QSqlQueryisValid

QSqlQuery isValid is a method of the QSqlQuery class in the Qt framework. It is used to check if a QSqlQuery object represents a valid and active query. A QSqlQuery object can become invalid for several reasons, such as an error during query execution, the query returning no results, or the query being prematurely closed.

The isValid() method returns true if the query is valid and false otherwise. A valid query means that it has been successfully prepared or executed, and it is ready to be used for fetching data or performing other operations. If isValid() returns false, attempting to perform operations like fetching records or executing the query again might lead to undefined behavior or errors.

It is good practice to check the result of isValid() after executing a query or after performing operations that might affect the query's state. This helps in robust error handling and ensures that your application behaves predictably. For instance, after calling exec() on a QSqlQuery, you would typically check isValid() before proceeding to iterate through the results using next(). If the query fails to execute, isValid() will return false, and you can then handle the error gracefully, perhaps by logging the error message obtained from lastError().