mybatis动态SQL语句

た入场券 2022-08-07 10:58 357阅读 0赞

一 if标签

<span style="font-family:KaiTi_GB2312;font-size:18px;"><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></span>

二 where标签

<span style="font-family:KaiTi_GB2312;font-size:18px;"><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></span>

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

<span style="font-family:KaiTi_GB2312;font-size:18px;"><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></span>

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

<span style="font-family:KaiTi_GB2312;font-size:18px;"><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></span>

set例子的等效trim语句

<span style="font-family:KaiTi_GB2312;font-size:18px;"><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></span>

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。

<span style="font-family:KaiTi_GB2312;font-size:18px;"><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></span>

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

<span style="font-family:KaiTi_GB2312;font-size:18px;"><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></span>

Java

<span style="font-family:KaiTi_GB2312;font-size:18px;">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());
    }</span>

2 参数为Array实例的写法

SqlMapper.xml

<span style="font-family:KaiTi_GB2312;font-size:18px;"><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></span>

Java

<span style="font-family:KaiTi_GB2312;font-size:18px;">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());
    }</span>

choose (when, otherwise)  
         有时候我们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。  
         if是与(and)的关系，而choose是或（or）的关系。

例如下面例子，同样把所有可以限制的条件都写上，方面使用。选择条件顺序，when标签的从上到下的书写顺序：

<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>