之前在項目中用到mybtis操作數據庫時都是手動寫sql,對於我這種sql水平不是很好地人來說痛苦死了；動態查詢的sql我表示到現在還不會寫呀！
還好，利用數據庫表反向生成的工具可以幫我解決大部分的sql;(mybatis generator 你懂的)
首先利用反向生成可以幫我們自動生成實體類，dao接口，dao映射文件；
在dao映射文件如下所示：
<?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="bz.sunlight.dao.UserMapper" >
<resultMap id="BaseResultMap" type="bz.sunlight.entity.User" >
<!--
WARNING - @mbggenerated
This element is automatically generated by MyBatis Generator, do not modify.
This element was generated on Sat Aug 27 23:42:15 CST 2016.
-->
<id column="id" property="id" jdbcType="VARCHAR" />
<result column="name" property="name" jdbcType="VARCHAR" />
<result column="password" property="password" jdbcType="VARCHAR" />
</resultMap>
<sql id="Example_Where_Clause" >
<!--
WARNING - @mbggenerated
This element is automatically generated by MyBatis Generator, do not modify.
This element was generated on Sat Aug 27 23:42:15 CST 2016.
-->
<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" >
<!--
WARNING - @mbggenerated
This element is automatically generated by MyBatis Generator, do not modify.
This element was generated on Sat Aug 27 23:42:15 CST 2016.
-->
<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" >
<!--
WARNING - @mbggenerated
This element is automatically generated by MyBatis Generator, do not modify.
This element was generated on Sat Aug 27 23:42:15 CST 2016.
-->
id, name, password
</sql>
<select id="selectByExample" resultMap="BaseResultMap" parameterType="bz.sunlight.entity.UserExample" >
<!--
WARNING - @mbggenerated
This element is automatically generated by MyBatis Generator, do not modify.
This element was generated on Sat Aug 27 23:42:15 CST 2016.
-->
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.String" >
<!--
WARNING - @mbggenerated
This element is automatically generated by MyBatis Generator, do not modify.
This element was generated on Sat Aug 27 23:42:15 CST 2016.
-->
select
<include refid="Base_Column_List" />
from user
where id = #{id,jdbcType=VARCHAR}
</select>
<delete id="deleteByPrimaryKey" parameterType="java.lang.String" >
<!--
WARNING - @mbggenerated
This element is automatically generated by MyBatis Generator, do not modify.
This element was generated on Sat Aug 27 23:42:15 CST 2016.
-->
delete from user
where id = #{id,jdbcType=VARCHAR}
</delete>
<delete id="deleteByExample" parameterType="bz.sunlight.entity.UserExample" >
<!--
WARNING - @mbggenerated
This element is automatically generated by MyBatis Generator, do not modify.
This element was generated on Sat Aug 27 23:42:15 CST 2016.
-->
delete from user
<if test="_parameter != null" >
<include refid="Example_Where_Clause" />
</if>
</delete>
<insert id="insert" parameterType="bz.sunlight.entity.User" >
<!--
WARNING - @mbggenerated
This element is automatically generated by MyBatis Generator, do not modify.
This element was generated on Sat Aug 27 23:42:15 CST 2016.
-->
insert into user (id, name, password
)
values (#{id,jdbcType=VARCHAR}, #{name,jdbcType=VARCHAR}, #{password,jdbcType=VARCHAR}
)
</insert>
<insert id="insertSelective" parameterType="bz.sunlight.entity.User" >
<!--
WARNING - @mbggenerated
This element is automatically generated by MyBatis Generator, do not modify.
This element was generated on Sat Aug 27 23:42:15 CST 2016.
-->
insert into user
<trim prefix="(" suffix=")" suffixOverrides="," >
<if test="id != null" >
id,
</if>
<if test="name != null" >
name,
</if>
<if test="password != null" >
password,
</if>
</trim>
<trim prefix="values (" suffix=")" suffixOverrides="," >
<if test="id != null" >
#{id,jdbcType=VARCHAR},
</if>
<if test="name != null" >
#{name,jdbcType=VARCHAR},
</if>
<if test="password != null" >
#{password,jdbcType=VARCHAR},
</if>
</trim>
</insert>
<select id="countByExample" parameterType="bz.sunlight.entity.UserExample" resultType="java.lang.Integer" >
<!--
WARNING - @mbggenerated
This element is automatically generated by MyBatis Generator, do not modify.
This element was generated on Sat Aug 27 23:42:15 CST 2016.
-->
select count(*) from user
<if test="_parameter != null" >
<include refid="Example_Where_Clause" />
</if>
</select>
<update id="updateByExampleSelective" parameterType="map" >
<!--
WARNING - @mbggenerated
This element is automatically generated by MyBatis Generator, do not modify.
This element was generated on Sat Aug 27 23:42:15 CST 2016.
-->
update user
<set >
<if test="record.id != null" >
id = #{record.id,jdbcType=VARCHAR},
</if>
<if test="record.name != null" >
name = #{record.name,jdbcType=VARCHAR},
</if>
<if test="record.password != null" >
password = #{record.password,jdbcType=VARCHAR},
</if>
</set>
<if test="_parameter != null" >
<include refid="Update_By_Example_Where_Clause" />
</if>
</update>
<update id="updateByExample" parameterType="map" >
<!--
WARNING - @mbggenerated
This element is automatically generated by MyBatis Generator, do not modify.
This element was generated on Sat Aug 27 23:42:15 CST 2016.
-->
update user
set id = #{record.id,jdbcType=VARCHAR},
name = #{record.name,jdbcType=VARCHAR},
password = #{record.password,jdbcType=VARCHAR}
<if test="_parameter != null" >
<include refid="Update_By_Example_Where_Clause" />
</if>
</update>
<update id="updateByPrimaryKeySelective" parameterType="bz.sunlight.entity.User" >
<!--
WARNING - @mbggenerated
This element is automatically generated by MyBatis Generator, do not modify.
This element was generated on Sat Aug 27 23:42:15 CST 2016.
-->
update user
<set >
<if test="name != null" >
name = #{name,jdbcType=VARCHAR},
</if>
<if test="password != null" >
password = #{password,jdbcType=VARCHAR},
</if>
</set>
where id = #{id,jdbcType=VARCHAR}
</update>
<update id="updateByPrimaryKey" parameterType="bz.sunlight.entity.User" >
<!--
WARNING - @mbggenerated
This element is automatically generated by MyBatis Generator, do not modify.
This element was generated on Sat Aug 27 23:42:15 CST 2016.
-->
update user
set name = #{name,jdbcType=VARCHAR},
password = #{password,jdbcType=VARCHAR}
where id = #{id,jdbcType=VARCHAR}
</update>
</mapper>
用這些生成的sql語句基本上可以解決我們單表查詢中的所有情景；而不必我們再去手寫sql(太操蛋了)，是不是有點回到另外一個大框架中了呀;
例如：
我要新增客戶：
那么在service層的代碼就可以這么寫：
@Override
public void saveUser(User record) {
userMapper.insert(record);
}
直接用反向生成的insert方法來進行插入；
你可能會覺得沒什么太多意思：這種sql語句太容易寫了；
那么查詢呢？根據條件查詢，條件比較多得情況下呢？更新，需要動態更新呢？
查詢：
@Override
public List<User> queryUserByName(String name) {
UserExample example=new UserExample();
example.createCriteria().andNameEqualTo(name); //我只需要在這里添加查詢條件即可，添加的查詢條件有很多可供選擇的；Criteria這個對象是不是很熟悉呀！
List<User> users = userMapper.selectByExample(example);
return users;
}
這樣就將根據姓名查詢的服務寫好了，還可以有like,between等多種方法可以供選擇；
更新：
有時候表單提交上來的數據不是很完整，更新需要寫動態sql以防止數據庫的數據被更新成null;
現在我們可以這樣操作：
@Override
public void updateById(User user,String id) {
UserExample example=new UserExample();
example.createCriteria().andIdEqualTo(id);
userMapper.updateByExampleSelective(user, example);
}
動態sql已經反向生成好了，我們只需要將需要更新的條件封裝到example類中即可；
當然，多表關聯暫時還無法這么使用，關於多表關聯可以關注我的另外一篇博文；
這樣，是不是mybatis也實現了全封裝的操作；