mybatis-plus select
时间: 2023-04-25 18:01:22 浏览: 69
Mybatis-Plus 是一个 Mybatis 的增强工具,它提供了很多实用的功能,其中包括 select 查询。通过 Mybatis-Plus 的 select 查询,可以方便地进行单表查询、多表联合查询、分页查询等操作,大大提高了开发效率。同时,Mybatis-Plus 还支持 Lambda 表达式查询,使得查询更加简洁易懂。
相关问题
mybatis-plus selectOne
MyBatis-Plus is a popular Java persistence framework that extends the functionality of MyBatis. It provides additional features and simplifies the development of MyBatis-based applications.
In MyBatis-Plus, the `selectOne` method is used to query a single record from the database based on the specified conditions. It returns a single entity object that matches the query criteria.
Here is an example of using `selectOne` in MyBatis-Plus:
```java
User user = new User();
user.setId(1);
User result = userMapper.selectOne(new QueryWrapper<>(user));
```
In this example, we create a `User` object and set the `id` property to 1. We then use `selectOne` method of the `userMapper` to query a single record from the database based on the `id` match.
Please note that `userMapper` is an instance of the MyBatis mapper interface, which is automatically generated by MyBatis-Plus based on your entity class. The `QueryWrapper` is used to specify the query conditions.
Hope this helps! Let me know if you have any more questions.
mybatis-plus selectPage
MyBatis-Plus is an enhanced version of MyBatis, a popular open-source Java persistence framework. It provides additional features and utilities to simplify database operations.
To perform a pagination query using MyBatis-Plus, you can use the `selectPage` method provided by the `com.baomidou.mybatisplus.core.mapper.BaseMapper` interface.
Here's an example of how to use the `selectPage` method:
```java
import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;
import com.baomidou.mybatisplus.extension.plugins.pagination.Page;
import com.baomidou.mybatisplus.core.metadata.IPage;
// Assuming you have a mapper interface that extends BaseMapper
public interface YourMapper extends BaseMapper<YourEntity> {
}
// In your service or repository class
@Autowired
private YourMapper yourMapper;
public IPage<YourEntity> getEntityPage(int pageNo, int pageSize) {
// Create a Page object with the desired page number and page size
Page<YourEntity> page = new Page<>(pageNo, pageSize);
// Create a QueryWrapper object for your query conditions (if any)
QueryWrapper<YourEntity> queryWrapper = new QueryWrapper<>();
// Perform the pagination query using selectPage
return yourMapper.selectPage(page, queryWrapper);
}
```
In the above example, `YourEntity` represents your entity class, `YourMapper` is the mapper interface extending `BaseMapper`, and `yourMapper` is an instance of the mapper interface injected using the `@Autowired` annotation.
The `getEntityPage` method takes two arguments: `pageNo` for the desired page number and `pageSize` for the number of records per page. It creates a `Page` object with these parameters and a `QueryWrapper` object for any query conditions. Finally, it calls the `selectPage` method on the mapper interface to perform the pagination query and returns the resulting `IPage` object.
You can customize the `QueryWrapper` object to add various query conditions such as equals, greater than, less than, etc., depending on your requirements.
Please note that this is just a basic example, and there are many other features and options available in MyBatis-Plus for pagination and database operations. You can refer to the official documentation for more details: [MyBatis-Plus Documentation](https://mybatis.plus/)