

        name = #{name,jdbcType=VARCHAR},

      </if>

      <if test="age != null" >

        age = #{age,jdbcType=INTEGER},

      </if>

      <if test="email != null" >

        email = #{email,jdbcType=VARCHAR},

      </if>

      <if test="country != null" >

        country = #{country,jdbcType=VARCHAR},

      </if>

    </set>

    where id = #{id,jdbcType=INTEGER}

  </update>

  <update id="updateByPrimaryKey" parameterType="com.springdemo.pojo.Author" >

    update author

    set name = #{name,jdbcType=VARCHAR},

      age = #{age,jdbcType=INTEGER},

      email = #{email,jdbcType=VARCHAR},

      country = #{country,jdbcType=VARCHAR}

    where id = #{id,jdbcType=INTEGER}

  </update>

</mapper>

<?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.springdemo.dao.BlogMapper" >

  <resultMap id="BaseResultMap" type="com.springdemo.pojo.Blog" >

    <id column="id" property="id" jdbcType="INTEGER" />

    <result column="authorid" property="authorid" jdbcType="INTEGER" />

    <result column="title" property="title" jdbcType="VARCHAR" />

    <result column="creattime" property="creattime" jdbcType="VARCHAR" />

  </resultMap>

  <resultMap id="ResultMapWithBLOBs" type="com.springdemo.pojo.Blog" extends="BaseResultMap" >

    <result column="mainbody" property="mainbody" jdbcType="LONGVARCHAR" />

  </resultMap>

  <sql id="Base_Column_List" >

    id, authorid, title, creattime

  </sql>

  <sql id="Blob_Column_List" >

    mainbody

  </sql>

  <select id="selectByPrimaryKey" resultMap="ResultMapWithBLOBs" parameterType="java.lang.Integer" >

    select

    <include refid="Base_Column_List" />

    ,

    <include refid="Blob_Column_List" />

    from blog

    where id = #{id,jdbcType=INTEGER}

  </select>

  <delete id="deleteByPrimaryKey" parameterType="java.lang.Integer" >

    delete from blog

    where id = #{id,jdbcType=INTEGER}

  </delete>

  <insert id="insert" parameterType="com.springdemo.pojo.Blog" >

    insert into blog (id, authorid, title,

      creattime, mainbody)

    values (#{id,jdbcType=INTEGER}, #{authorid,jdbcType=INTEGER}, #{title,jdbcType=VARCHAR},

      #{creattime,jdbcType=VARCHAR}, #{mainbody,jdbcType=LONGVARCHAR})

  </insert>

  <insert id="insertSelective" parameterType="com.springdemo.pojo.Blog" >

    insert into blog

    <trim prefix="(" suffix=")" suffixOverrides="," >

      <if test="id != null" >

        id,

      </if>

      <if test="authorid != null" >

        authorid,

      </if>

      <if test="title != null" >

        title,

      </if>

      <if test="creattime != null" >

        creattime,

      </if>

      <if test="mainbody != null" >

        mainbody,

      </if>

    </trim>

    <trim prefix="values (" suffix=")" suffixOverrides="," >

      <if test="id != null" >

        #{id,jdbcType=INTEGER},

      </if>

      <if test="authorid != null" >

        #{authorid,jdbcType=INTEGER},

      </if>

      <if test="title != null" >

        #{title,jdbcType=VARCHAR},

      </if>

      <if test="creattime != null" >

        #{creattime,jdbcType=VARCHAR},

      </if>

      <if test="mainbody != null" >

        #{mainbody,jdbcType=LONGVARCHAR},

      </if>

    </trim>

  </insert>

  <update id="updateByPrimaryKeySelective" parameterType="com.springdemo.pojo.Blog" >

    update blog

    <set >

      <if test="authorid != null" >

        authorid = #{authorid,jdbcType=INTEGER},

      </if>

      <if test="title != null" >

        title = #{title,jdbcType=VARCHAR},

      </if>

      <if test="creattime != null" >

        creattime = #{creattime,jdbcType=VARCHAR},

      </if>

      <if test="mainbody != null" >

        mainbody = #{mainbody,jdbcType=LONGVARCHAR},

      </if>

    </set>

    where id = #{id,jdbcType=INTEGER}

  </update>

  <update id="updateByPrimaryKeyWithBLOBs" parameterType="com.springdemo.pojo.Blog" >

    update blog

    set authorid = #{authorid,jdbcType=INTEGER},

      title = #{title,jdbcType=VARCHAR},

      creattime = #{creattime,jdbcType=VARCHAR},

      mainbody = #{mainbody,jdbcType=LONGVARCHAR}

    where id = #{id,jdbcType=INTEGER}

  </update>

  <update id="updateByPrimaryKey" parameterType="com.springdemo.pojo.Blog" >

    update blog

    set authorid = #{authorid,jdbcType=INTEGER},

      title = #{title,jdbcType=VARCHAR},

      creattime = #{creattime,jdbcType=VARCHAR}

    where id = #{id,jdbcType=INTEGER}

  </update>

</mapper>

<?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.springdemo.dao.CommentMapper" >

  <resultMap id="BaseResultMap" type="com.springdemo.pojo.Comment" >

    <id column="id" property="id" jdbcType="INTEGER" />

    <result column="blogid" property="blogid" jdbcType="INTEGER" />

    <result column="creattime" property="creattime" jdbcType="VARCHAR" />

  </resultMap>

  <resultMap id="ResultMapWithBLOBs" type="com.springdemo.pojo.Comment" extends="BaseResultMap" >

    <result column="content" property="content" jdbcType="LONGVARCHAR" />

  </resultMap>

  <sql id="Base_Column_List" >

    id, blogid, creattime

  </sql>

  <sql id="Blob_Column_List" >

    content

  </sql>

  <select id="selectByPrimaryKey" resultMap="ResultMapWithBLOBs" parameterType="java.lang.Integer" >

    select

    <include refid="Base_Column_List" />

    ,

    <include refid="Blob_Column_List" />

    from comment

    where id = #{id,jdbcType=INTEGER}

  </select>

  <delete id="deleteByPrimaryKey" parameterType="java.lang.Integer" >

    delete from comment

    where id = #{id,jdbcType=INTEGER}

  </delete>

  <insert id="insert" parameterType="com.springdemo.pojo.Comment" >

    insert into comment (id, blogid, creattime,

      content)

    values (#{id,jdbcType=INTEGER}, #{blogid,jdbcType=INTEGER}, #{creattime,jdbcType=VARCHAR},

      #{content,jdbcType=LONGVARCHAR})

  </insert>

  <insert id="insertSelective" parameterType="com.springdemo.pojo.Comment" >

    insert into comment

    <trim prefix="(" suffix=")" suffixOverrides="," >

      <if test="id != null" >

        id,

      </if>

      <if test="blogid != null" >

        blogid,

      </if>

      <if test="creattime != null" >

        creattime,

      </if>

      <if test="content != null" >

        content,

      </if>

    </trim>

    <trim prefix="values (" suffix=")" suffixOverrides="," >

      <if test="id != null" >

        #{id,jdbcType=INTEGER},

      </if>

      <if test="blogid != null" >

        #{blogid,jdbcType=INTEGER},

      </if>

      <if test="creattime != null" >

        #{creattime,jdbcType=VARCHAR},

      </if>

      <if test="content != null" >

        #{content,jdbcType=LONGVARCHAR},

      </if>

    </trim>

  </insert>

  <update id="updateByPrimaryKeySelective" parameterType="com.springdemo.pojo.Comment" >

    update comment

    <set >

      <if test="blogid != null" >

        blogid = #{blogid,jdbcType=INTEGER},

      </if>

      <if test="creattime != null" >

        creattime = #{creattime,jdbcType=VARCHAR},

      </if>

      <if test="content != null" >

        content = #{content,jdbcType=LONGVARCHAR},

      </if>

    </set>

    where id = #{id,jdbcType=INTEGER}

  </update>

  <update id="updateByPrimaryKeyWithBLOBs" parameterType="com.springdemo.pojo.Comment" >

    update comment

    set blogid = #{blogid,jdbcType=INTEGER},

      creattime = #{creattime,jdbcType=VARCHAR},

      content = #{content,jdbcType=LONGVARCHAR}

    where id = #{id,jdbcType=INTEGER}

  </update>

  <update id="updateByPrimaryKey" parameterType="com.springdemo.pojo.Comment" >

    update comment

    set blogid = #{blogid,jdbcType=INTEGER},

      creattime = #{creattime,jdbcType=VARCHAR}

    where id = #{id,jdbcType=INTEGER}

  </update>

</mapper>

mybatis的使用, 关键在于要要写好mapping映射, 使用工具生成的是最简单的curd的方法, 现在我们来增加一个我们自定义的方法.

首先在mapping的文件中写一个映射, 我们就在BlogMapper.xml文件中写,代码如下:

<?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.springdemo.dao.BlogMapper" >

  ......

  <insert id="insertBlogByList" useGeneratedKeys="true"

    keyProperty="id" parameterType="java.util.List">

      insert into blog (authorid, title, creattime, mainbody) values

      <foreach item="item" collection="list" separator=",">

        (#{item.authorid,jdbcType=INTEGER}, #{item.title,jdbcType=VARCHAR},

        #{item.creattime,jdbcType=VARCHAR}, #{item.mainbody,jdbcType=LONGVARCHAR})

      </foreach>

  </insert>

  ......

</mapper>

这段xml的代码主要就是批量插入数据, 而且id是自增长的,  数据以list的形式传入进来, 然后循环插入到blog表中.

然后我们要在BlogMapper.java的dao中加一个接口, 代码如下:

package com.springdemo.dao;

public interface BlogMapper {

    ......

    int insertBlogByList(List<Blog> listBlog);

    ......

}
注意这里的接口名字要和我们之前在xml中加入的id值相同才行, 因为这样mybatis才会映射.
即在BlogMapper.xml中写的insert语句id是insertBlogByList, 
那么这里的定义的接口必须也是这个, 而且参数的类型也必须一样, 这一点切记。

最后我们要在controller中去调用(因为这里我是用springmvc写的,所有用mvc思想去写调用,你也可以随便写一个方法去调用, 这里给出我的调用方法):

//下面是BlogController.java的代码

package com.springdemo.controller;

@Controller

@RequestMapping(value = "/blog")

public class BlogController {

    private static final Logger LOG = LogManager.getLogger();

    @Autowired

    private BlogService blogService;

　　 //这里是把前端的值获取到,然后再存入到数据库中, 最后返回状态

    @RequestMapping(value="/insert", method = RequestMethod.POST)

    public void insertBlog(HttpServletRequest request, HttpServletResponse response) {

        String status = "{\"status\":\"failure\"}";

        int authorid = Integer.parseInt(request.getParameter("authorid"));

        String title = String.valueOf(request.getParameter("title"));

        String mainbody = String.valueOf(request.getParameter("mainbody"));

        SimpleDateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");

        Date now = new Date();

        String creattime = df.format(now);

        List<Blog> listBlog = new ArrayList<Blog>();

        Blog blog = new Blog();

        blog.setAuthorid(authorid);

        blog.setTitle(title);

        blog.setMainbody(mainbody);

        blog.setCreattime(creattime);

        listBlog.add(blog);

        int affectRow = blogService.insertBlogByList(listBlog);

        if (affectRow != 0) {

            status = "{\"status\":\"success\"}";

        }

        response.setContentType("text/html;UTF-8");

        try (PrintWriter writer = response.getWriter();) {

            writer.write(status);

            writer.flush();

        } catch (IOException e) {

            LOG.error(e.getMessage(), e);

        }

    }

}

----------------------------------------------------------

// 下面是BlogService.java的代码

package com.springdemo.service;

import java.util.List;


// 这里不需要继承BlogMapper接口, 通过spring注解直接使用

@Service(value="blogService")

public class BlogService {

    @Resource

    private BlogMapper blogMapper;

    public int insertBlogByList(List<Blog> listBlog) {

        int affectRow = 0;

        affectRow = this.blogMapper.insertBlogByList(listBlog);

        return affectRow;

    }

}

这样就简单的完成了在xml中建立sql语句, 然后通过映射转换到java中, 最后去执行.

待续......

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