深入浅出Mybatis(九)逆向工程

一，    前一篇博客中，介绍了一下Mybatis和hibernate的对比，在这一篇博客说说mybatis的逆向工程，展示一下，只要有一个数据库，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、pojo），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

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：

把generatorSqlmapCustom JavaProject导入

修改配置文件的数据库连接以及数据库

指定数据库表

生成表对应的实体类

<javaModelGenerator targetPackage="com.dtt.mybatis.pojo"
			targetProject=".src">
			<!-- enableSubPackages:是否让schema作为包的后缀 -->
			<property name="enableSubPackages" value="false" />
			<!-- 从数据库返回的值被清理前后的空格 -->
			<property name="trimStrings" value="true" />
</javaModelGenerator>

 mapper映射文件生成

<!-- targetProject:mapper映射文件生成的位置 -->
		<sqlMapGenerator targetPackage="com.dtt.mybatis.mapper"
			targetProject=".src">
			<!-- enableSubPackages:是否让schema作为包的后缀 -->
			<property name="enableSubPackages" value="false" />
		</sqlMapGenerator>

 mapper接口生成

<!-- targetPackage：mapper接口生成的位置 -->
		<javaClientGenerator type="XMLMAPPER"
			targetPackage="com.dtt.mybatis.mapper"
			targetProject=".src">
			<!-- enableSubPackages:是否让schema作为包的后缀 -->
			<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。

 以User表为例，展示生成的代码：

• User.java

  package com.dtt.mybatis.pojo;
  
  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。（重点学习一下自动生成的代码是如何封装的）

  package com.dtt.mybatis.mapper;
  
  import com.dtt.mybatis.pojo.User;
  import com.dtt.mybatis.pojo.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="com.dtt.mybatis.mapper.UserMapper" >
    <resultMap id="BaseResultMap" type="com.dtt.mybatis.pojo.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="com.dtt.mybatis.pojo.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="com.dtt.mybatis.pojo.UserExample" >
      delete from user
      <if test="_parameter != null" >
        <include refid="Example_Where_Clause" />
      </if>
    </delete>
    <insert id="insert" parameterType="com.dtt.mybatis.pojo.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="com.dtt.mybatis.pojo.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="com.dtt.mybatis.pojo.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="com.dtt.mybatis.pojo.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="com.dtt.mybatis.pojo.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>
   

  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。