mybatis动态SQL语句

原文地址：http://woshixy.blog.51cto.com/5637578/1051311

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

1 2 3 4 5 6 7

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()); }