feat: add uniqueness field validation for span questions

src/argilla_server/apis/v1/handlers/datasets/questions.py

@@ -48,7 +48,9 @@ async def create_dataset_question(
     question_create: QuestionCreate,
     current_user: User = Security(auth.get_current_user),
 ):
-    dataset = await _get_dataset_or_raise(db, dataset_id, with_fields=True)
+    # TODO: Review this flow since we're putting logic here that will be used internally by the context
+    #  Fields and questions are required to apply validations.
+    dataset = await _get_dataset_or_raise(db, dataset_id, with_fields=True, with_questions=True)
 
     await authorize(current_user, DatasetPolicyV1.create_question(dataset))
 

src/argilla_server/contexts/questions.py

@@ -120,6 +120,10 @@ def _validate_span_question_settings_before_create(
     if field not in field_names:
         raise ValueError(f"'{field}' is not a valid field name.\nValid field names are {field_names!r}")
 
+    for question in dataset.questions:
+        if question.type == QuestionType.span and field == question.parsed_settings.field:
+            raise ValueError(f"'{field}' is already used by span question with id '{question.id}'")
+
 
 async def create_question(db: AsyncSession, dataset: Dataset, question_create: QuestionCreate) -> Question:
     if dataset.is_ready:

tests/unit/api/v1/datasets/test_create_dataset_question.py

@@ -22,7 +22,7 @@
 from sqlalchemy import func, select
 from sqlalchemy.ext.asyncio import AsyncSession
 
-from tests.factories import DatasetFactory, TextFieldFactory
+from tests.factories import DatasetFactory, SpanQuestionFactory, TextFieldFactory
 
 
 @pytest.mark.asyncio
@@ -109,3 +109,32 @@ async def test_create_dataset_span_question_with_non_existent_field(
         }
 
         assert (await db.execute(select(func.count(Question.id)))).scalar() == 0
+
+    async def test_create_dataset_question_with_other_span_question_using_the_same_field(
+        self, async_client: AsyncClient, db: AsyncSession, owner_auth_header: dict
+    ):
+        dataset = await DatasetFactory.create()
+        question = await SpanQuestionFactory(dataset=dataset)
+
+        question_field = question.settings["field"]
+        await TextFieldFactory.create(name=question_field, dataset=dataset)
+
+        response = await async_client.post(
+            self.url(dataset.id),
+            headers=owner_auth_header,
+            json={
+                "name": "new-question",
+                "title": "Title",
+                "settings": {
+                    "type": QuestionType.span,
+                    "field": question_field,
+                    "options": [
+                        {"value": "label-c", "text": "Label C", "description": "Label C description"},
+                        {"value": "label-d", "text": "Label D", "description": "Label D description"},
+                    ],
+                },
+            },
+        )
+
+        assert response.status_code == 422
+        assert response.json() == {"detail": f"'field-a' is already used by span question with id '{question.id}'"}