Java SSM框架之MyBatis3MyBatis之动态SQL
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前言:
mybatis框架中最具特色的便是sql语句中的自定义,而动态sql的使用又使整个框架更加灵活。
创建User表
/*Table structure for table `user` */ DROP TABLE IF EXISTS `user`; CREATE TABLE `user` ( `id` bigint(20) unsigned NOT NULL AUTO_INCREMENT, `name` varchar(20) NOT NULL, `username` varchar(20) NOT NULL, `age` int(3) NOT NULL, `phone` varchar(11) NOT NULL, `email` varchar(50) NOT NULL, PRIMARY KEY (`id`) ) ENGINE=InnoDB AUTO_INCREMENT=4 DEFAULT CHARSET=utf8; /*Data for the table `user` */ insert into `user`(`id`,`name`,`username`,`age`,`phone`,`email`) values (1,\'张三\',\'zs\',18,\'15010998046\',\'4567899@qq.com\'),(2,\'李四\',\'ls\',19,\'15019087600\',\'567657642@qq.com\'),(3,\'王五\',\'ww\',20,\'15010898065\',\'2323248@qq.com\'); /*!40101 SET SQL_MODE=@OLD_SQL_MODE */; /*!40014 SET FOREIGN_KEY_CHECKS=@OLD_FOREIGN_KEY_CHECKS */; /*!40014 SET UNIQUE_CHECKS=@OLD_UNIQUE_CHECKS */; /*!40111 SET SQL_NOTES=@OLD_SQL_NOTES */;
标签 | 作用 |
if | 单条件分支,相当于判断语句 |
choose、when、otherwise | 多条件分支,相当于Java中的switch语句 |
set、where、trim | 辅助条件判断,用于拼接语句 |
foreach | 集合进行遍历(尤其是在构建 IN 条件语句的时候) |
bind | 创建一个变量,并将其绑定到当前的上下文 |
if标签
User实体
package cn.cnki.ref.pojo; public class User { private int id; private String name; private String username; private int age; private String phone; private String email; //无参构造函数必须有,ORM框架调用的就是无参构造函数 public User() { } public User(int id, String name, String username, int age, String phone, String email) { super(); this.id = id; this.name = name; this.username = username; this.age = age; this.phone = phone; this.email = email; } public int getId() { return id; } public void setId(int id) { this.id = id; } public String getName() { return name; } public void setName(String name) { this.name = name; } public String getUsername() { return username; } public void setUsername(String username) { this.username = username; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } public String getPhone() { return phone; } public void setPhone(String phone) { this.phone = phone; } public String getEmail() { return email; } public void setEmail(String email) { this.email = email; } @Override public String toString() { return "User [id=" + id + ", name=" + name + ", username=" + username + ", age=" + age + ", phone=" + phone + ", email=" + email + "]"; } }
UserMapper
package cn.cnki.ref.mapper; import cn.cnki.ref.pojo.User; import java.util.List; public interface UserMapper { public List<User> getUser(User user); }
UserMapper.xml
<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" > <!--用户mapper关系映射 --> <mapper namespace="cn.cnki.ref.mapper.UserMapper"> <select id="getUser" resultType="cn.cnki.ref.pojo.User"> select * from user where 1=1 <if test="id != null">and id=#{id}</if> <if test="age != null">and age=#{age}</if> <if test="name != null">and name=#{name}</if> </select> </mapper>
UserController
package cn.cnki.ref.controller; import cn.cnki.ref.mapper.UserMapper; import cn.cnki.ref.pojo.User; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.web.bind.annotation.GetMapping; import org.springframework.web.bind.annotation.RestController; import java.util.List; @RestController public class UserController { @Autowired private UserMapper UserMapper; @GetMapping("/getUser") public List<User> getUser() { User user = new User(1, "张三", null, 18, null, null); List<User> users = UserMapper.getUser(user); System.out.println(users); return users; } }
测试
http://localhost:8080/getUser
choose (when, otherwise)标签
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。
<!-- choose(判断参数) - 按顺序将实体类 User 第一个不为空的属性作为:where条件 --> <select id="getUserList_choose" resultMap="resultMap_user" parameterType="com.yiibai.pojo.User"> SELECT * FROM User u <where> <choose> <when test="username !=null "> u.username LIKE CONCAT(CONCAT(\'%\', #{username, jdbcType=VARCHAR}),\'%\') </when > <when test="sex != null and sex != \'\' "> AND u.sex = #{sex, jdbcType=INTEGER} </when > <when test="birthday != null "> AND u.birthday = #{birthday, jdbcType=DATE} </when > <otherwise> </otherwise> </choose> </where> </select>
where标签
<select id="getUser" resultType="cn.cnki.ref.pojo.User"> select * from user <where> <if test="id != null">and id=#{id} </if> <if test="age != null">and age=#{age} </if> <if test="name != null">and name=#{name}</if> </where> </select>
输出sql语句
trim标签
<select id="getUser" resultType="cn.cnki.ref.pojo.User"> select * from user <trim prefix="where" suffixOverrides="and"> <if test="id != null">id=#{id} and</if> <if test="age != null">age=#{age} and</if> <if test="name != null">name=#{name} and</if> </trim> </select>
trim标签下的四个属性:
prefix:在标签开始添加上该字符串
suffixOverrides:在标签末尾去除上该字符串
suffix:在标签末尾添加上该字符串
prefixOverrides:在标签开始去除上该字符串
set标签
用在update语句中,如果字段参数不为null,则修改此参数
UserMapper
public interface UserMapper { public int updateUserById(User user); }
UserMapper.xml
<?xml version="1.0" encoding="UTF-8" ?> <!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd" > <!--用户mapper关系映射 --> <mapper namespace="cn.cnki.ref.mapper.UserMapper"> <update id="updateUserById"> update user <set> <if test="name != null">name=#{name},</if> <if test="age != null">age=#{age},</if> <if test="username != null">username=#{username},</if> <if test="email != null">email=#{email},</if> <if test="phone != null">phone=#{phone}</if> </set> <where> id=#{id} </where> </update> </mapper>
UserController
package cn.cnki.ref.controller; import cn.cnki.ref.mapper.UserMapper; import cn.cnki.ref.pojo.User; import org.springframework.beans.factory.annotation.Autowired; import org.springframework.web.bind.annotation.GetMapping; import org.springframework.web.bind.annotation.RestController; import java.util.List; @RestController public class UserController { @Autowired private UserMapper UserMapper; @GetMapping("/updateUserById") public int updateUserById() { User user = new User(1, null, null, 21, "12545564454", "14548445@qq.com"); return UserMapper.updateUserById(user); } }
测试结果
switch\\when标签
1描述需求:
满足id!=null查询id,
否则,看满足age否,
接着,看name是否满足,
最后,按age>10查询
2.改mapper映射
<select id="getUser" resultType="cn.cnki.ref.pojo.User"> select * from user where <choose> <when test="id != null">id=#{id} </when> <when test="age != null">age=#{age}</when> <when test="name != null">name=#{name} </when> <otherwise>age>10</otherwise> </choose> </select>
3.测试结果
foreach标签
1.需求描述:
查出多个id的user
2.添加mapper接口
public List<User> listById(List<Integer> ids);
3添加mapper映射
<select id="listById" resultType="cn.cnki.ref.pojo.User" parameterType="list"> select * from user where id in <foreach collection="list" item="id" separator="," open="(" close=")"> #{id} </foreach> </select>
4.测试
@GetMapping("/listById") public List<User> listById() { List<User> users = UserMapper.listById(Arrays.asList(1,2)); System.out.println(users); return users; }
5.foreach标签下的所有属性:
collection:获取的集合名,如果是list集合,springboot会把它的key值默认封装为list
item:遍历的单个属性值
separator:拼接隔离的字符串
open:在循环的开始拼接的字符串
close:在循环的结束拼接的字符串
index:索引,在map中作为key
bind
bind标签可以使用OGNL表达式创建一个变量并将其绑定到上下文中。
使用concat函数连接字符串,在mysql中,这个函数支持多个参数,但是在Oracle中只支持两个参数。 由于不同数据库之间的语法差异,如果更换了数据库,有些SQL语句可能就需要重写。 针对这种情况,可以使用bind标签来避免由于更换数据库带来的一些麻烦。
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