## 一、Spring Boot整合Mybatis Plus
通過maven坐標引入依賴
~~~
<!-- 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配置數據源及日志輸出級別
~~~
# 配置數據源
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: <填上數據庫訪問密碼>
# 配置日志
logging:
level:
root: warn
com.zimug.boot.launch.mapper: trace
~~~
第三步：配置Mybatis的Mapper類文件的包掃描路徑
~~~
@SpringBootApplication
@MapperScan(basePackages = {"com.zimug.boot.launch.mapper"})
public class BootLaunchApplication {
public static void main(String[] args) {
SpringApplication.run(BootLaunchApplication.class, args);
}
}
~~~
## 二、編碼構建實體和Mapper
編寫實體類`User.java`，對應的數據庫表創建SQL在文末。
~~~
@Data //lombok注解
public class User {
private Long id;
private String name;
private Integer age;
private String email;
}
~~~
編寫Mapper類`UserMapper.java`
~~~
public interface UserMapper extends BaseMapper<User> {
}
~~~
## 三、CRUD基礎使用案例
### 3.1.增加一條記錄
~~~
User user = new User();
user.setName("字母哥");
user.setAge(18);
int row = userMapper.insert(user);
System.out.println("影響記錄數："+row);
System.out.println("雪花算法id: "+user.getId());
~~~
寫了上面的java代碼，MP將會自動的根據java代碼構造下面的SQL去數據庫執行。注意：主鍵默認采用雪花算法
~~~
# 主鍵自動填充了雪花算法
INSERT INTO user ( id, name, age)
VALUES ( ?, ?, ? )
~~~
### 3.2.根據主鍵刪除一條記錄
~~~
int rows = userMapper.deleteById(1170243901535006722L);
System.out.println("影響記錄數：" + rows);
~~~
1170243901535006722L是數據插入的時候根據雪花算法生成的id
~~~
DELETE FROM user
WHERE id=?
~~~
### 3.3.根據條件刪除記錄
~~~
//構造條件
Map<String,Object> map = new HashMap<>();
map.put("name","字母哥");
map.put("age",18);
//執行刪除
int rows = userMapper.deleteByMap(map);
System.out.println("影響記錄數：" + rows);
~~~
~~~
DELETE FROM user
WHERE name = ?
AND age = ?
~~~
### 3.4.根據主鍵查詢一條數據
~~~
User user = userMapper.selectById(1089911557332887553L);
System.out.println(user);
~~~
~~~
SELECT id,name,age,email
FROM user
WHERE id=?
~~~
### 3.5.根據ids批量查找數據
~~~
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.根據指定參數查詢
~~~
Map<String, Object> map = new HashMap<>();
//map的key指代的是mysql表中的列名，并非java實體的屬性名
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.指定查詢結果字段
1.
~~~
QueryWrapper<User> query = new QueryWrapper<>();
query.select("name", "age") //指定查詢結果字段
.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的條件構造器，表示"模糊查詢"
.lt("age", 40) //lt是MP的條件構造器，表示"小于"關系
.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.通過主鍵id修改數據
~~~
User user = new User();
user.setId(1088248199570832385L);
user.setAge(18);
user.setEmail("hadoopcn2@163.com");
int rows = userMapper.updateById(user);
System.out.println("影響記錄數：" + rows);
~~~
~~~
UPDATE user
SET age=?, email=?
WHERE id=?
~~~
### 3.9.根據UpdateWrapper自定義條件修改數據
~~~
UpdateWrapper<User> update = new UpdateWrapper<>();
update.eq("name", "Jack").eq("age", 28); //eq是MP的條件構造器，表示"等于"關系
User user = new User();
user.setAge(29);
user.setEmail("hadoopcn2@163.com");
int rows = userMapper.update(user, update);
System.out.println("影響記錄數：" + rows);
~~~
~~~
UPDATE user
SET age=?, email=?
WHERE name = ?
AND age = ?
~~~
## 附錄---測試SQL：
~~~
DROP TABLE IF EXISTS user;
CREATE TABLE user
(
id BIGINT(20) NOT NULL COMMENT '主鍵ID',
name VARCHAR(30) NULL DEFAULT NULL COMMENT '姓名',
age INT(11) NULL DEFAULT NULL COMMENT '年齡',
email VARCHAR(50) NULL DEFAULT NULL COMMENT '郵箱',
PRIMARY KEY (id)
);
~~~
其對應的數據庫 Data 腳本如下：
~~~
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');
~~~
