【Mybatis】深入浅出Mybatis（十）——逆向工程

小咪咪 2022-09-28 13:10 227阅读 0赞

# 一、前言 #

前一篇博客中，小编向大家介绍了一下[Mybatis和hibernate的对比][Mybatis_hibernate]，在这一篇博客说说mybatis的逆向工程，展示一下，一个非常让你惊讶的技术，只要你有一个数据库，你的持久层，你的D层从此不用你自己手写了。

# 二、什么是逆向工程？ #

mybaits需要程序员自己编写sql语句，mybatis官方提供逆向工程 可以针对单表自动生成mybatis执行所需要的代码（mapper.java,mapper.xml、po..），企业实际开发中，常用的逆向工程方式：由于数据库的表生成java代码。

# 三、Mybatis中逆向工程的使用 #

## 3.1 前期准备 ##

*  Mybatis生成核心帮助文档 ，[下载点击这里][Link 1]
 *  自动生成功能的java Project，[下载点击这里][Link 2]

![这里写图片描述][20170311220729610]

![这里写图片描述][20170311220748766]

![这里写图片描述][20170311220759594]

## 3.2 导入 ##

*  导入已有的数据库，小编已经导入自己编写好的数据库，数据库结构如下：

![这里写图片描述][20170311221016298]

*  把generatorSqlmapCustom JavaProject导入eclipse

![这里写图片描述][SouthEast]

## 3.3 需要修改的文件 ##

先要查找数据库配置文件是哪一个，在GeneratorSqlmap.java中可以查找到。

![这里写图片描述][SouthEast 1]

*  修改配置文件的数据库连接以及数据库

![这里写图片描述][SouthEast 2]

*  指定数据库表

<table tableName="items"></table>
            <table tableName="orders"></table>
            <table tableName="orderdetail"></table>
            <table tableName="user"></table>

*  生成表对应的实体类

<javaModelGenerator targetPackage="cn.itcast.ssm.po" targetProject=".\src">
                
                <property name="enableSubPackages" value="false" />
                
                <property name="trimStrings" value="true" />
            </javaModelGenerator>

*  mapper映射文件生成

<sqlMapGenerator targetPackage="cn.itcast.ssm.mapper" targetProject=".\src">
                
                <property name="enableSubPackages" value="false" />
            </sqlMapGenerator>

*  mapper接口生成

<javaClientGenerator type="XMLMAPPER" targetPackage="cn.itcast.ssm.mapper" targetProject=".\src">
                
                <property name="enableSubPackages" value="false" />
            </javaClientGenerator>

*  几个关键属性：

javaModelGenerator ：实体类生成；

sqlMapGenerator ：映射文件生成；

javaClientGenerator ：接口生成；

targetProject：生成文件的位置，本例中.\\src，是指src下的目录；

targetPackage：生成包的名称；

修改完成后，运行GeneratorSqlmap.java中的main方法，就可以生成。

## 3.4 生成文件展示 ##

宏观展示：

![这里写图片描述][SouthEast 3]

以User表为例，展示生成的代码：

*  User.java

package cn.itcast.ssm.po;
    
    import java.util.Date;
    
    public class User { 
        private Integer id;
    
        private String username;
    
        private Date birthday;
    
        private String sex;
    
        private String address;
    
        public Integer getId() {
            return id;
        }
    
        public void setId(Integer id) {
            this.id = id;
        }
    
        public String getUsername() {
            return username;
        }
    
        public void setUsername(String username) {
            this.username = username == null ? null : username.trim();
        }
    
        public Date getBirthday() {
            return birthday;
        }
    
        public void setBirthday(Date birthday) {
            this.birthday = birthday;
        }
    
        public String getSex() {
            return sex;
        }
    
        public void setSex(String sex) {
            this.sex = sex == null ? null : sex.trim();
        }
    
        public String getAddress() {
            return address;
        }
    
        public void setAddress(String address) {
            this.address = address == null ? null : address.trim();
        }
    }

*  UserMapper.java

这里生成了所有的增删改查的sql语句，调用的时候就直接使用对应的方法就可以了。很方便吧。（这里可以重点学习一下，看自动生成的代码是如何封装的，自己要认真学习一下哦）

package cn.itcast.ssm.mapper;
    
    import cn.itcast.ssm.po.User;
    import cn.itcast.ssm.po.UserExample;
    import java.util.List;
    import org.apache.ibatis.annotations.Param;
    
    public interface UserMapper { 
        int countByExample(UserExample example);
    
        int deleteByExample(UserExample example);
    
        int deleteByPrimaryKey(Integer id);
    
        int insert(User record);
    
        int insertSelective(User record);
    
        List<User> selectByExample(UserExample example);
    
        User selectByPrimaryKey(Integer id);
    
        int updateByExampleSelective(@Param("record") User record, @Param("example") UserExample example);
    
        int updateByExample(@Param("record") User record, @Param("example") UserExample example);
    
        int updateByPrimaryKeySelective(User record);
    
        int updateByPrimaryKey(User record);
    }

*  UserMapper.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="cn.itcast.ssm.mapper.UserMapper" >
      <resultMap id="BaseResultMap" type="cn.itcast.ssm.po.User" >
        <id column="id" property="id" jdbcType="INTEGER" />
        <result column="username" property="username" jdbcType="VARCHAR" />
        <result column="birthday" property="birthday" jdbcType="DATE" />
        <result column="sex" property="sex" jdbcType="CHAR" />
        <result column="address" property="address" jdbcType="VARCHAR" />
      </resultMap>
      <sql id="Example_Where_Clause" >
        <where >
          <foreach collection="oredCriteria" item="criteria" separator="or" >
            <if test="criteria.valid" >
              <trim prefix="(" suffix=")" prefixOverrides="and" >
                <foreach collection="criteria.criteria" item="criterion" >
                  <choose >
                    <when test="criterion.noValue" >
                      and ${criterion.condition}
                    </when>
                    <when test="criterion.singleValue" >
                      and ${criterion.condition} #{criterion.value}
                    </when>
                    <when test="criterion.betweenValue" >
                      and ${criterion.condition} #{criterion.value} and #{criterion.secondValue}
                    </when>
                    <when test="criterion.listValue" >
                      and ${criterion.condition}
                      <foreach collection="criterion.value" item="listItem" open="(" close=")" separator="," >
                        #{listItem}
                      </foreach>
                    </when>
                  </choose>
                </foreach>
              </trim>
            </if>
          </foreach>
        </where>
      </sql>
      <sql id="Update_By_Example_Where_Clause" >
        <where >
          <foreach collection="example.oredCriteria" item="criteria" separator="or" >
            <if test="criteria.valid" >
              <trim prefix="(" suffix=")" prefixOverrides="and" >
                <foreach collection="criteria.criteria" item="criterion" >
                  <choose >
                    <when test="criterion.noValue" >
                      and ${criterion.condition}
                    </when>
                    <when test="criterion.singleValue" >
                      and ${criterion.condition} #{criterion.value}
                    </when>
                    <when test="criterion.betweenValue" >
                      and ${criterion.condition} #{criterion.value} and #{criterion.secondValue}
                    </when>
                    <when test="criterion.listValue" >
                      and ${criterion.condition}
                      <foreach collection="criterion.value" item="listItem" open="(" close=")" separator="," >
                        #{listItem}
                      </foreach>
                    </when>
                  </choose>
                </foreach>
              </trim>
            </if>
          </foreach>
        </where>
      </sql>
      <sql id="Base_Column_List" >
        id, username, birthday, sex, address
      </sql>
      <select id="selectByExample" resultMap="BaseResultMap" parameterType="cn.itcast.ssm.po.UserExample" >
        select
        <if test="distinct" >
          distinct
        </if>
        <include refid="Base_Column_List" />
        from user
        <if test="_parameter != null" >
          <include refid="Example_Where_Clause" />
        </if>
        <if test="orderByClause != null" >
          order by ${orderByClause}
        </if>
      </select>
      <select id="selectByPrimaryKey" resultMap="BaseResultMap" parameterType="java.lang.Integer" >
        select 
        <include refid="Base_Column_List" />
        from user
        where id = #{id,jdbcType=INTEGER}
      </select>
      <delete id="deleteByPrimaryKey" parameterType="java.lang.Integer" >
        delete from user
        where id = #{id,jdbcType=INTEGER}
      </delete>
      <delete id="deleteByExample" parameterType="cn.itcast.ssm.po.UserExample" >
        delete from user
        <if test="_parameter != null" >
          <include refid="Example_Where_Clause" />
        </if>
      </delete>
      <insert id="insert" parameterType="cn.itcast.ssm.po.User" >
        insert into user (id, username, birthday, 
          sex, address)
        values (#{id,jdbcType=INTEGER}, #{username,jdbcType=VARCHAR}, #{birthday,jdbcType=DATE}, 
          #{sex,jdbcType=CHAR}, #{address,jdbcType=VARCHAR})
      </insert>
      <insert id="insertSelective" parameterType="cn.itcast.ssm.po.User" >
        insert into user
        <trim prefix="(" suffix=")" suffixOverrides="," >
          <if test="id != null" >
            id,
          </if>
          <if test="username != null" >
            username,
          </if>
          <if test="birthday != null" >
            birthday,
          </if>
          <if test="sex != null" >
            sex,
          </if>
          <if test="address != null" >
            address,
          </if>
        </trim>
        <trim prefix="values (" suffix=")" suffixOverrides="," >
          <if test="id != null" >
            #{id,jdbcType=INTEGER},
          </if>
          <if test="username != null" >
            #{username,jdbcType=VARCHAR},
          </if>
          <if test="birthday != null" >
            #{birthday,jdbcType=DATE},
          </if>
          <if test="sex != null" >
            #{sex,jdbcType=CHAR},
          </if>
          <if test="address != null" >
            #{address,jdbcType=VARCHAR},
          </if>
        </trim>
      </insert>
      <select id="countByExample" parameterType="cn.itcast.ssm.po.UserExample" resultType="java.lang.Integer" >
        select count(*) from user
        <if test="_parameter != null" >
          <include refid="Example_Where_Clause" />
        </if>
      </select>
      <update id="updateByExampleSelective" parameterType="map" >
        update user
        <set >
          <if test="record.id != null" >
            id = #{record.id,jdbcType=INTEGER},
          </if>
          <if test="record.username != null" >
            username = #{record.username,jdbcType=VARCHAR},
          </if>
          <if test="record.birthday != null" >
            birthday = #{record.birthday,jdbcType=DATE},
          </if>
          <if test="record.sex != null" >
            sex = #{record.sex,jdbcType=CHAR},
          </if>
          <if test="record.address != null" >
            address = #{record.address,jdbcType=VARCHAR},
          </if>
        </set>
        <if test="_parameter != null" >
          <include refid="Update_By_Example_Where_Clause" />
        </if>
      </update>
      <update id="updateByExample" parameterType="map" >
        update user
        set id = #{record.id,jdbcType=INTEGER},
          username = #{record.username,jdbcType=VARCHAR},
          birthday = #{record.birthday,jdbcType=DATE},
          sex = #{record.sex,jdbcType=CHAR},
          address = #{record.address,jdbcType=VARCHAR}
        <if test="_parameter != null" >
          <include refid="Update_By_Example_Where_Clause" />
        </if>
      </update>
      <update id="updateByPrimaryKeySelective" parameterType="cn.itcast.ssm.po.User" >
        update user
        <set >
          <if test="username != null" >
            username = #{username,jdbcType=VARCHAR},
          </if>
          <if test="birthday != null" >
            birthday = #{birthday,jdbcType=DATE},
          </if>
          <if test="sex != null" >
            sex = #{sex,jdbcType=CHAR},
          </if>
          <if test="address != null" >
            address = #{address,jdbcType=VARCHAR},
          </if>
        </set>
        where id = #{id,jdbcType=INTEGER}
      </update>
      <update id="updateByPrimaryKey" parameterType="cn.itcast.ssm.po.User" >
        update user
        set username = #{username,jdbcType=VARCHAR},
          birthday = #{birthday,jdbcType=DATE},
          sex = #{sex,jdbcType=CHAR},
          address = #{address,jdbcType=VARCHAR}
        where id = #{id,jdbcType=INTEGER}
      </update>
    </mapper>

# 四、小结 #

逆向工程在很多软件里面都有，比如EA的逆向工程，PB的逆向工程。还有很多，总之，这个就是其中的一些很有价值的东西，在企业运用的时候很方便，而且这些生成好的类，尽量不要去修改，如果非要修改的话，可以用pv类来实现继承拓展。这是很好的选择。

下一篇将向大家带来Mybatis和Spring的结合。

[Mybatis_hibernate]: http://blog.csdn.net/kisscatforever/article/details/60958927
[Link 1]: http://url.cn/45sv5XX
[Link 2]: http://url.cn/45sv0p3
[20170311220729610]: /images/20220708/41718f84292c4200882dbd9f66cad032.png
[20170311220748766]: /images/20220708/a4ea99970eaf4dfb83f607e6c07dfe50.png?
[20170311220759594]: /images/20220708/0d87834a99014743a99e84dbc1830478.png?
[20170311221016298]: /images/20220708/64e38e22efdf4e249aa0bc53ebf89768.png?
[SouthEast]: /images/20220708/4eac8ca9eef747fd8114d344d61dab8d.png
[SouthEast 1]: /images/20220708/dbefe1d124144d6782c2b8192ccb718a.png
[SouthEast 2]: /images/20220708/2a6052fff7c4471b86dfdef0428d3a20.png
[SouthEast 3]: /images/20220708/5f9be0ead1854d36ba21aeaa78f591ec.png