一 if标签
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<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
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<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
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<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
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<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
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<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。
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<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
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<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
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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
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<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> |
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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());} |