Deleting foreign records
Deleting a record that is referenced in a foreign key field is not allowed by default. You can change this behavior in the blueprint.
The settings for what should happen on deleting a record can be found in the blueprint editor, in the field details of the connected class field. The standard setting is that the user should explicitly remove all connected objects. It is also possible to set cascading deletes, meaning that all connected objects are automatically removed. The other options are removing all references automatically, and allowing delete while keeping the references (not recommended).