Improve domain handler to catch duplicate domain error (baserow#4400)

* Add error handling when handler tries to create a duplicate domain

* Add changelog

* Simplify error handling.

* Rephrase changelog message

Author: paljort

backend/src/baserow/contrib/builder/domains/handler.py

@@ -17,6 +17,7 @@
 from baserow.core.db import specific_iterator
 from baserow.core.exceptions import IdDoesNotExist
 from baserow.core.models import Workspace
+from baserow.core.psycopg import is_unique_violation_error
 from baserow.core.registries import ImportExportConfig, application_type_registry
 from baserow.core.storage import get_default_storage
 from baserow.core.trash.handler import TrashHandler
@@ -131,7 +132,13 @@ def create_domain(
             prepared_values["domain_name"] = prepared_values["domain_name"].lower()
 
         domain = model_class(builder=builder, order=last_order, **prepared_values)
-        domain.save()
+
+        try:
+            domain.save()
+        except IntegrityError as error:
+            if is_unique_violation_error(error):
+                raise DomainNameNotUniqueError(prepared_values["domain_name"])
+            raise error
 
         return domain
 
@@ -171,7 +178,7 @@ def update_domain(self, domain: Domain, **kwargs) -> Domain:
         try:
             domain.save()
         except IntegrityError as error:
-            if "unique" in str(error) and "domain_name" in prepared_values:
+            if is_unique_violation_error(error):
                 raise DomainNameNotUniqueError(prepared_values["domain_name"])
             raise error
 

backend/tests/baserow/contrib/builder/domains/test_domain_handler.py

@@ -3,6 +3,7 @@
 from baserow.contrib.builder.domains.domain_types import CustomDomainType
 from baserow.contrib.builder.domains.exceptions import (
     DomainDoesNotExist,
+    DomainNameNotUniqueError,
     DomainNotInBuilder,
 )
 from baserow.contrib.builder.domains.handler import DomainHandler
@@ -68,6 +69,21 @@ def test_create_domain(data_fixture):
     assert domain.domain_name == "test.com"
 
 
+@pytest.mark.django_db
+def test_create_domain_with_duplicate_name(data_fixture):
+    builder = data_fixture.create_builder_application()
+    domain_name = "test.com"
+
+    DomainHandler().create_domain(CustomDomainType(), builder, domain_name=domain_name)
+
+    with pytest.raises(DomainNameNotUniqueError) as exc_info:
+        DomainHandler().create_domain(
+            CustomDomainType(), builder, domain_name=domain_name
+        )
+
+    assert exc_info.value.domain_name == domain_name
+
+
 @pytest.mark.django_db
 def test_delete_domain(data_fixture):
     domain = data_fixture.create_builder_custom_domain()
@@ -88,6 +104,24 @@ def test_update_domain(data_fixture):
     assert domain.domain_name == "new.com"
 
 
+@pytest.mark.django_db
+def test_update_domain_with_duplicate_name(data_fixture):
+    builder = data_fixture.create_builder_application()
+    domain = data_fixture.create_builder_custom_domain(
+        domain_name="test.com", builder=builder
+    )
+
+    existing_domain = "other.com"
+    DomainHandler().create_domain(
+        CustomDomainType(), builder, domain_name=existing_domain
+    )
+
+    with pytest.raises(DomainNameNotUniqueError) as exc_info:
+        DomainHandler().update_domain(domain, domain_name=existing_domain)
+
+    assert exc_info.value.domain_name == existing_domain
+
+
 @pytest.mark.django_db
 def test_order_domains(data_fixture):
     builder = data_fixture.create_builder_application()

changelog/entries/unreleased/bug/4399_added_error_handling_when_the_domain_handler_tries_to_create.json

@@ -0,0 +1,9 @@
+{
+    "type": "bug",
+    "message": "Fixed a bug where domain names were not correctly validated during domain creation.",
+    "issue_origin": "github",
+    "issue_number": 4399,
+    "domain": "builder",
+    "bullet_points": [],
+    "created_at": "2025-12-05"
+}