Jadon Hansell created CAY-2838:
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Summary: Vertical Inheritance: Problem setting db attribute to
null via flattened path
Key: CAY-2838
URL: https://issues.apache.org/jira/browse/CAY-2838
Project: Cayenne
Issue Type: Bug
Affects Versions: 4.2
Environment: Cayenne 4.2, Java 17, MacOS 14
Reporter: Jadon Hansell
Attachments: NullifyFlattenedTests.patch
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.
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