MyBatis 动态 SQL-阿里云开发者社区

MyBatis通过 OGNL 来进行动态 SQL 的使用的。目前，动态 SQL 支持以下几种标签：

元素	作用	备注
if	判断语句	单条件分支
choose(when、otherwise)	相当于Java中的if else	多条件分支
trim(where、set)	辅助元素	用于处理SQL拼接问题
foreach	循环语句	批量插入、更新、查询
bind	创建一个变量，并绑定到上下文中	用于兼容不同数据库，防止SQL注入等

创建数据库和表

DROP TABLE IF EXISTS `student`;
CREATE TABLE `student` (
  `student_id` int(10) unsigned NOT NULL AUTO_INCREMENT COMMENT '编号',
  `name` varchar(20) DEFAULT NULL COMMENT '姓名',
  `phone` varchar(20) DEFAULT NULL COMMENT '电话',
  `email` varchar(50) DEFAULT NULL COMMENT '邮箱',
  `sex` tinyint(4) DEFAULT NULL COMMENT '性别',
  `locked` tinyint(4) DEFAULT NULL COMMENT '状态(0:正常,1:锁定)',
  `gmt_created` datetime DEFAULT CURRENT_TIMESTAMP COMMENT '存入数据库的时间',
  `gmt_modified` datetime DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP COMMENT '修改的时间',
  `delete` int(11) DEFAULT NULL,
  PRIMARY KEY (`student_id`)
) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci COMMENT='学生表';

接口函数

/**
 * 根据输入的学生信息进行条件检索
 * 1. 当只输入用户名时， 使用用户名进行模糊检索；
 * 2. 当只输入邮箱时， 使用性别进行完全匹配
 * 3. 当用户名和性别都存在时， 用这两个条件进行查询匹配的用
 * @param student
 * @return
 */
List<Student> selectByStudentSelective(Student student);

/**
 * 更新非空属性
 */
int updateByPrimaryKeySelective(Student record);

/**
 * 非空字段才进行插入
 */
int insertSelective(Student record);

/**
 * - 当 studen_id 有值时， 使用 studen_id 进行查询；
 * - 当 studen_id 没有值时， 使用 name 进行查询；
 * - 否则返回空
 */
Student selectByIdOrName(Student record);

/**
 * 根据输入的学生信息进行条件检索
 * 1. 当只输入用户名时， 使用用户名进行模糊检索；
 * 2. 当只输入邮箱时， 使用性别进行完全匹配
 * 3. 当用户名和性别都存在时， 用这两个条件进行查询匹配的用
 */
List<Student> selectByStudentSelectiveWhereTag(Student student);

/**
 * 获取 id 集合中的用户信息
 * @param ids
 * @return
 */
List<Student> selectByStudentIdList(List<Integer> ids);

/**
 * 批量插入学生
 */
int insertList(List<Student> students);

if 标签

<!--在 WHERE 条件中使用 if 标签-->
<select id="selectByStudentSelective" resultMap="BaseResultMap" parameterType="com.homejim.mybatis.entity.Student">
  select
  <include refid="Base_Column_List" />
  from student
  where 1=1
  <if test="name != null and name !=''">
    and name like concat('%', #{name}, '%')
  </if>
  <if test="sex != null">
    and sex=#{sex}
  </if>
</select>

<!--UPDATE 更新列中使用 if 标签-->
<update id="updateByPrimaryKeySelective" parameterType="com.homejim.mybatis.entity.Student">
update student
<set>
  <if test="name != null">
    `name` = #{name,jdbcType=VARCHAR},
  </if>
  <if test="phone != null">
    phone = #{phone,jdbcType=VARCHAR},
  </if>
  <if test="email != null">
    email = #{email,jdbcType=VARCHAR},
  </if>
  <if test="sex != null">
    sex = #{sex,jdbcType=TINYINT},
  </if>
  <if test="locked != null">
    locked = #{locked,jdbcType=TINYINT},
  </if>
  <if test="gmtCreated != null">
    gmt_created = #{gmtCreated,jdbcType=TIMESTAMP},
  </if>
  <if test="gmtModified != null">
    gmt_modified = #{gmtModified,jdbcType=TIMESTAMP},
  </if>
</set>
where student_id = #{studentId,jdbcType=INTEGER}

<!--INSERT 动态插入中使用 if 标签-->
<insert id="insertSelective" parameterType="com.homejim.mybatis.entity.Student">
   insert into student
   <trim prefix="(" suffix=")" suffixOverrides=",">
     <if test="studentId != null">
       student_id,
     </if>
     <if test="name != null">
       `name`,
     </if>
     <if test="phone != null">
       phone,
     </if>
     <if test="email != null">
       email,
     </if>
     <if test="sex != null">
       sex,
     </if>
     <if test="locked != null">
       locked,
     </if>
     <if test="gmtCreated != null">
       gmt_created,
     </if>
     <if test="gmtModified != null">
       gmt_modified,
     </if>
   </trim>
   <trim prefix="values (" suffix=")" suffixOverrides=",">
     <if test="studentId != null">
       #{studentId,jdbcType=INTEGER},
     </if>
     <if test="name != null">
       #{name,jdbcType=VARCHAR},
     </if>
     <if test="phone != null">
       #{phone,jdbcType=VARCHAR},
     </if>
     <if test="email != null">
       #{email,jdbcType=VARCHAR},
     </if>
     <if test="sex != null">
       #{sex,jdbcType=TINYINT},
     </if>
     <if test="locked != null">
       #{locked,jdbcType=TINYINT},
     </if>
     <if test="gmtCreated != null">
       #{gmtCreated,jdbcType=TIMESTAMP},
     </if>
     <if test="gmtModified != null">
       #{gmtModified,jdbcType=TIMESTAMP},
     </if>
   </trim>
 </insert>

choose 标签

<select id="selectByIdOrName" resultMap="BaseResultMap" parameterType="com.homejim.mybatis.entity.Student">
    select
    <include refid="Base_Column_List" />
    from student
    where 1=1
    <choose>
      <when test="studentId != null">
        and student_id=#{studentId}
      </when>
      <when test="name != null and name != ''">
        and name=#{name}
      </when>
      <otherwise>
        and 1=2
      </otherwise>
    </choose>
  </select>

trim(set、where)

<select id="selectByStudentSelectiveWhereTag" resultMap="BaseResultMap" parameterType="com.homejim.mybatis.entity.Student">
   select
   <include refid="Base_Column_List" />
   from student
  <where>
   <if test="name != null and name !=''">
     and name like concat('%', #{name}, '%')
   </if>
   <if test="sex != null">
     and sex=#{sex}
   </if>
  </where>
 </select>

<!--trim 来表示 where-->
<trim prefix="where" prefixOverrides="AND |OR">
</trim>

<!--trim 来表示 set-->
<trim prefix="SET" suffixOverrides=",">
</trim>

prefix: 当 trim 元素包含有内容时，增加 prefix 所指定的前缀

prefixOverrides: 当 trim 元素包含有内容时，去除 prefixOverrides 指定的前缀

suffix: 当 trim 元素包含有内容时，增加 suffix 所指定的后缀

suffixOverrides：当 trim 元素包含有内容时，去除 suffixOverrides 指定的后缀

foreach 标签

collection: 必填，集合/数组/Map的名称.

item: 变量名。即从迭代的对象中取出的每一个值

index: 索引的属性名。当迭代的对象为 Map 时，该值为 Map 中的 Key.

open: 循环开头的字符串

close: 循环结束的字符串

separator: 每次循环的分隔符

多参数请使用 @Param 来指定参数的名称，如果参数是Map指定为 Map 中的对应的 Key 即可。其实上面的 @Param 最后也是转化为 Map 的。

<!--在 where 中使用 foreach-->
<select id="selectByStudentIdList" resultMap="BaseResultMap">
  select
  <include refid="Base_Column_List" />
  from student
  where student_id in
  <foreach collection="list" item="id" open="(" close=")" separator="," index="i">
    #{id}
  </foreach>
</select>

<!--foreach 实现批量插入-->
<insert id="insertList">
  insert into student(name, phone, email, sex, locked)
  values
  <foreach collection="list" item="student" separator=",">
    (
    #{student.name}, #{student.phone},#{student.email},
    #{student.sex},#{student.locked}
    )
  </foreach>
</insert>

bind 标签
bind 标签是通过 OGNL 表达式去定义一个上下文的变量，这样方便我们使用。

<if test="name != null and name !=''">
  and name like concat('%', #{name}, '%')
</if>

在 MySQL 中，该函数支持多参数，但在 Oracle 中只支持两个参数。那么我们可以使用 bind 来让该 SQL 达到支持两个数据库的作用

<if test="name != null and name !=''">
     <bind name="nameLike" value="'%'+name+'%'"/>
     and name like #{nameLike}
</if>

测试

@Test
public void selectByStudent() {
   SqlSession sqlSession = null;
   sqlSession = sqlSessionFactory.openSession();
   StudentMapper studentMapper = sqlSession.getMapper(StudentMapper.class);
   Student search = new Student();
   search.setName("明");
   System.out.println("只有名字时的查询");
   List<Student> studentsByName = studentMapper.selectByStudentSelective(search);
   for (int i = 0; i < studentsByName.size(); i++) {
       System.out.println(ToStringBuilder.reflectionToString(studentsByName.get(i), ToStringStyle.MULTI_LINE_STYLE));
   }
   search.setName(null);
   search.setSex((byte) 1);
   System.out.println("只有性别时的查询");
   List<Student> studentsBySex = studentMapper.selectByStudentSelective(search);
   for (int i = 0; i < studentsBySex.size(); i++) {
       System.out.println(ToStringBuilder.reflectionToString(studentsBySex.get(i), ToStringStyle.MULTI_LINE_STYLE));
   }
   System.out.println("姓名和性别同时存在的查询");
   search.setName("明");
   List<Student> studentsByNameAndSex = studentMapper.selectByStudentSelective(search);
   for (int i = 0; i < studentsByNameAndSex.size(); i++) {
       System.out.println(ToStringBuilder.reflectionToString(studentsByNameAndSex.get(i), ToStringStyle.MULTI_LINE_STYLE));
   }
   sqlSession.commit();
   sqlSession.close();
}

@Test
public void updateByStudentSelective() {
    SqlSession sqlSession = null;
    sqlSession = sqlSessionFactory.openSession();
    StudentMapper studentMapper = sqlSession.getMapper(StudentMapper.class);
    Student student = new Student();
    student.setStudentId(1);
    student.setName("明明");
    student.setPhone("13838438888");
    System.out.println(studentMapper.updateByPrimaryKeySelective(student));
    sqlSession.commit();
    sqlSession.close();
}

@Test
public void insertByStudentSelective() {
    SqlSession sqlSession = null;
    sqlSession = sqlSessionFactory.openSession();
    StudentMapper studentMapper = sqlSession.getMapper(StudentMapper.class);
    Student student = new Student();
    student.setName("小飞机");
    student.setPhone("13838438899");
    student.setEmail("xiaofeiji@qq.com");
    student.setLocked((byte) 0);
    System.out.println(studentMapper.insertSelective(student));
    sqlSession.commit();
    sqlSession.close();
}

@Test
public void selectByIdOrName() {
    SqlSession sqlSession = null;
    sqlSession = sqlSessionFactory.openSession();
    StudentMapper studentMapper = sqlSession.getMapper(StudentMapper.class);
    Student student = new Student();
    student.setName("小飞机");
    student.setStudentId(1);
    Student studentById = studentMapper.selectByIdOrName(student);
    System.out.println("有 ID 则根据 ID 获取");
    System.out.println(ToStringBuilder.reflectionToString(studentById, ToStringStyle.MULTI_LINE_STYLE));
    student.setStudentId(null);
    Student studentByName = studentMapper.selectByIdOrName(student);
    System.out.println("没有 ID 则根据 name 获取");
    System.out.println(ToStringBuilder.reflectionToString(studentByName, ToStringStyle.MULTI_LINE_STYLE));
    student.setName(null);
    Student studentNull = studentMapper.selectByIdOrName(student);
    System.out.println("没有 ID 和 name, 返回 null");
    Assert.assertNull(studentNull);
    sqlSession.commit();
    sqlSession.close();
}

@Test
public void selectByStudentWhereTag() {
    SqlSession sqlSession = null;
    sqlSession = sqlSessionFactory.openSession();
    StudentMapper studentMapper = sqlSession.getMapper(StudentMapper.class);
    Student search = new Student();
    search.setName("明");
    System.out.println("只有名字时的查询");
    List<Student> studentsByName = studentMapper.selectByStudentSelectiveWhereTag(search);
    for (int i = 0; i < studentsByName.size(); i++) {
        System.out.println(ToStringBuilder.reflectionToString(studentsByName.get(i), ToStringStyle.MULTI_LINE_STYLE));
    }
    search.setSex((byte) 1);
    System.out.println("姓名和性别同时存在的查询");
    List<Student> studentsBySex = studentMapper.selectByStudentSelectiveWhereTag(search);
    for (int i = 0; i < studentsBySex.size(); i++) {
        System.out.println(ToStringBuilder.reflectionToString(studentsBySex.get(i), ToStringStyle.MULTI_LINE_STYLE));
    }
    System.out.println("姓名和性别都不存在时查询");
    search.setName(null);
    search.setSex(null);
    List<Student> studentsByNameAndSex = studentMapper.selectByStudentSelectiveWhereTag(search);
    for (int i = 0; i < studentsByNameAndSex.size(); i++) {
        System.out.println(ToStringBuilder.reflectionToString(studentsByNameAndSex.get(i), ToStringStyle.MULTI_LINE_STYLE));
    }
    sqlSession.commit();
    sqlSession.close();
}

@Test
public void selectByStudentIdList() {
    SqlSession sqlSession = null;
    sqlSession = sqlSessionFactory.openSession();
    StudentMapper studentMapper = sqlSession.getMapper(StudentMapper.class);
    List<Integer> ids = new LinkedList<>();
    ids.add(1);
    ids.add(3);
    List<Student> students = studentMapper.selectByStudentIdList(ids);
    for (int i = 0; i < students.size(); i++) {
        System.out.println(ToStringBuilder.reflectionToString(students.get(i), ToStringStyle.MULTI_LINE_STYLE));
    }
    sqlSession.commit();
    sqlSession.close();
}

@Test
public void insertList() {
    SqlSession sqlSession = null;
    sqlSession = sqlSessionFactory.openSession();
    StudentMapper studentMapper = sqlSession.getMapper(StudentMapper.class);
    List<Student> students = new LinkedList<>();
    Student stu1 = new Student();
    stu1.setName("批量01");
    stu1.setPhone("13888888881");
    stu1.setLocked((byte) 0);
    stu1.setEmail("13888888881@138.com");
    stu1.setSex((byte) 1);
    students.add(stu1);
    Student stu2 = new Student();
    stu2.setName("批量02");
    stu2.setPhone("13888888882");
    stu2.setLocked((byte) 0);
    stu2.setEmail("13888888882@138.com");
    stu2.setSex((byte) 0);
    students.add(stu2);
    System.out.println(studentMapper.insertList(students));
    sqlSession.commit();
    sqlSession.close();
}

MyBatis 动态 SQL

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