feat #3037 Rewrite exclusive fields check as constraint

src/core/model_utils.py

@@ -741,21 +741,24 @@ def NotImplementedField(self):
     raise NotImplementedError
 
 
-def validate_exclusive_fields(obj, fields):
+def check_exclusive_fields_constraint(fields):
     """
     Checks that only one of several exclusive fields is populated.
     For example, CreditRecord has author, frozen_author, and preprint_author,
     but only one should be populated.
-    Call this function during the model's save method before the call to super.
+    Set this as one of the constraints in a model's Meta.constraints
     :param fields: iterable of field names that should be exclusive
     """
-    populated_fields = set()
-    for field in fields:
-        if getattr(obj, field):
-            populated_fields.add(field)
-    if len(populated_fields) > 1:
-        data = {field: getattr(obj, field) for field in populated_fields}
-        raise ValidationError(
-            f'{obj} of type {obj._meta.model} was saved with ' \
-            f'more than one exclusive fields: {data}'
-        )
+    main_query = models.Q()
+    for this_field in fields:
+        query_piece = models.Q()
+        query_piece &= Q((f'{this_field}__isnull', False))
+        other_fields = [field for field in fields if field != this_field]
+        for other_field in other_fields:
+            query_piece &= Q((f'{other_field}__isnull', True))
+        main_query |= Q(query_piece)
+    constraint = models.CheckConstraint(
+        check=main_query,
+        name='exclusive_fields_constraint'
+    )
+    return constraint

src/submission/models.py

@@ -2258,6 +2258,11 @@ class CreditRecord(AbstractLastModifiedModel):
     class Meta:
         verbose_name = 'CRediT record'
         verbose_name_plural = 'CRediT records'
+        constraints = [
+            model_utils.check_exclusive_fields_constraint(
+                ['author', 'frozen_author', 'preprint_author']
+            )
+        ]
 
     author = models.ForeignKey(
         'core.Account',
@@ -2293,11 +2298,6 @@ def uri(self):
     def all_roles(self):
         return CREDIT_ROLE_CHOICES
 
-    def save(self, *args, **kwargs):
-        exclusive_fields = ['author', 'frozen_author', 'preprint_author']
-        model_utils.validate_exclusive_fields(self, fields=exclusive_fields)
-        super().save(*args, **kwargs)
-
 
 class Section(AbstractLastModifiedModel):
     journal = models.ForeignKey(

src/submission/tests.py

@@ -7,6 +7,7 @@
 from mock import Mock
 import os
 
+from django.db import IntegrityError
 from django.core.management import call_command
 from django.http import Http404
 from django.test import TestCase, TransactionTestCase
@@ -979,8 +980,8 @@ def setUpTestData(cls):
             article=cls.article_one,
         )
 
-    def test_save_checks_exclusive_fields(self):
-        with self.assertRaises(ValidationError):
+    def test_credit_record_has_exclusive_fields_constraint(self):
+        with self.assertRaises(IntegrityError):
             models.CreditRecord.objects.create(
                 author=self.author_one,
                 frozen_author=self.frozen_author_one,