mybatis动态SQL语句

 

一 if标签

<select id=" getStudentListLikeName " parameterType="StudentEntity" resultMap="studentResultMap">  SELECT * from STUDENT_TBL ST  <if test="studentName!=null and studentName!='' ">   WHERE ST.STUDENT_NAME LIKE CONCAT(CONCAT('%', #{studentName}),'%')  </if> </select>

 

 

二 where标签

<select id="getStudentListWhere" parameterType="StudentEntity" resultMap="studentResultMap">  SELECT * from STUDENT_TBL ST  <where>   <if test="studentName!=null and studentName!='' ">    ST.STUDENT_NAME LIKE CONCAT(CONCAT('%', #{studentName}),'%')   </if>   <if test="studentSex!= null and studentSex!= '' ">    AND ST.STUDENT_SEX = #{studentSex}   </if>  </where> </select>

如果它包含的标签中有返回值的话就插入一个where。此外如果标签返回的内容是以AND或OR开头的，则它会剔除掉。

 

三 set 标签

使用set+if标签修改后，如果某项为null则不进行更新，而是保持数据库原值

<update id="updateStudent" parameterType="StudentEntity">  UPDATE STUDENT_TBL  <set>   <if test="studentName!=null and studentName!='' ">    STUDENT_TBL.STUDENT_NAME = #{studentName},   </if>   <if test="studentSex!=null and studentSex!='' ">    STUDENT_TBL.STUDENT_SEX = #{studentSex},   </if>   <if test="studentBirthday!=null ">    STUDENT_TBL.STUDENT_BIRTHDAY = #{studentBirthday},   </if>   <if test="classEntity!=null and classEntity.classID!=null and classEntity.classID!='' ">    STUDENT_TBL.CLASS_ID = #{classEntity.classID}   </if>  </set>  WHERE STUDENT_TBL.STUDENT_ID = #{studentID}; </update>

 

四 trim标签

 

trim是更灵活的去处多余关键字的标签，他可以实践where和set的效果。

where例子的等效trim语句

<select id="getStudentListWhere" parameterType="StudentEntity" resultMap="studentResultMap">  SELECT * from STUDENT_TBL ST  <trim prefix="WHERE" prefixOverrides="AND|OR">   <if test="studentName!=null and studentName!='' ">    ST.STUDENT_NAME LIKE CONCAT(CONCAT('%', #{studentName}),'%')   </if>   <if test="studentSex!= null and studentSex!= '' ">    AND ST.STUDENT_SEX = #{studentSex}   </if>  </trim> </select>

 

set例子的等效trim语句

<update id="updateStudent" parameterType="StudentEntity">  UPDATE STUDENT_TBL  <trim prefix="SET" suffixOverrides=",">   <if test="studentName!=null and studentName!='' ">    STUDENT_TBL.STUDENT_NAME = #{studentName},   </if>   <if test="studentSex!=null and studentSex!='' ">    STUDENT_TBL.STUDENT_SEX = #{studentSex},   </if>   <if test="studentBirthday!=null ">    STUDENT_TBL.STUDENT_BIRTHDAY = #{studentBirthday},   </if>   <if test="classEntity!=null and classEntity.classID!=null and classEntity.classID!='' ">    STUDENT_TBL.CLASS_ID = #{classEntity.classID}   </if>  </trim>  WHERE STUDENT_TBL.STUDENT_ID = #{studentID}; </update>

 

 

五 choose (when, otherwise)

有时候并不想应用所有的条件，而只是想从多个选项中选择一个。MyBatis提供了choose 元素，按顺序判断when中的条件出否成立，如果有一个成立，则choose结束。当choose中所有when的条件都不满则时，则执行otherwise中的sql。类似于Java 的switch语句，choose为switch，when为case，otherwise则为default。

 

<select id="getStudentListChooseEntity" parameterType="StudentEntity" resultMap="studentResultMap">  SELECT * from STUDENT_TBL ST  <where>   <choose>    <when test="studentName!=null and studentName!='' ">     ST.STUDENT_NAME LIKE CONCAT(CONCAT('%', #{studentName}),'%')    </when>    <when test="studentSex!= null and studentSex!= '' ">     AND ST.STUDENT_SEX = #{studentSex}    </when>    <when test="studentBirthday!=null">     AND ST.STUDENT_BIRTHDAY = #{studentBirthday}    </when>    <when test="classEntity!=null and classEntity.classID !=null and classEntity.classID!='' ">     AND ST.CLASS_ID = #{classEntity.classID}    </when>    <otherwise></otherwise>   </choose>  </where> </select>

 

 

六 foreach

对于动态SQL 非常必须的，主是要迭代一个集合，通常是用于IN 条件。List实例将使用“list”做为键，数组实例以“array”做为键。

1 参数为list实例的写法

SqlMapper.xml <select id="getStudentListByClassIDs" resultMap="studentResultMap">  SELECT * FROM STUDENT_TBL ST   WHERE ST.CLASS_ID IN    <foreach collection="list" item="classList"  open="(" separator="," close=")">    #{classList}   </foreach>  </select>

Java List<String> classList = new ArrayList<String>(); classList.add("20000002"); classList.add("20000003"); List<StudentEntity> studentList = studentMapper.getStudentListByClassIDs(classList); for(StudentEntity entityTemp : studentList){  System.out.println(entityTemp.toString()); }

 

 

 

2 参数为Array实例的写法

SqlMapper.xml <select id="getStudentListByClassIDs" resultMap="studentResultMap">  SELECT * FROM STUDENT_TBL ST   WHERE ST.CLASS_ID IN    <foreach collection="array" item="ids"  open="(" separator="," close=")">    #{ids}   </foreach> </select>

 

Java String[] ids = new String[2]; ids[0] = "20000002"; ids[1] = "20000003"; List<StudentEntity> studentList = studentMapper.getStudentListByClassIDs(ids); for(StudentEntity entityTemp : studentList){  System.out.println(entityTemp.toString()); }