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());

}



原帖地址:http://blog.csdn.net/ask_rent/article/details/6320326