Modifying database query if field is missing

[DDSGooch]

Hi, I've been working with Hot Chocolate for a while buy have just started trying out some more advanced ideas.

If a field isn't specified in the graphql query, I'd like to modify the database query to filter on another field.

I've read up all the details about Extending Filtering but can't find any simple examples of something similar.

Hope you can help. Many thanks