MyBatis总结之动态SQL

版权声明：@AaronFo https://blog.csdn.net/sinat_33212645/article/details/85126120

目录

1.if

2.choose(when、otherwise)

3.where

4.set

5.foreach

6.bind

---

1.if

 1.1 条件查询，如参数非空则执行条件：

<select id="getByUserName" parameterType="string" resultMap="sysUserResultMap">
       SELECT * FROM sys_user T
	    <where>
		    <if test="_parameter  !=null and _parameter  !='' ">
		    USER_NAME = #{value}
		    </if>
	    </where>
    </select>

2.choose(when、otherwise)

 2.1 有时我们不想应用到所有的条件语句，而只想从中择其一项。针对这种情况，MyBatis 提供了 choose 元素，它有点像 Java 中的 switch 语句。如根据用户名和身份证查询，两者非空则根据状态查询：

    <select id="getByUserCnNameOrIdCard" parameterType = "SysUser" resultMap = "sysUserResultMap">
	    SELECT * FROM sys_user T WHERE 1=1
	    <choose>
	       <when test="userCnName != null and userCnName !='' ">
	          AND USER_CN_NAME like CONCAT('%','${userCnName}','%')
	       </when>
	       <when test="idCard !=null and idCard != '' ">
	          AND IDCARD = #{idCard}
	       </when>
	       <otherwise>
	          AND STATUS = 2     
	       </otherwise>
	    </choose>
    </select>

3.where

    <select id="getByUuid" parameterType="string" resultMap="sysUserResultMap">
       SELECT * FROM sys_user T
	    <where>
		    <if test="_parameter  !=null and _parameter  !='' ">
		    UUID = #{value}
		    </if>
	    </where>
    </select>

4.set

 4.1 动态包含需要更新的列而摄取其他的，如更新用户信息操作：

    <update id="edit"  parameterType = "SysUser">
        UPDATE sys_user 
        <set>
	        <if test="userName !=null and userName !='' ">
	           USER_NAME = #{userName}
	        </if>
	        <if test="password !=null and password !='' ">
	           PASSWORD = #{password}
	        </if>
	        <if test="userCnName !=null and userCnName !='' ">
	           USER_CN_NAME = #{userCnName}
	        </if>
	        <if test="idCard !=null and idCard !='' ">
	           IDCARD = #{idCard}
	        </if>
	        <if test="phone !=null and phone !='' ">
	           PHONE = #{phone}
	        </if>
	        <if test="email !=null and email !='' ">
	           EMAIL = #{email}
	        </if>
	        <if test="imageUrl !=null and imageUrl !='' ">
	           IMAGE_URL = #{imageUrl}
	        </if>
	        <if test="address !=null and address !='' ">
	           ADDRESS = #{address}
	        </if>
	        <if test="status !=null and status !='' ">
	           STATUS = #{status}
	        </if>
	        <if test="createTime !=null and createTime !='' ">
	           CREATE_TIME = #{createTime}
	        </if>
        </set>
       WHERE UUID = #{uuid}
    </update>

5.foreach

 5.1动态 SQL 的另外一个常用的操作需求是对一个集合进行遍历，通常是在构建 IN 条件语句的时候，如根据id集合查询多用户：

    <select id="getUsersByIdList" parameterType = "list" resultMap = "sysUserResultMap">
       SELECT * FROM sys_user WHERE UUID IN 
       <foreach collection="list" item = "item" index = "index" 
           open="(" separator = "," close = ")" >
          #{item}
       </foreach>
    </select>

6.bind

 6.1 bind 元素可以从 OGNL 表达式中创建一个变量并将其绑定到上下文，如模糊查询：

<select id="selectUserLike" parameterType="SysUser" resultType="SysUser">
  <bind name="pattern" value="'%' + userName + '%'" />
  SELECT * FROM sys_user
  WHERE USER_NAME LIKE #{pattern}
</select>