646      阿裏雲  技術社區[雲棲]

mybatis動態SQL語句

一 if標簽

<select 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標簽

<select 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>

如果它包含的標簽中有返回值的話就插入一個where。此外如果標簽返回的內容是以AND或OR開頭的，則它會剔除掉。

三 set 標簽

使用set+if標簽修改後，如果某項為null則不進行更新，而是保持數據庫原值

<update 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標簽

trim是更靈活的去處多餘關鍵字的標簽，他可以實踐where和set的效果。

where例子的等效trim語句

<select 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語句

<update 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)

有時候並不想應用所有的條件，而隻是想從多個選項中選擇一個。MyBatis提供了choose 元素，按順序判斷when中的條件出否成立，如果有一個成立，則choose結束。當choose中所有when的條件都不滿則時，則執行otherwise中的sql。類似於Java 的switch語句，choose為switch，when為case，otherwise則為default。

<select 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

對於動態SQL 非常必須的，主是要迭代一個集合，通常是用於IN 條件。List實例將使用“list”做為鍵，數組實例以“array”做為鍵。

1 參數為list實例的寫法

SqlMapper.xml
<select 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 參數為Array實例的寫法

SqlMapper.xml
<select 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:https://blog.csdn.net/ask_rent/article/details/6320326

最後更新：2017-04-03 05:40:29

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