Mybatis(五):动态SQL
- 前言
- 一、if
- 二、where
- 三、trim
- 四、choose、when、otherwise
- 五、foreach
- 1. 示例一
- 2. 示例二
- 六、SQL片段
前言
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Mybatis
框架的动态SQL技术是一种根据特定条件动态拼装SQL
语句的功能,它存在的意义是为了解决拼接SQL
语句字符串时的痛点问题。
动态SQL:
⭕
if
:根据标签中test属性所对应的表达式决定标签中的内容是否需要拼接到SQL中
⭕
where
:● 当
where
标签中有内容时,会自动生成where
关键字,并且将内容前多余的and
或or
去掉
● 当where
标签中没有内容时,此时where
标签没有任何效果
注意:where
标签不能将其中内容后面多余的and
或or
去掉
⭕
trim
:
● 若标签中有内容时:
prefix
|suffix
:将trim标签中内容前面或后面添加指定内容suffixOverrides
|prefixOverrides
:将trim标签中内容前面或后面去掉指定内容● 若标签中没有内容时,
trim
标签也没有任何效果
⭕
choose
、when
、otherwise
● 相当于if...else if...else
●when
至少要有一个,otherwise
最多只能有一个
⭕
foreach
●
collection
:设置需要循环的数组或集合
●item
:表示数组或集合中的每一个数据
●separator
:循环体之间的分割符
●open
:foreach
标签所循环的所有内容的开始符
●close
:foreach
标签所循环的所有内容的结束符
⭕
sql
标签
● 设置SQL
片段:eid,emp_name,age,sex,email
● 引用SQL
片段:
一、if
if
标签可通过test
属性的表达式进行判断,若表达式的结果为true
,则标签中的内容会执行;反之标签中的内容不会执行
DynamicSQLMapper
/** * @description:多条件查询 * @author: Hey * @date: 2022/7/4 13:13 * @param: [emp] * @return: java.util.List **/List<Emp> getEmpByCondition(Emp emp);
DynamicSQLMapper.xml
<select id="getEmpByConditionOne" resultType="Emp">select * from t_emp where 1=1<if test="empName != null and empName != ''">emp_name = #{empName}</if><if test="age != null and age != ''">and age = #{age}</if><if test="sex != null and sex != ''">and sex = #{sex}</if><if test="email != null and email != ''">and email = #{email}</if></select>
DynamicSQLMapperTest
/** * @description:测试if标签 * @author: Hey* @date: 2022/7/4 13:25 * @param: [] * @return: void **/@Testpublic void testGetEmpByCondition(){SqlSession sqlSession = SqlSessionUtils.getSqlSession();DynamicSQLMapper mapper = sqlSession.getMapper(DynamicSQLMapper.class);List<Emp> list = mapper.getEmpByCondition(new Emp(null, "", null, "", null));System.out.println(list);}
二、where
DynamicSQLMapper.xml
<select id="getEmpByConditionTwo" resultType="Emp">select * from t_emp<where><if test="empName != null and empName != ''">emp_name = #{empName}</if><if test="age != null and age != ''">and age = #{age}</if><if test="sex != null and sex != ''">or sex = #{sex}</if><if test="email != null and email != ''">and email = #{email}</if></where></select>
DynamicSQLMapperTest
/** * @description:测试where标签 * @author: Hey* @date: 2022/7/4 13:25 * @param: [] * @return: void **/@Testpublic void testGetEmpByCondition(){SqlSession sqlSession = SqlSessionUtils.getSqlSession();DynamicSQLMapper mapper = sqlSession.getMapper(DynamicSQLMapper.class);List<Emp> list = mapper.getEmpByCondition(new Emp(null, "", null, "", null));System.out.println(list);}
三、trim
DynamicSQLMapper.xml
<select id="getEmpByCondition" resultType="Emp">select <include refid="empColumns"></include> from t_emp<trim prefix="where" suffixOverrides="and|or"><if test="empName != null and empName != ''">emp_name = #{empName} and</if><if test="age != null and age != ''">age = #{age} or</if><if test="sex != null and sex != ''">sex = #{sex} and</if><if test="email != null and email != ''">email = #{email}</if></trim></select>
四、choose、when、otherwise
DeptMapper
/** * @description:测试choose、when、otherwise * @author: Hey* @date: 2022/7/4 16:50 * @param: [emp] * @return: java.util.List **/List<Emp> getEmpByChoose(Emp emp);
DynamicSQLMapper.xml:
<!--List getEmpByChoose(Emp emp);--><select id="getEmpByChoose" resultType="Emp">select * from t_emp<where><choose><when test="empName != null and empName != ''">emp_name = #{empName}</when><when test="age != null and age != ''">age = #{age}</when><when test="sex != null and sex != ''">sex = #{sex}</when><when test="email != null and email != ''">email = #{email}</when><otherwise>did = 1</otherwise></choose></where></select><sql id="empColumns">eid,emp_name,age,sex,email</sql><!--List getEmpByCondition(Emp emp);-->
五、foreach
1. 示例一
DynamicSQLMapper
/** * @description:通过数组实现批量删除 * @author: Hey * @date: 2022/7/4 17:03 * @param: [eids] * @return: int **/int deleteMoreByArray(@Param("eids") Integer[] eids);
DynamicSQLMapper.xml
<delete id="deleteMoreByArray">delete from t_emp where<foreach collection="eids" item="eid" separator="or">eid = #{eid}</foreach><!--delete from t_emp where eid in#{eid}--></delete>
DynamicSQLMapperTest
/** * @description:通过数组实现批量删除 * @author: Hey * @date: 2022/7/4 17:11 * @param: [] * @return: void **/@Testpublic void testDeleteMoreByArray(){SqlSession sqlSession = SqlSessionUtils.getSqlSession();DynamicSQLMapper mapper = sqlSession.getMapper(DynamicSQLMapper.class);int result = mapper.deleteMoreByArray(new Integer[]{6, 7, 8});System.out.println(result);}
2. 示例二
DynamicSQLMapper
/** * @description:通过list集合实现批量添加 * @author: Hey * @date: 2022/7/4 17:23 * @param: [emps] * @return: int **/int insertMoreByList(@Param("emps") List<Emp> emps);
DynamicSQLMapper.xml
<!--int insertMoreByList(@Param("emps") List emps);--><insert id="insertMoreByList">insert into t_emp values<foreach collection="emps" item="emp" separator=",">(null,#{emp.empName},#{emp.age},#{emp.sex},#{emp.email},null)</foreach></insert>
DynamicSQLMapperTest
/** * @description:通过list集合实现批量添加 * @author: Hey * @date: 2022/7/4 17:24 * @param: [] * @return: void **/@Testpublic void testInsertMoreByList(){SqlSession sqlSession = SqlSessionUtils.getSqlSession();DynamicSQLMapper mapper = sqlSession.getMapper(DynamicSQLMapper.class);Emp emp1 = new Emp(null,"a1",23,"男","123@qq.com");Emp emp2 = new Emp(null,"a2",23,"男","123@qq.com");Emp emp3 = new Emp(null,"a3",23,"男","123@qq.com");List<Emp> emps = Arrays.asList(emp1, emp2, emp3);System.out.println(mapper.insertMoreByList(emps));}
属性:
collection:设置要循环的数组或集合
item:表示集合或数组中的每一个数据
separator:设置循环体之间的分隔符
open:设置foreach标签中的内容的开始符
close:设置foreach标签中的内容的结束符
六、SQL片段
<sql id="empColumns"> eid,ename,age,sex,did</sql>select <include refid="empColumns"></include> from t_emp