## 一、Spring Boot整合Mybatis Plus
通过maven坐标引入依赖
~~~
<!-- mybatis -->
<dependency>
<groupId>com.baomidou</groupId>
<artifactId>mybatis-plus-boot-starter</artifactId>
<version>3.1.2</version>
</dependency>
<!-- mysql -->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<scope>runtime</scope>
</dependency>
<!-- lombok -->
<dependency>
<groupId>org.projectlombok</groupId>
<artifactId>lombok</artifactId>
<optional>true</optional>
</dependency>
~~~
application配置数据源及日志输出级别
~~~
# 配置数据源
spring:
datasource:
driver-class-name: com.mysql.cj.jdbc.Driver
url: jdbc:mysql://192.168.161.3:3306/testdb?useUnicode=true&characterEncoding=utf-8&useSSL=false
username: test
password: <填上数据库访问密码>
# 配置日志
logging:
level:
root: warn
com.zimug.boot.launch.mapper: trace
~~~
第三步：配置Mybatis的Mapper类文件的包扫描路径
~~~
@SpringBootApplication
@MapperScan(basePackages = {"com.zimug.boot.launch.mapper"})
public class BootLaunchApplication {
public static void main(String[] args) {
SpringApplication.run(BootLaunchApplication.class, args);
}
}
~~~
## 二、编码构建实体和Mapper
编写实体类`User.java`，对应的数据库表创建SQL在文末。
~~~
@Data //lombok注解
public class User {
private Long id;
private String name;
private Integer age;
private String email;
}
~~~
编写Mapper类`UserMapper.java`
~~~
public interface UserMapper extends BaseMapper<User> {
}
~~~
## 三、CRUD基础使用案例
### 3.1.增加一条记录
~~~
User user = new User();
user.setName("字母哥");
user.setAge(18);
int row = userMapper.insert(user);
System.out.println("影响记录数："+row);
System.out.println("雪花算法id: "+user.getId());
~~~
写了上面的java代码，MP将会自动的根据java代码构造下面的SQL去数据库执行。注意：主键默认采用雪花算法
~~~
# 主键自动填充了雪花算法
INSERT INTO user ( id, name, age)
VALUES ( ?, ?, ? )
~~~
### 3.2.根据主键删除一条记录
~~~
int rows = userMapper.deleteById(1170243901535006722L);
System.out.println("影响记录数：" + rows);
~~~
1170243901535006722L是数据插入的时候根据雪花算法生成的id
~~~
DELETE FROM user
WHERE id=?
~~~
### 3.3.根据条件删除记录
~~~
//构造条件
Map<String,Object> map = new HashMap<>();
map.put("name","字母哥");
map.put("age",18);
//执行删除
int rows = userMapper.deleteByMap(map);
System.out.println("影响记录数：" + rows);
~~~
~~~
DELETE FROM user
WHERE name = ?
AND age = ?
~~~
### 3.4.根据主键查询一条数据
~~~
User user = userMapper.selectById(1089911557332887553L);
System.out.println(user);
~~~
~~~
SELECT id,name,age,email
FROM user
WHERE id=?
~~~
### 3.5.根据ids批量查找数据
~~~
List<Long> ids = Arrays.asList(
1087982257332887553L,
1094590409767661570L,
1094592041087729666L
);
List<User> list = userMapper.selectBatchIds(ids);
list.forEach(System.out::println);
~~~
~~~
SELECT id,name,age,email
FROM user
WHERE id IN ( ? , ? , ? )
~~~
### 3.6.根据指定参数查询
~~~
Map<String, Object> map = new HashMap<>();
//map的key指代的是mysql表中的列名，并非java实体的属性名
map.put("name", "Jone");
List<User> list = userMapper.selectByMap(map);
list.forEach(System.out::println);
~~~
~~~
SELECT id,name,age,email
FROM user
WHERE name = ?
~~~
### 3.7.指定查询结果字段
1.
~~~
QueryWrapper<User> query = new QueryWrapper<>();
query.select("name", "age") //指定查询结果字段
.in("age", Arrays.asList(30, 31, 34, 35))
.last("limit 1");
List<User> list = userMapper.selectList(query);
list.forEach(System.out::println);
~~~
~~~
SELECT name,age
FROM user
WHERE age IN (?,?,?,?)
LIMIT 1
~~~
2.
~~~
QueryWrapper<User> query = new QueryWrapper<>();
query.like("name", "J") //like是MP的条件构造器，表示"模糊查询"
.lt("age", 40) //lt是MP的条件构造器，表示"小于"关系
.select("name", "age");
List<Map<String, Object>> maps = userMapper.selectMaps(query);
maps.forEach(System.out::println);
~~~
~~~
SELECT name,age
FROM user
WHERE name LIKE ?
AND age < ?
~~~
### 3.8.通过主键id修改数据
~~~
User user = new User();
user.setId(1088248199570832385L);
user.setAge(18);
user.setEmail("hadoopcn2@163.com");
int rows = userMapper.updateById(user);
System.out.println("影响记录数：" + rows);
~~~
~~~
UPDATE user
SET age=?, email=?
WHERE id=?
~~~
### 3.9.根据UpdateWrapper自定义条件修改数据
~~~
UpdateWrapper<User> update = new UpdateWrapper<>();
update.eq("name", "Jack").eq("age", 28); //eq是MP的条件构造器，表示"等于"关系
User user = new User();
user.setAge(29);
user.setEmail("hadoopcn2@163.com");
int rows = userMapper.update(user, update);
System.out.println("影响记录数：" + rows);
~~~
~~~
UPDATE user
SET age=?, email=?
WHERE name = ?
AND age = ?
~~~
## 附录---测试SQL：
~~~
DROP TABLE IF EXISTS user;
CREATE TABLE user
(
id BIGINT(20) NOT NULL COMMENT '主键ID',
name VARCHAR(30) NULL DEFAULT NULL COMMENT '姓名',
age INT(11) NULL DEFAULT NULL COMMENT '年龄',
email VARCHAR(50) NULL DEFAULT NULL COMMENT '邮箱',
PRIMARY KEY (id)
);
~~~
其对应的数据库 Data 脚本如下：
~~~
DELETE FROM user;
INSERT INTO user (id, name, age, email) VALUES
(1, 'Jone', 18, 'test1@baomidou.com'),
(2, 'Jack', 20, 'test2@baomidou.com'),
(3, 'Tom', 28, 'test3@baomidou.com'),
(4, 'Sandy', 21, 'test4@baomidou.com'),
(5, 'Billie', 24, 'test5@baomidou.com');
~~~
