mybatisplus getById
时间: 2023-09-29 22:10:53 浏览: 122
在Mybatis-plus中,getById方法用于根据主键id查询记录。它是CRUD接口中的一个方法,用于查询单个记录。getById方法会根据传入的id值,通过Mybatis-plus的映射机制,自动执行对应的SQL语句,并返回查询结果。在使用getById方法时,需要注意以下几点:
1. 需要传入正确的id值,否则可能查询不到对应的记录。
2. 如果查询的是同一条记录多次,需要注意获取值的内存地址。如果修改了对象中的非数据库内容,可能会影响后续查询的结果。
相关问题
mybatisplus使用getById
MyBatis Plus is a powerful library that enhances the functionality of MyBatis, a Java-based persistence framework. To retrieve a record by its primary key using MyBatis Plus, you can use the `getById` method provided by the `BaseMapper` interface.
Here's an example of how to use the `getById` method:
```java
import com.baomidou.mybatisplus.core.mapper.BaseMapper;
import org.springframework.beans.factory.annotation.Autowired;
public class YourMapperClass {
@Autowired
private BaseMapper<YourEntityClass> baseMapper;
public YourEntityClass getEntityById(Long id) {
return baseMapper.getById(id);
}
}
```
In the above example, `YourMapperClass` is the class where you define your mapper methods. `YourEntityClass` represents the entity class for which you want to retrieve a record. You can autowire the `BaseMapper` interface using the `@Autowired` annotation.
Then, you can use the `getById` method of `BaseMapper` by passing the primary key value to retrieve the corresponding record. The method will return an instance of `YourEntityClass` if found, or `null` if no matching record is found.
Remember to replace `YourMapperClass` and `YourEntityClass` with your own mapper and entity classes accordingly.
怎么使用mybatisplus
MybatisPlus 是 Mybatis 的增强工具,在 Mybatis 的基础上,简化了开发流程,提高了开发效率。使用 MybatisPlus 可以省去很多重复的 CRUD 操作代码,同时还提供了很多实用的功能,如分页、逻辑删除、乐观锁等。
使用 MybatisPlus 需要进行以下步骤:
1. 引入 MybatisPlus 的依赖:
```xml
<dependency>
<groupId>com.baomidou</groupId>
<artifactId>mybatis-plus-boot-starter</artifactId>
<version>3.x.x</version>
</dependency>
```
2. 配置 MybatisPlus:
在 Spring Boot 中,可以在 application.yml 或 application.properties 文件中添加以下配置:
```yaml
mybatis-plus:
mapper-locations: classpath*:mapper/**/*.xml # mapper.xml 文件的位置
type-aliases-package: com.example.entity # 实体类所在的包名
```
3. 编写实体类:
```java
@Data
public class User {
private Long id;
private String name;
private Integer age;
private String email;
}
```
4. 编写 Mapper 接口:
```java
public interface UserMapper extends BaseMapper<User> {
}
```
5. 使用 MybatisPlus 进行 CRUD 操作:
```java
@Service
public class UserServiceImpl implements UserService {
@Autowired
private UserMapper userMapper;
@Override
public User getById(Long id) {
return userMapper.selectById(id);
}
@Override
public List<User> list() {
return userMapper.selectList(null);
}
@Override
public int save(User user) {
return userMapper.insert(user);
}
@Override
public int update(User user) {
return userMapper.updateById(user);
}
@Override
public int delete(Long id) {
return userMapper.deleteById(id);
}
}
```
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