how to check duplicate record in entity framework core

If the database query is expensive or time-consuming, executing it twice (once with all parameters and once with a subset of parameters) can have a performance impact. This might not be noticeable for small datasets or simple queries, but it could become an issue for larger datasets or complex queries.

The code becomes more complex with additional conditional checks and duplicated queries. This can make the code harder to understand, debug, and maintain. Also depending on the database schema and the meaning of the parameters, passing null for a parameter might result in different data being retrieved.

To handle a situation where one of the parameters can be null when retrieving dbValue, you can modify your code to conditionally include the nullable parameter in the query. Here's an example:

var dbValue = _dbContext.GetEstrazioneVenditeByIdAziIdDocIdRig(
    destinationRecord.IdAzienda,
    destinationRecord.IdDocumento,
    destinationRecord.IdRiga,
    destinationRecord.IdMovpartite
);

// If destinationRecord.IdMovpartite is null, try the query without including the parameter
if (dbValue == null && destinationRecord.IdMovpartite == null)
{
    dbValue = _dbContext.GetEstrazioneVenditeByIdAziIdDocIdRig(
        destinationRecord.IdAzienda,
        destinationRecord.IdDocumento,
        destinationRecord.IdRiga,
        null // Pass null explicitly for the nullable parameter
    );
}

// Handle the result (dbValue) accordingly

In the code above, we first try to retrieve dbValue using all four parameters. If it returns null and the destinationRecord.IdMovpartite is also null, we retry the query by explicitly passing null for the nullable parameter.

This way, you can retrieve dbValue with the four keys, even if one of the parameters (destinationRecord.IdMovpartite) can be null. Adjust the logic as per your specific requirements and handle the result accordingly in your code.

It seems that somewhere in your code you are assigning null to a non-nullable value.

For example if you have a variable that is declared as long "long a;" it won't be able to hold null.

you need to declare your property with "?" for example "long? a;"