[CAY-2838] Vertical Inheritance: Problem setting db attribute to null via flattened path

• Type: Bug
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Affects Version/s: 4.2
• Fix Version/s: 4.2.1, 5.0-M1
• Component/s: Core Library
• Environment: Cayenne 4.2, Java 17, MacOS 14
• Assignee: Nikita Timofeev
• Reporter: Jadon Hansell
• Created: 23/Jan/24 22:59
• Updated: 05/Mar/24 11:30
• Resolved: 05/Mar/24 11:30

Description

While using vertical inheritance, I ran into a bug with a non-required attribute on a child DbEntity. The issue occurs when an attribute, accessed via a flattened path like 'child.attr' on the child's ObjEntity, is initially set to a value and then later changed to null. This causes Cayenne to attempt to set the primary key of the child db entity to null as well.

I've attached a patch that contains failing tests demonstrating this issue on both an ObjEntity's attribute and a belongs-to relationship.

A temporary workaround I've used is to relocate these columns to the parent DbEntity so the path isn't flattened.

 

The root of the problem appears to start in the ValuesCreationHandler. During the operation, it runs processFlattenedPath to identify the target row's ID, with add=false. This then iterates through the db path components and invokes processRelationship for each db relationship, again with add=false.

While processing the first path component, processRelationship creates an UPDATE row operation, attempting to update the child's uuid to its current value (case 2 in the comments). Normally, this would not cause an error. But, because the 'add' parameter is set to false, the ValuePropagationVisitor replaces the current ID with null.