mybatis 动态SQL语句
MyBatis学习 之 一、MyBatis简介与配置MyBatis+Spring+MySql
MyBatis学习 之 二、SQL语句映射文件(1)resultMap
MyBatis学习 之 二、SQL语句映射文件(2)增删改查、参数、缓存
MyBatis学习 之 三、动态SQL语句
MyBatis学习 之 四、MyBatis配置文件
有些时候，sql语句where条件中，需要一些安全判断，例如按某一条件查询时如果传入的参数是空，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。使用Oracle的序列、mysql的函数生成Id。这时我们可以使用动态sql。
下文均采用mysql语法和函数（例如字符串链接函数CONCAT）。
3.1 selectKey 标签
在insert语句中，在Oracle经常使用序列、在MySQL中使用函数来自动生成插入表的主键，而且需要方法能返回这个生成主键。使用myBatis的selectKey标签可以实现这个效果。
下面例子，使用mysql数据库自定义函数nextval('student')，用来生成一个key，并把他设置到传入的实体类中的studentId属性上。所以在执行完此方法后，边可以通过这个实体类获取生成的key。
<pre name="code" class="java"><!-- 插入学生 自动主键-->
<insert id="createStudentAutoKey" parameterType="liming.student.manager.data.model.StudentEntity" keyProperty="studentId">
<selectKey keyProperty="studentId" resultType="String" order="BEFORE">
select nextval('student')
</selectKey>
INSERT INTO STUDENT_TBL(STUDENT_ID,
STUDENT_NAME,
STUDENT_SEX,
STUDENT_BIRTHDAY,
STUDENT_PHOTO,
CLASS_ID,
PLACE_ID)
VALUES (#{studentId},
#{studentName},
#{studentSex},
#{studentBirthday},
#{studentPhoto, javaType=byte[], jdbcType=BLOB, typeHandler=org.apache.ibatis.type.BlobTypeHandler},
#{classId},
#{placeId})
</insert>
<!-- 插入学生 自动主键-->
<insert id="createStudentAutoKey" parameterType="liming.student.manager.data.model.StudentEntity" keyProperty="studentId">
<selectKey keyProperty="studentId" resultType="String" order="BEFORE">select nextval('student')</selectKey>
INSERT INTO STUDENT_TBL(STUDENT_ID,STUDENT_NAME,STUDENT_SEX,STUDENT_BIRTHDAY,STUDENT_PHOTO,CLASS_ID,PLACE_ID) VALUES (#{studentId},#{studentName},#{studentSex},#{studentBirthday},#{studentPhoto, javaType=byte[], jdbcType=BLOB, typeHandler=org.apache.ibatis.type.BlobTypeHandler},#{classId},#{placeId})
</insert>
调用接口方法，和获取自动生成key
StudentEntity entity = new StudentEntity();
entity.setStudentName("黎明你好");
entity.setStudentSex(1);
entity.setStudentBirthday(DateUtil.parse("1985-05-28"));
entity.setClassId("20000001");
entity.setPlaceId("70000001");
this.dynamicSqlMapper.createStudentAutoKey(entity);
System.out.println("新增学生ID: " + entity.getStudentId());
StudentEntity entity = new StudentEntity();
entity.setStudentName("黎明你好");
entity.setStudentSex(1);
entity.setStudentBirthday(DateUtil.parse("1985-05-28"));
entity.setClassId("20000001");
entity.setPlaceId("70000001");
this.dynamicSqlMapper.createStudentAutoKey(entity);
System.out.println("新增学生ID: " + entity.getStudentId());
selectKey语句属性配置细节：
| 属性 | 描述 | 取值 |
| keyProperty | selectKey 语句生成结果需要设置的属性。 | |
| resultType | 生成结果类型，MyBatis 允许使用基本的数据类型，包括String 、int类型。 | |
| order | 1：BEFORE，会先选择主键，然后设置keyProperty，再执行insert语句； 2：AFTER，就先运行insert 语句再运行selectKey 语句。 |
BEFORE AFTER |
| statementType | MyBatis 支持STATEMENT，PREPARED和CALLABLE 的语句形式， 对应Statement ，PreparedStatement 和CallableStatement 响应 | STATEMENT PREPARED CALLABLE |
3.2 if标签
if标签可用在许多类型的sql语句中，我们以查询为例。首先看一个很普通的查询：
<!-- 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或studentSex为null，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，增加灵活性。
参数为实体类StudentEntity。将实体类中所有的属性均进行判断，如果不为空则执行判断条件。
<pre name="code" class="java"><!-- 2 if(判断参数) - 将实体类不为空的属性作为where条件 -->
<select id="getStudentList_if" resultMap="resultMap_studentEntity" parameterType="liming.student.manager.data.model.StudentEntity">
SELECT ST.STUDENT_ID,
ST.STUDENT_NAME,
ST.STUDENT_SEX,
ST.STUDENT_BIRTHDAY,
ST.STUDENT_PHOTO,
ST.CLASS_ID,
ST.PLACE_ID
FROM STUDENT_TBL ST
WHERE
<if test="studentName !=null ">
ST.STUDENT_NAME LIKE CONCAT(CONCAT('%', #{studentName, jdbcType=VARCHAR}),'%')
</if>
<if test="studentSex != null and studentSex != '' ">
AND ST.STUDENT_SEX = #{studentSex, jdbcType=INTEGER}
</if>
<if test="studentBirthday != null ">
AND ST.STUDENT_BIRTHDAY = #{studentBirthday, jdbcType=DATE}
</if>
<if test="classId != null and classId!= '' ">
AND ST.CLASS_ID = #{classId, jdbcType=VARCHAR}
</if>
<if test="classEntity != null and classEntity.classId !=null and classEntity.classId !=' ' ">
AND ST.CLASS_ID = #{classEntity.classId, jdbcType=VARCHAR}
</if>
<if test="placeId != null and placeId != '' ">
AND ST.PLACE_ID = #{placeId, jdbcType=VARCHAR}
</if>
<if test="placeEntity != null and placeEntity.placeId != null and placeEntity.placeId != '' ">
AND ST.PLACE_ID = #{placeEntity.placeId, jdbcType=VARCHAR}
</if>
<if test="studentId != null and studentId != '' ">
AND ST.STUDENT_ID = #{studentId, jdbcType=VARCHAR}
</if>
</select>
<!-- 2 if(判断参数) - 将实体类不为空的属性作为where条件 -->
<select id="getStudentList_if" resultMap="resultMap_studentEntity" parameterType="liming.student.manager.data.model.StudentEntity">
SELECT ST.STUDENT_ID,ST.STUDENT_NAME,ST.STUDENT_SEX, ST.STUDENT_BIRTHDAY,ST.STUDENT_PHOTO,ST.CLASS_ID, ST.PLACE_ID FROM STUDENT_TBL ST WHERE
<if test="studentName !=null ">
ST.STUDENT_NAME LIKE CONCAT(CONCAT('%', #{studentName, jdbcType=VARCHAR}),'%')
</if>
<if test="studentSex != null and studentSex != '' ">
AND ST.STUDENT_SEX = #{studentSex, jdbcType=INTEGER}
</if>
<if test="studentBirthday != null ">
AND ST.STUDENT_BIRTHDAY = #{studentBirthday, jdbcType=DATE}
</if>
<if test="classId != null and classId!= '' ">
AND ST.CLASS_ID = #{classId, jdbcType=VARCHAR}
</if>
<if test="classEntity != null and classEntity.classId !=null and classEntity.classId !=' ' ">
AND ST.CLASS_ID = #{classEntity.classId, jdbcType=VARCHAR}
</if>
<if test="placeId != null and placeId != '' ">
AND ST.PLACE_ID = #{placeId, jdbcType=VARCHAR}
</if>
<if test="placeEntity != null and placeEntity.placeId != null and placeEntity.placeId != '' ">
AND ST.PLACE_ID = #{placeEntity.placeId, jdbcType=VARCHAR}
</if>
<if test="studentId != null and studentId != '' ">
AND ST.STUDENT_ID = #{studentId, jdbcType=VARCHAR}
</if>
</select>
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。
<pre name="code" class="java">public void select_test_2_1() {
StudentEntity entity = new StudentEntity();
entity.setStudentName("");
entity.setStudentSex(1);
entity.setStudentBirthday(DateUtil.parse("1985-05-28"));
entity.setClassId("20000001");
//entity.setPlaceId("70000001");
List<StudentEntity> list = this.dynamicSqlMapper.getStudentList_if(entity);
for (StudentEntity e : list) {
System.out.println(e.toString());
}
}
public void select_test_2_1() {
StudentEntity entity = new StudentEntity();
entity.setStudentName("");
entity.setStudentSex(1);
entity.setStudentBirthday(DateUtil.parse("1985-05-28"));
entity.setClassId("20000001");
//entity.setPlaceId("70000001");
List<StudentEntity> list = this.dynamicSqlMapper.getStudentList_if(entity);
for (StudentEntity e : list) {
System.out.println(e.toString());
}
}
3.3 if + where 的条件判断
当where中的条件使用的if标签较多时，这样的组合可能会导致错误。我们以在3.1中的查询语句为例子，当java代码按如下方法调用时：
<pre name="code" class="java">@Test
public void select_test_2_1() {
StudentEntity entity = new StudentEntity();
entity.setStudentName(null);
entity.setStudentSex(1);
List<StudentEntity> list = this.dynamicSqlMapper.getStudentList_if(entity);
for (StudentEntity e : list) {
System.out.println(e.toString());
}
}
@Testpublic void select_test_2_1() {
StudentEntity entity = new StudentEntity();
entity.setStudentName(null);
entity.setStudentSex(1);
List<StudentEntity> list = this.dynamicSqlMapper.getStudentList_if(entity);
for (StudentEntity e : list) {
System.out.println(e.toString());
}
}
如果上面例子，参数studentName为null，将不会进行STUDENT_NAME列的判断，则会直接导“WHERE AND”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：
<pre name="code" class="java"><!-- 3 select - where/if(判断参数) - 将实体类不为空的属性作为where条件 -->
<select id="getStudentList_whereIf" resultMap="resultMap_studentEntity" parameterType="liming.student.manager.data.model.StudentEntity">
SELECT ST.STUDENT_ID,
ST.STUDENT_NAME,
ST.STUDENT_SEX,
ST.STUDENT_BIRTHDAY,
ST.STUDENT_PHOTO,
ST.CLASS_ID,
ST.PLACE_ID
FROM STUDENT_TBL ST
<where>
<if test="studentName !=null ">
ST.STUDENT_NAME LIKE CONCAT(CONCAT('%', #{studentName, jdbcType=VARCHAR}),'%')
</if>
<if test="studentSex != null and studentSex != '' ">
AND ST.STUDENT_SEX = #{studentSex, jdbcType=INTEGER}
</if>
<if test="studentBirthday != null ">
AND ST.STUDENT_BIRTHDAY = #{studentBirthday, jdbcType=DATE}
</if>
<if test="classId != null and classId!= '' ">
AND ST.CLASS_ID = #{classId, jdbcType=VARCHAR}
</if>
<if test="classEntity != null and classEntity.classId !=null and classEntity.classId !=' ' ">
AND ST.CLASS_ID = #{classEntity.classId, jdbcType=VARCHAR}
</if>
<if test="placeId != null and placeId != '' ">
AND ST.PLACE_ID = #{placeId, jdbcType=VARCHAR}
</if>
<if test="placeEntity != null and placeEntity.placeId != null and placeEntity.placeId != '' ">
AND ST.PLACE_ID = #{placeEntity.placeId, jdbcType=VARCHAR}
</if>
<if test="studentId != null and studentId != '' ">
AND ST.STUDENT_ID = #{studentId, jdbcType=VARCHAR}
</if>
</where>
</select>
<!-- 3 select - where/if(判断参数) - 将实体类不为空的属性作为where条件 -->
<select id="getStudentList_whereIf" resultMap="resultMap_studentEntity" parameterType="liming.student.manager.data.model.StudentEntity">
SELECT ST.STUDENT_ID, ST.STUDENT_NAME, ST.STUDENT_SEX, ST.STUDENT_BIRTHDAY, ST.STUDENT_PHOTO, ST.CLASS_ID,ST.PLACE_ID
FROM STUDENT_TBL ST
<where>
<if test="studentName !=null ">
ST.STUDENT_NAME LIKE CONCAT(CONCAT('%', #{studentName, jdbcType=VARCHAR}),'%')
</if>
<if test="studentSex != null and studentSex != '' ">
AND ST.STUDENT_SEX = #{studentSex, jdbcType=INTEGER}
</if>
<if test="studentBirthday != null ">
AND ST.STUDENT_BIRTHDAY = #{studentBirthday, jdbcType=DATE}
</if>
<if test="classId != null and classId!= '' ">
AND ST.CLASS_ID = #{classId, jdbcType=VARCHAR}
</if>
<if test="classEntity != null and classEntity.classId !=null and classEntity.classId !=' ' ">
AND ST.CLASS_ID = #{classEntity.classId, jdbcType=VARCHAR}
</if>
<if test="placeId != null and placeId != '' ">
AND ST.PLACE_ID = #{placeId, jdbcType=VARCHAR}
</if>
<if test="placeEntity != null and placeEntity.placeId != null and placeEntity.placeId != '' ">
AND ST.PLACE_ID = #{placeEntity.placeId, jdbcType=VARCHAR}
</if>
<if test="studentId != null and studentId != '' ">
AND ST.STUDENT_ID = #{studentId, jdbcType=VARCHAR}
</if>
</where>
</select>
3.4 if + set 的更新语句
当update语句中没有使用if标签时，如果有一个参数为null，都会导致错误。
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。
使用if+set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：
<!-- 4 if/set(判断参数) - 将实体类不为空的属性更新 -->
<update id="updateStudent_if_set" parameterType="liming.student.manager.data.model.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="studentPhoto != null ">
STUDENT_TBL.STUDENT_PHOTO = #{studentPhoto, javaType=byte[], jdbcType=BLOB, typeHandler=org.apache.ibatis.type.BlobTypeHandler},
</if>
<if test="classId != '' ">
STUDENT_TBL.CLASS_ID = #{classId}
</if>
<if test="placeId != '' ">
STUDENT_TBL.PLACE_ID = #{placeId}
</if>
</set>
WHERE STUDENT_TBL.STUDENT_ID = #{studentId};
</update>
<!-- 4 if/set(判断参数) - 将实体类不为空的属性更新 -->
<update id="updateStudent_if_set" parameterType="liming.student.manager.data.model.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="studentPhoto != null ">
STUDENT_TBL.STUDENT_PHOTO = #{studentPhoto, javaType=byte[], jdbcType=BLOB, typeHandler=org.apache.ibatis.type.BlobTypeHandler}, </if>
<if test="classId != '' ">
STUDENT_TBL.CLASS_ID = #{classId}
</if>
<if test="placeId != '' ">
STUDENT_TBL.PLACE_ID = #{placeId}
</if>
</set>
WHERE STUDENT_TBL.STUDENT_ID = #{studentId};
</update>
3.5 if + trim代替where/set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。
3.5.1trim代替where
<pre name="code" class="java"><!-- 5.1 if/trim代替where(判断参数) - 将实体类不为空的属性作为where条件 -->
<select id="getStudentList_if_trim" resultMap="resultMap_studentEntity">
SELECT ST.STUDENT_ID,
ST.STUDENT_NAME,
ST.STUDENT_SEX,
ST.STUDENT_BIRTHDAY,
ST.STUDENT_PHOTO,
ST.CLASS_ID,
ST.PLACE_ID
FROM STUDENT_TBL ST
<trim prefix="WHERE" prefixOverrides="AND|OR">
<if test="studentName !=null ">
ST.STUDENT_NAME LIKE CONCAT(CONCAT('%', #{studentName, jdbcType=VARCHAR}),'%')
</if>
<if test="studentSex != null and studentSex != '' ">
AND ST.STUDENT_SEX = #{studentSex, jdbcType=INTEGER}
</if>
<if test="studentBirthday != null ">
AND ST.STUDENT_BIRTHDAY = #{studentBirthday, jdbcType=DATE}
</if>
<if test="classId != null and classId!= '' ">
AND ST.CLASS_ID = #{classId, jdbcType=VARCHAR}
</if>
<if test="classEntity != null and classEntity.classId !=null and classEntity.classId !=' ' ">
AND ST.CLASS_ID = #{classEntity.classId, jdbcType=VARCHAR}
</if>
<if test="placeId != null and placeId != '' ">
AND ST.PLACE_ID = #{placeId, jdbcType=VARCHAR}
</if>
<if test="placeEntity != null and placeEntity.placeId != null and placeEntity.placeId != '' ">
AND ST.PLACE_ID = #{placeEntity.placeId, jdbcType=VARCHAR}
</if>
<if test="studentId != null and studentId != '' ">
AND ST.STUDENT_ID = #{studentId, jdbcType=VARCHAR}
</if>
</trim>
</select>
<!-- 5.1 if/trim代替where(判断参数) - 将实体类不为空的属性作为where条件 -->
<select id="getStudentList_if_trim" resultMap="resultMap_studentEntity">
SELECT ST.STUDENT_ID, ST.STUDENT_NAME, ST.STUDENT_SEX, ST.STUDENT_BIRTHDAY, ST.STUDENT_PHOTO, ST.CLASS_ID, ST.PLACE_ID
FROM STUDENT_TBL ST
<trim prefix="WHERE" prefixOverrides="AND|OR">
<if test="studentName !=null ">
ST.STUDENT_NAME LIKE CONCAT(CONCAT('%', #{studentName, jdbcType=VARCHAR}),'%')
</if>
<if test="studentSex != null and studentSex != '' ">
AND ST.STUDENT_SEX = #{studentSex, jdbcType=INTEGER}
</if>
<if test="studentBirthday != null ">
AND ST.STUDENT_BIRTHDAY = #{studentBirthday, jdbcType=DATE}
</if>
<if test="classId != null and classId!= '' ">
AND ST.CLASS_ID = #{classId, jdbcType=VARCHAR}
</if>
<if test="classEntity != null and classEntity.classId !=null and classEntity.classId !=' ' ">
AND ST.CLASS_ID = #{classEntity.classId, jdbcType=VARCHAR}
</if>
<if test="placeId != null and placeId != '' ">
AND ST.PLACE_ID = #{placeId, jdbcType=VARCHAR}
</if>
<if test="placeEntity != null and placeEntity.placeId != null and placeEntity.placeId != '' ">
AND ST.PLACE_ID = #{placeEntity.placeId, jdbcType=VARCHAR}
</if>
<if test="studentId != null and studentId != '' ">
AND ST.STUDENT_ID = #{studentId, jdbcType=VARCHAR}
</if>
</trim>
</select>
3.5.2 trim代替set
<pre name="code" class="java"><!-- 5.2 if/trim代替set(判断参数) - 将实体类不为空的属性更新 -->
<update id="updateStudent_if_trim" parameterType="liming.student.manager.data.model.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="studentPhoto != null ">
STUDENT_TBL.STUDENT_PHOTO = #{studentPhoto, javaType=byte[], jdbcType=BLOB, typeHandler=org.apache.ibatis.type.BlobTypeHandler},
</if>
<if test="classId != '' ">
STUDENT_TBL.CLASS_ID = #{classId},
</if>
<if test="placeId != '' ">
STUDENT_TBL.PLACE_ID = #{placeId}
</if>
</trim>
WHERE STUDENT_TBL.STUDENT_ID = #{studentId}
</update>
<!-- 5.2 if/trim代替set(判断参数) - 将实体类不为空的属性更新 -->
<update id="updateStudent_if_trim" parameterType="liming.student.manager.data.model.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="studentPhoto != null ">
STUDENT_TBL.STUDENT_PHOTO = #{studentPhoto, javaType=byte[], jdbcType=BLOB, typeHandler=org.apache.ibatis.type.BlobTypeHandler}, </if>
<if test="classId != '' ">
STUDENT_TBL.CLASS_ID = #{classId},
</if>
<if test="placeId != '' ">
STUDENT_TBL.PLACE_ID = #{placeId}
</if>
</trim>
WHERE STUDENT_TBL.STUDENT_ID = #{studentId}
</update>
3.6 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。而使用if标签时，只要test中的表达式为true，就会执行if标签中的条件。MyBatis提供了choose 元素。if标签是与(and)的关系，而choose比傲天是或（or）的关系。
choose标签是按顺序判断其内部when标签中的test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。
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。choose会从上到下选择一个when标签的test为true的sql执行。安全考虑，我们使用where将choose包起来，放置关键字多于错误。
<pre name="code" class="java"><!-- 6 choose(判断参数) - 按顺序将实体类第一个不为空的属性作为where条件 -->
<select id="getStudentList_choose" resultMap="resultMap_studentEntity" parameterType="liming.student.manager.data.model.StudentEntity">
SELECT ST.STUDENT_ID,
ST.STUDENT_NAME,
ST.STUDENT_SEX,
ST.STUDENT_BIRTHDAY,
ST.STUDENT_PHOTO,
ST.CLASS_ID,
ST.PLACE_ID
FROM STUDENT_TBL ST
<where>
<choose>
<when test="studentName !=null ">
ST.STUDENT_NAME LIKE CONCAT(CONCAT('%', #{studentName, jdbcType=VARCHAR}),'%')
</when >
<when test="studentSex != null and studentSex != '' ">
AND ST.STUDENT_SEX = #{studentSex, jdbcType=INTEGER}
</when >
<when test="studentBirthday != null ">
AND ST.STUDENT_BIRTHDAY = #{studentBirthday, jdbcType=DATE}
</when >
<when test="classId != null and classId!= '' ">
AND ST.CLASS_ID = #{classId, jdbcType=VARCHAR}
</when >
<when test="classEntity != null and classEntity.classId !=null and classEntity.classId !=' ' ">
AND ST.CLASS_ID = #{classEntity.classId, jdbcType=VARCHAR}
</when >
<when test="placeId != null and placeId != '' ">
AND ST.PLACE_ID = #{placeId, jdbcType=VARCHAR}
</when >
<when test="placeEntity != null and placeEntity.placeId != null and placeEntity.placeId != '' ">
AND ST.PLACE_ID = #{placeEntity.placeId, jdbcType=VARCHAR}
</when >
<when test="studentId != null and studentId != '' ">
AND ST.STUDENT_ID = #{studentId, jdbcType=VARCHAR}
</when >
<otherwise>
</otherwise>
</choose>
</where>
</select>
<!-- 6 choose(判断参数) - 按顺序将实体类第一个不为空的属性作为where条件 -->
<select id="getStudentList_choose" resultMap="resultMap_studentEntity" parameterType="liming.student.manager.data.model.StudentEntity">
SELECT ST.STUDENT_ID, ST.STUDENT_NAME, ST.STUDENT_SEX, ST.STUDENT_BIRTHDAY, ST.STUDENT_PHOTO, ST.CLASS_ID, ST.PLACE_ID
FROM STUDENT_TBL ST
<where>
<choose>
<when test="studentName !=null ">
ST.STUDENT_NAME LIKE CONCAT(CONCAT('%', #{studentName, jdbcType=VARCHAR}),'%')
</when >
<when test="studentSex != null and studentSex != '' ">
AND ST.STUDENT_SEX = #{studentSex, jdbcType=INTEGER}
</when >
<when test="studentBirthday != null ">
AND ST.STUDENT_BIRTHDAY = #{studentBirthday, jdbcType=DATE}
</when >
<when test="classId != null and classId!= '' ">
AND ST.CLASS_ID = #{classId, jdbcType=VARCHAR}
</when >
<when test="classEntity != null and classEntity.classId !=null and classEntity.classId !=' ' ">
AND ST.CLASS_ID = #{classEntity.classId, jdbcType=VARCHAR}
</when >
<when test="placeId != null and placeId != '' ">
AND ST.PLACE_ID = #{placeId, jdbcType=VARCHAR}
</when >
<when test="placeEntity != null and placeEntity.placeId != null and placeEntity.placeId != '' ">
AND ST.PLACE_ID = #{placeEntity.placeId, jdbcType=VARCHAR}
</when >
<when test="studentId != null and studentId != '' ">
AND ST.STUDENT_ID = #{studentId, jdbcType=VARCHAR}
</when >
<otherwise>
</otherwise>
</choose>
</where>
</select>
3.7 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。
foreach元素是非常强大的，它允许你指定一个集合，声明集合项和索引变量，它们可以用在元素体内。它也允许你指定开放和关闭的字符串，在迭代之间放置分隔符。这个元素是很智能的，它不会偶然地附加多余的分隔符。
注意：你可以传递一个List实例或者数组作为参数对象传给MyBatis。当你这么做的时候，MyBatis会自动将它包装在一个Map中，用名称在作为键。List实例将会以“list”作为键，而数组实例将会以“array”作为键。
这个部分是对关于XML配置文件和XML映射文件的而讨论的。下一部分将详细讨论Java API，所以你可以得到你已经创建的最有效的映射。
3.7.1参数为array示例的写法
接口的方法声明：
<pre name="code" class="java">public List<StudentEntity> getStudentListByClassIds_foreach_array(String[] classIds); public List<StudentEntity> getStudentListByClassIds_foreach_array(String[] classIds);
动态SQL语句：
<pre name="code" class="java"><!— 7.1 foreach(循环array参数) - 作为where中in的条件 -->
<select id="getStudentListByClassIds_foreach_array" resultMap="resultMap_studentEntity">
SELECT ST.STUDENT_ID,
ST.STUDENT_NAME,
ST.STUDENT_SEX,
ST.STUDENT_BIRTHDAY,
ST.STUDENT_PHOTO,
ST.CLASS_ID,
ST.PLACE_ID
FROM STUDENT_TBL ST
WHERE ST.CLASS_ID IN
<foreach collection="array" item="classIds" open="(" separator="," close=")">
#{classIds}
</foreach>
</select>
<!— 7.1 foreach(循环array参数) - 作为where中in的条件 -->
<select id="getStudentListByClassIds_foreach_array" resultMap="resultMap_studentEntity">
SELECT ST.STUDENT_ID, ST.STUDENT_NAME, ST.STUDENT_SEX, ST.STUDENT_BIRTHDAY, ST.STUDENT_PHOTO, ST.CLASS_ID, ST.PLACE_ID FROM STUDENT_TBL ST
WHERE ST.CLASS_ID IN
<foreach collection="array" item="classIds" open="(" separator="," close=")">
#{classIds}
</foreach>
</select>
测试代码，查询学生中，在20000001、20000002这两个班级的学生：
<pre name="code" class="java">@Test
public void test7_foreach() {
String[] classIds = { "20000001", "20000002" };
List<StudentEntity> list = this.dynamicSqlMapper.getStudentListByClassIds_foreach_array(classIds);
for (StudentEntity e : list) {
System.out.println(e.toString());
}
@Testpublic void test7_foreach() {
String[] classIds = { "20000001", "20000002" };
List<StudentEntity> list = this.dynamicSqlMapper.getStudentListByClassIds_foreach_array(classIds);
for (StudentEntity e : list) {
System.out.println(e.toString());
}
}
3.7.2参数为list示例的写法
接口的方法声明：
public List<StudentEntity> getStudentListByClassIds_foreach_list(List<String> classIdList); public List<StudentEntity> getStudentListByClassIds_foreach_list(List<String> classIdList);
动态SQL语句：
<!-- 7.2 foreach(循环List<String>参数) - 作为where中in的条件 -->
<select id="getStudentListByClassIds_foreach_list" resultMap="resultMap_studentEntity">
SELECT ST.STUDENT_ID,
ST.STUDENT_NAME,
ST.STUDENT_SEX,
ST.STUDENT_BIRTHDAY,
ST.STUDENT_PHOTO,
ST.CLASS_ID,
ST.PLACE_ID
FROM STUDENT_TBL ST
WHERE ST.CLASS_ID IN
<foreach collection="list" item="classIdList" open="(" separator="," close=")">
#{classIdList}
</foreach>
</select>
<!-- 7.2 foreach(循环List<String>参数) - 作为where中in的条件 -->
<select id="getStudentListByClassIds_foreach_list" resultMap="resultMap_studentEntity">
SELECT ST.STUDENT_ID, ST.STUDENT_NAME, ST.STUDENT_SEX, ST.STUDENT_BIRTHDAY, ST.STUDENT_PHOTO, ST.CLASS_ID, ST.PLACE_ID FROM STUDENT_TBL ST
WHERE ST.CLASS_ID IN
<foreach collection="list" item="classIdList" open="(" separator="," close=")">
#{classIdList}
</foreach>
</select>
测试代码，查询学生中，在20000001、20000002这两个班级的学生：
@Test
public void test7_2_foreach() {
ArrayList<String> classIdList = new ArrayList<String>();
classIdList.add("20000001");
classIdList.add("20000002");
List<StudentEntity> list = this.dynamicSqlMapper.getStudentListByClassIds_foreach_list(classIdList);
for (StudentEntity e : list) {
System.out.println(e.toString());
}
}
@Testpublic void test7_2_foreach() {
ArrayList<String> classIdList = new ArrayList<String>();
classIdList.add("20000001");
classIdList.add("20000002");
List<StudentEntity> list = this.dynamicSqlMapper.getStudentListByClassIds_foreach_list(classIdList);
for (StudentEntity e : list) {
System.out.println(e.toString());
}
}