fix: resolve constrained relations before insert

tests/test_importer_plugin_compat.py

@@ -1,3 +1,5 @@
+from typing import ClassVar
+
 from django.db import models
 
 from netbox_export.services.importer import _field_kwargs
@@ -16,6 +18,24 @@ class TenantManagedObject(models.Model):
         app_label = "compat_tests"
 
 
+class Platform(models.Model):
+    class Meta:
+        app_label = "compat_tests"
+
+
+class ConstrainedInstallation(models.Model):
+    platform = models.ForeignKey(Platform, on_delete=models.PROTECT, null=True)
+
+    class Meta:
+        app_label = "compat_tests"
+        constraints: ClassVar[list] = [
+            models.CheckConstraint(
+                condition=models.Q(platform__isnull=False),
+                name="compat_tests_installation_platform",
+            )
+        ]
+
+
 def tenant_record():
     return {
         "fields": {},
@@ -53,3 +73,23 @@ def test_unresolved_tenant_also_blocks_when_policy_detection_is_unavailable():
     assert unresolved == []
     assert unresolved_values == []
     assert missing_required == []
+
+
+def test_unresolved_relation_in_check_constraint_blocks_initial_save():
+    resolver = ReferenceResolver({}, [], lambda label: None)
+    record = {
+        "fields": {},
+        "relations": {"platform": {"ref": "compat_tests.platform:5"}},
+    }
+
+    kwargs, unresolved, unresolved_values, missing_required = _field_kwargs(
+        ConstrainedInstallation,
+        record,
+        resolver,
+        tenant_required=False,
+    )
+
+    assert kwargs is None
+    assert unresolved == []
+    assert unresolved_values == []
+    assert missing_required == []