java中mybatisplus实现IS NULL

以下是Java中使用MybatisPlus实现IS NULL的方法：

1.使用QueryWrapper的isNull方法：

QueryWrapper<User> wrapper = new QueryWrapper<>();
wrapper.isNull("column_name");
List<User> userList = userMapper.selectList(wrapper);

2.使用LambdaQueryWrapper的isNull方法：

LambdaQueryWrapper<User> lambdaWrapper = new LambdaQueryWrapper<>();
lambdaWrapper.isNull(User::getColumnName);
List<User> userList = userMapper.selectList(lambdaWrapper);

其中，column_name是需要查询的列名，User是实体类名，getColumnName是获取该列值的方法名。

相关问题

mybatisplus querywrapper isnull

MyBatis-Plus QueryWrapper provides a convenient way to construct SQL queries in MyBatis, including conditions like "IS NULL". To use the "IS NULL" condition in QueryWrapper, you can use the method `isNull` on the desired column. Here's an example:

import com.baomidou.mybatisplus.core.conditions.query.QueryWrapper;

QueryWrapper<Entity> queryWrapper = new QueryWrapper<>();
queryWrapper.isNull("column_name");

In the above example, replace `"column_name"` with the actual name of the column in your entity where you want to check for null values. This will generate a SQL condition for checking if the specified column is null.

You can also combine multiple conditions using other methods provided by QueryWrapper, such as `eq`, `ne`, `gt`, `ge`, `lt`, `le`, etc.

mybatisplus查询json字段为null

你可以使用MyBatis Plus提供的`LambdaQueryWrapper`类来查询JSON字段为null的记录。具体操作如下：

1. 导入相关依赖：

<dependency>
    <groupId>com.baomidou</groupId>
    <artifactId>mybatis-plus-extension</artifactId>
    <version>3.4.2</version>
</dependency>

2. 定义实体类，包含JSON字段：

@Data
public class User {
    private Long id;
    private String name;
    private String email;
    private JSONObject extra;
}

3. 使用`LambdaQueryWrapper`查询：

LambdaQueryWrapper<User> queryWrapper = new LambdaQueryWrapper<>();
queryWrapper.isNull(User::getExtra);
List<User> userList = userMapper.selectList(queryWrapper);

以上代码会查询`extra`字段为null的记录，并返回一个`List<User>`类型的结果。注意，`extra`字段必须是JSON类型的才能使用`JSONObject`类型进行操作。