contribute to constraints test - minimal

tests/contribute_to_meta/fields.py

@@ -0,0 +1,14 @@
+from django.db import models
+
+
+class ConstraintField(models.CharField):
+    """A field that contributes a DB contraint to the model's Meta"""
+
+    def contribute_to_class(self, cls, name, private_only=False):
+        super().contribute_to_class(cls, name, private_only)
+        cls._meta.constraints.append(
+            models.CheckConstraint(
+                check=models.Q(**{name: "valid"}),
+                name=f"test_constraint_{cls.__name__.lower()}",
+            )
+        )

tests/contribute_to_meta/migrations/.gitignore

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+0001_initial.py

tests/contribute_to_meta/models.py

@@ -0,0 +1,14 @@
+from django.db import models
+
+from .fields import ConstraintField
+
+
+class ModelA(models.Model):
+    field = ConstraintField(max_length=10)
+
+
+class ModelC(models.Model):
+    class Meta:
+        constraints = []
+
+    field = ConstraintField(max_length=10)

tests/contribute_to_meta/tests.py

@@ -0,0 +1,49 @@
+from pathlib import Path
+
+from django.core.management import call_command
+from django.db import IntegrityError
+from django.test import TestCase, skipUnlessDBFeature
+
+from .models import ModelA, ModelC
+
+
+@skipUnlessDBFeature("supports_table_check_constraints")
+class ConstraintsTests(TestCase):
+    """Check that the constraints allow valid values and reject invalid ones"""
+
+    def test_ModelA_constraint(self):
+        ModelA.objects.create(field="valid")
+        with self.assertRaises(IntegrityError):
+            ModelA.objects.create(field="invalid")
+
+    def test_ModelC_constraint(self):
+        ModelC.objects.create(field="valid")
+        with self.assertRaises(IntegrityError):
+            ModelC.objects.create(field="invalid")
+
+
+class ConstraintsMigrationsTests(TestCase):
+    """Check that migrations correctly generate the constraints"""
+
+    @classmethod
+    def setUpClass(cls):
+        super().setUpClass()
+        # Clean and recreate migration files for further inspection
+        init_file = Path(__file__).parent / "migrations" / "0001_initial.py"
+        init_file.unlink(missing_ok=True)
+        call_command("makemigrations", verbosity=0)
+        cls.migration_content = init_file.read_text()
+
+    def test_ModelA(self):
+        # check migration contents
+        self.assertTrue(
+            "test_constraint_modela" in self.migration_content,
+            "Could not find constraint `test_constraint_modela` in migration",
+        )
+
+    def test_ModelC(self):
+        # check migration contents
+        self.assertTrue(
+            "test_constraint_modelc" in self.migration_content,
+            "Could not find constraint `test_constraint_modelc` in migration",
+        )