Java SSM框架之MyBatis3(八)MyBatis之动态SQL
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,'','4567899@qq.com'),(2,'李四','ls',19,'','567657642@qq.com'),(3,'王五','ww',20,'','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 */;
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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