MyBatis学习笔记(五) 动态SQL

最新推荐文章于 2025-05-19 21:09:00 发布

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#Mybatis #动态SQL

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本文详细解析了MyBatis中各种条件查询的使用方法，包括if、choose、when、otherwise、where、trim、foreach和set等元素的运用，通过具体的代码示例展示了如何根据不同的业务需求构建动态SQL，实现高效的数据检索。

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if条件

StudentMapper.java

public List<Student> searchStudents(Map<String,Object> map);

StudentMapper.xml

<select id="searchStudents" parameterType="Map" resultMap="StudentResult">
    select * from t_student 
    where gradeId=#{gradeId}
    <if test="name!=null">
        and name like #{name}
    </if>
    <if test="age!=null">
        and age=#{age}
    </if>
</select>

StudentTest.java

@Test
public void testSearchStudents() {
	logger.info("查询学生(带条件)");
	Map<String,Object> map=new HashMap<String,Object>();
	map.put("gradeId", 2);
	map.put("name", "%李%");
	map.put("age", 11);
	List<Student> studentList=studentMapper.searchStudents(map);
	for(Student student:studentList){
		System.out.println(student);
	}
}

choose，when和otherwise条件

StudentMapper.java

public List<Student> searchStudents2(Map<String,Object> map);

StudentMapper.xml

<select id="searchStudents2" parameterType="Map" resultMap="StudentResult">
    select * from t_student 
    <choose>
 	<when test="searchBy=='gradeId'">
 		where gradeId=#{gradeId}
 	</when>
 	<when test="searchBy=='name'">
 		where name like #{name}
 	</when>
 	<otherwise>
 		where age=#{age}
 	</otherwise>
    </choose>
</select>

StudentTest.java

@Test
public void testSearchStudents2() {
	logger.info("查询学生(带条件)");
	Map<String,Object> map=new HashMap<String,Object>();
	map.put("searchBy", "age");
	map.put("gradeId", 2);
	map.put("name", "%李%");
	map.put("age", 11);
	List<Student> studentList=studentMapper.searchStudents2(map);
	for(Student student:studentList){
	    System.out.println(student);
	}
}

where条件

1，自动加上 where；

2，如果 where 子句以 and 或者 or 开头，则自动删除第一个 and 或者 or

StudentMapper.java新增searchStudents3方法、

StudentTest.java同if条件的StudentTest.java、

StudentMapper.xml

<select id="searchStudents3" parameterType="Map" resultMap="StudentResult">
	select * from t_student 
	<where>
		<if test="gradeId!=null">
			where gradeId=#{gradeId}
		</if>
		<if test="name!=null">
			and name like #{name}
		</if>
		<if test="age!=null">
			and age=#{age}
		</if>
	</where>
</select>

trim条件

功能和 where 元素类似，提供了前缀，后缀功能，更加灵活；

StudentMapper.xml

<select id="searchStudents4" parameterType="Map" resultMap="StudentResult">
	select * from t_student 
	 <trim prefix="where" prefixOverrides="and|or">
		 <if test="gradeId!=null">
		 	gradeId=#{gradeId}
		 </if>
		 <if test="name!=null">
		 	and name like #{name}
		 </if>
		 <if test="age!=null">
		 	and age=#{age}
		 </if>
	 </trim>
</select>

foreach循环

StudentMapper.xml

<select id="searchStudents5" parameterType="Map" resultMap="StudentResult">
    select * from t_student 
    <if test="gradeIds!=null">
        <where>
            gradeId in 
            <foreach item="gradeId" collection="gradeIds" open="(" separator="," close=")">
	        #{gradeId}
            </foreach>
        </where>
    </if>
</select>

StudentTest.java

@Test
public void testSearchStudents5() {
	logger.info("查询学生(带条件)");
	Map<String,Object> map=new HashMap<String,Object>();
	List<Integer> gradeIds=new ArrayList<Integer>();
	// gradeIds.add(1);
	gradeIds.add(2);
	map.put("gradeIds", gradeIds);
	List<Student> studentList=studentMapper.searchStudents5(map);
	for(Student student:studentList){
		System.out.println(student);
	}
}

set条件

StudentMapper.java

public int updateStudent(Student student);

StudentMapper.xml

<update id="updateStudent" parameterType="Student">
	update t_student
	<set>
	 <if test="name!=null">
	 	name=#{name},
	 </if>
	 <if test="age!=null">
	 	age=#{age},
	 </if>
	</set>
	where id=#{id}
</update>

StudentTest.java

@Test
public void testUpdateStudent(){
	logger.info("更新学生(带条件)");
	Student student=new Student();
	student.setId(1);
	student.setName("张三3");
	student.setAge(13);
	studentMapper.updateStudent(student);
	sqlSession.commit();
}