[CAY-2792] Fix Insertion Order For Reflexive DataObjects

• Type: Bug
• Status: Closed
• Priority: Critical
• Resolution: Fixed
• Affects Version/s: 4.2.RC2, 4.2.RC1
• Fix Version/s: 4.2, 5.0-M1
• Component/s: Core Library
• Environment: Java 17
• Assignee: Nikita Timofeev
• Reporter: Matt Watson
• Created: 06/Feb/23 18:08
• Updated: 10/Feb/23 06:41
• Resolved: 10/Feb/23 06:41

Description

For terminology's sake, I assume Reflexive refers to when you have 2 objects of the same Model, that are related, in this case, parent/child (ToOne/HasMany). If this assumption is incorrect we can rename the title.

For a little history on this, we never encountered this bug until we upgraded to 4.2.RC1, and I recently tested on 4.2.RC2 and the bug still exists.

For a while I thought this was only a bug in our environment, thinking that our code was causing the issue because Cayenne has a passing test in CayenneDataObjectRelationshipsIT.testReflexiveRelationshipInsertOrder1. But as I got to digging, the error occurs when the parent also has a relationship to some "Other" object that is not of the same model.

The pull request has a breaking test. I have not worked on a fix yet, but will begin investigating. I suspect it has to do with the work done in CAY-2571, but I am not certain yet.

The issue is that Cayenne randomly tries to commit the child record in front of the parent record, therefore the database throws a Foreign Key error, since the parent does not yet exist when the child is inserted. Because of this randomness, my breaking test attempts this process 100 times. You will also see another test that passes with the same Models but without setting the "ToOne" Other object.

here is a look at the code that "randomly" fails:

    public void addReflexiveParentAndChildWithOtherRelationshipOnParent() {
        // can add Reflexive Parent (that belongsTo Other) and Child,
        // we will do this 100 times, because it randomly does it correctly/incorrectly

        // given some "other" Object
        final Other other = context.newObject(Other.class);
        other.setName("OtherB");
        context.commitChanges();

        final int attempts = 100;
        int errors = 0;

        for (int i = 0; i < attempts; i++) {
            // when parent is created and associated to "Other"

            final Reflexive parent = context.newObject(Reflexive.class);
            parent.setName("parentB"+i);
            parent.setToOther(other);

            // and child is created and associated to "Parent"
            final Reflexive child = context.newObject(Reflexive.class);
            child.setName("childB"+i);
            child.setToParent(parent);

            try {
                context.commitChanges();
            } catch (final Exception e) {
                errors++;
                e.printStackTrace();
                context.rollbackChanges();
            }
        }

        // then no error occurred
        assertEquals(String.format("Failed on %s of %s attempts.", errors, attempts), 0, errors);
    }