myibatis查询写法

有些时候,sql语句where条件中,需要一些安全判断,例如按性别检索,如果传入的参数是空的,此时查询出的结果很可能是空的,也许我们需要参数为空时,是查出全部的信息。这是我们可以使用动态sql,增加一个判断,当参数不符合要求的时候,我们可以不去判断此查询条件。
        下文均采用mysql语法和函数(例如字符串链接函数CONCAT)。

        源代码http://limingnihao.javaeye.com/admin/blogs/782190页面最下面;

3.1 if标签
一个很普通的查询:

Xml代码 
<!-- 查询学生list,like姓名 -->  
<select id="getStudentListLikeName" parameterType="StudentEntity" resultMap="studentResultMap">  
    SELECT * from STUDENT_TBL ST    
WHERE ST.STUDENT_NAME LIKE CONCAT(CONCAT('%', #{studentName}),'%')   
</select>  
<!-- 查询学生list,like姓名 -->
<select id="getStudentListLikeName" parameterType="StudentEntity" resultMap="studentResultMap">
SELECT * from STUDENT_TBL ST
WHERE ST.STUDENT_NAME LIKE CONCAT(CONCAT('%', #{studentName}),'%')
</select>

但是此时如果studentName是null或空字符串,此语句很可能报错或查询结果为空。此时我们使用if动态sql语句先进行判断,如果值为null或等于空字符串,我们就不进行此条件的判断。

修改为:

Xml代码 
<!-- 查询学生list,like姓名 -->  
<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>  
<!-- 查询学生list,like姓名 -->
<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>
此时,当studentName的值为null或’’的时候,我们并不进行where条件的判断,所以当studentName值为null或’’值,不附带这个条件,所以查询结果是全部。

由于参数是Java的实体类,所以我们可以把所有条件都附加上,使用时比较灵活, new一个这样的实体类,我们需要限制那个条件,只需要附上相应的值就会where这个条件,相反不去赋值就可以不在where中判断。


   代码中的where标签,请参考3.2.1.

Xml代码 
<!-- 查询学生list,like姓名,=性别、=生日、=班级,使用where,参数entity类型 -->  
<select id="getStudentListWhereEntity" 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>  
        <if test="studentBirthday!=null">  
            AND ST.STUDENT_BIRTHDAY = #{studentBirthday}   
        </if>  
        <if test="classEntity!=null and classEntity.classID !=null and classEntity.classID!='' ">  
            AND ST.CLASS_ID = #{classEntity.classID}   
        </if>  
    </where>  
</select>  
<!-- 查询学生list,like姓名,=性别、=生日、=班级,使用where,参数entity类型 -->
<select id="getStudentListWhereEntity" 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>
  <if test="studentBirthday!=null">
    AND ST.STUDENT_BIRTHDAY = #{studentBirthday}
  </if>
  <if test="classEntity!=null and classEntity.classID !=null and classEntity.classID!='' ">
   AND ST.CLASS_ID = #{classEntity.classID}
  </if>
</where>
</select>
查询,姓名中有‘李’,男,生日在‘1985-05-28’,班级在‘20000002’的学生。

Java代码 
StudentEntity entity = new StudentEntity();   
entity.setStudentName("李");   
entity.setStudentSex("男");   
entity.setStudentBirthday(StringUtil.parse("1985-05-28"));   
entity.setClassEntity(classMapper.getClassByID("20000002"));   
List<StudentEntity> studentList = studentMapper.getStudentListWhereEntity(entity);   
for( StudentEntity entityTemp : studentList){   
    System.out.println(entityTemp.toString());   
}  
StudentEntity entity = new StudentEntity();
entity.setStudentName("李");
entity.setStudentSex("男");
entity.setStudentBirthday(StringUtil.parse("1985-05-28"));
entity.setClassEntity(classMapper.getClassByID("20000002"));
List<StudentEntity> studentList = studentMapper.getStudentListWhereEntity(entity);
for( StudentEntity entityTemp : studentList){
System.out.println(entityTemp.toString());
}

3.2 where、set、trim标签

3.2.1 where
当if标签较多时,这样的组合可能会导致错误。例如,like姓名,等于指定性别等:

Xml代码 
<!-- 查询学生list,like姓名,=性别 -->  
<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>  
</select>  
<!-- 查询学生list,like姓名,=性别 -->
<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>
</select>
如果上面例子,参数studentName为null或’’,则或导致此sql组合成“WHERE AND”之类的关键字多余的错误SQL。
这时我们可以使用where动态语句来解决。这个“where”标签会知道如果它包含的标签中有返回值的话,它就插入一个‘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。
上面例子修改为:

Xml代码 
<!-- 查询学生list,like姓名,=性别 -->  
<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>  
<!-- 查询学生list,like姓名,=性别 -->
<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>

3.2.2 set
当在update语句中使用if标签时,如果前面的if没有执行,则或导致逗号多余错误。使用set标签可以将动态的配置SET 关键字,和剔除追加到条件末尾的任何不相关的逗号。
没有使用if标签时,如果有一个参数为null,都会导致错误,如下示例:

Xml代码 
<!-- 更新学生信息 -->  
<update id="updateStudent" parameterType="StudentEntity">  
    UPDATE STUDENT_TBL   
       SET STUDENT_TBL.STUDENT_NAME = #{studentName},   
           STUDENT_TBL.STUDENT_SEX = #{studentSex},   
           STUDENT_TBL.STUDENT_BIRTHDAY = #{studentBirthday},   
           STUDENT_TBL.CLASS_ID = #{classEntity.classID}   
     WHERE STUDENT_TBL.STUDENT_ID = #{studentID};   
</update>  
<!-- 更新学生信息 -->
<update id="updateStudent" parameterType="StudentEntity">
UPDATE STUDENT_TBL
    SET STUDENT_TBL.STUDENT_NAME = #{studentName},
        STUDENT_TBL.STUDENT_SEX = #{studentSex},
        STUDENT_TBL.STUDENT_BIRTHDAY = #{studentBirthday},
        STUDENT_TBL.CLASS_ID = #{classEntity.classID}
  WHERE STUDENT_TBL.STUDENT_ID = #{studentID};
</update>

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。如下示例:

Xml代码 
<!-- 更新学生信息 -->  
<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>  
<!-- 更新学生信息 -->
<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>
3.2.3 trim
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:

Xml代码 
<!-- 查询学生list,like姓名,=性别 -->  
<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>  
<!-- 查询学生list,like姓名,=性别 -->
<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:

Xml代码 
<!-- 更新学生信息 -->  
<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>  
<!-- 更新学生信息 -->
<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>

3.3 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:

Xml代码 
<!-- 查询学生list,like姓名、或=性别、或=生日、或=班级,使用choose -->  
<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>  
<!-- 查询学生list,like姓名、或=性别、或=生日、或=班级,使用choose -->
<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>
3.4 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。



3.4.1参数为list实例的写法:
SQL写法:

Xml代码 
<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>  
<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>
接口的方法声明:

Java代码 
public List<StudentEntity> getStudentListByClassIDs(List<String> classList);  
public List<StudentEntity> getStudentListByClassIDs(List<String> classList); 测试代码,查询学生中,在20000002、20000003这两个班级的学生:

Java代码 
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());   
}  
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());
}

3.4.2参数为Array实例的写法:
SQL语句:

Xml代码 
<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>  
<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>

接口的方法声明:

Java代码 
public List<StudentEntity> getStudentListByClassIDs(String[] ids);  
public List<StudentEntity> getStudentListByClassIDs(String[] ids);测试代码,查询学生中,在20000002、20000003这两个班级的学生:

Java代码 
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());   
}  


1.<select id="querySysLogList" parameterClass="SystemLogPara" resultMap="SystemLogResult" > 
2.     select  * from ( 
3.            SELECT  
4.          r.*,rownum rn from ( select * from AMS_SYSTEM_LOG t 
5.           <dynamic prepend="where"> 
6.                 <isNotNull prepend="AND" property="userID"> 
7.                      t.UserID like '%$userID$%' 
8.                 </isNotNull> 
9.                <isNotNull prepend="AND" property="userName"> 
10.                      t.UserName like '%$userName$%' 
11.                 </isNotNull> 
12.                 <isNotNull prepend="AND" property="operObjectName"> 
13.                      t.OperObjectName like '%$operObjectName$%' 
14.                 </isNotNull> 
15.                  <isNotNull prepend="AND" property="theModule"> 
16.                      t.TheModule like '%$theModule$%' 
17.                 </isNotNull> 
18.                  <isNotNull prepend="AND" property="userIP"> 
19.                      t.UserIP like '%$userIP$%' 
20.                 </isNotNull> 
21.                 <isNotNull prepend="AND" property="operResult"> 
22.                    OperResult like '%$operResult$%' 
23.                 </isNotNull> 
24.                 <isNotNull prepend="AND" property="beginTime"> 
25.                     t.OperTime >= #beginTime# 
26.                 </isNotNull> 
27.                  <isNotNull prepend="AND" property="endTime"> 
28.                     <![CDATA[
29.                     t.OperTime <= #endTime#
30.                      ]]> 
31.                 </isNotNull> 
32.                 <isNotNull prepend="AND" property="userGroupList"> 
33.                    <iterate property="userGroupList" open="(" close=")" conjunction="OR"> 
34.           t.userGroupKey like '%$userGroupList[]$%' 
35.                    </iterate> 
36.                 </isNotNull> 
37.             </dynamic> 
38.             order by t.OperTime desc 
39.             ) r 
40.               <![CDATA[
41.            
42.        ) s  where s.rn <= #endRowNum# and  s.rn >=#startRowNum# 
43.      ]]> 
44.             
45.  </select> 

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