diff --git a/api/services/dataset_service.py b/api/services/dataset_service.py
index 7841b8b33d..8097a6daa0 100644
--- a/api/services/dataset_service.py
+++ b/api/services/dataset_service.py
@@ -1636,6 +1636,20 @@ class DocumentService:
                         return [], ""
                     db.session.add(dataset_process_rule)
                     db.session.flush()
+                else:
+                    # Fallback when no process_rule provided in knowledge_config:
+                    # 1) reuse dataset.latest_process_rule if present
+                    # 2) otherwise create an automatic rule
+                    dataset_process_rule = getattr(dataset, "latest_process_rule", None)
+                    if not dataset_process_rule:
+                        dataset_process_rule = DatasetProcessRule(
+                            dataset_id=dataset.id,
+                            mode="automatic",
+                            rules=json.dumps(DatasetProcessRule.AUTOMATIC_RULES),
+                            created_by=account.id,
+                        )
+                        db.session.add(dataset_process_rule)
+                        db.session.flush()
             lock_name = f"add_document_lock_dataset_id_{dataset.id}"
             try:
                 with redis_client.lock(lock_name, timeout=600):
@@ -1647,65 +1661,67 @@ class DocumentService:
                         if not knowledge_config.data_source.info_list.file_info_list:
                             raise ValueError("File source info is required")
                         upload_file_list = knowledge_config.data_source.info_list.file_info_list.file_ids
-                        for file_id in upload_file_list:
-                            file = (
-                                db.session.query(UploadFile)
-                                .where(UploadFile.tenant_id == dataset.tenant_id, UploadFile.id == file_id)
-                                .first()
+                        files = (
+                            db.session.query(UploadFile)
+                            .where(
+                                UploadFile.tenant_id == dataset.tenant_id,
+                                UploadFile.id.in_(upload_file_list),
                             )
+                            .all()
+                        )
+                        if len(files) != len(set(upload_file_list)):
+                            raise FileNotExistsError("One or more files not found.")
 
-                            # raise error if file not found
-                            if not file:
-                                raise FileNotExistsError()
-
-                            file_name = file.name
+                        file_names = [file.name for file in files]
+                        db_documents = (
+                            db.session.query(Document)
+                            .where(
+                                Document.dataset_id == dataset.id,
+                                Document.tenant_id == current_user.current_tenant_id,
+                                Document.data_source_type == "upload_file",
+                                Document.enabled == True,
+                                Document.name.in_(file_names),
+                            )
+                            .all()
+                        )
+                        documents_map = {document.name: document for document in db_documents}
+                        for file in files:
                             data_source_info: dict[str, str | bool] = {
-                                "upload_file_id": file_id,
+                                "upload_file_id": file.id,
                             }
-                            # check duplicate
-                            if knowledge_config.duplicate:
-                                document = (
-                                    db.session.query(Document)
-                                    .filter_by(
-                                        dataset_id=dataset.id,
-                                        tenant_id=current_user.current_tenant_id,
-                                        data_source_type="upload_file",
-                                        enabled=True,
-                                        name=file_name,
-                                    )
-                                    .first()
+                            document = documents_map.get(file.name)
+                            if knowledge_config.duplicate and document:
+                                document.dataset_process_rule_id = dataset_process_rule.id
+                                document.updated_at = naive_utc_now()
+                                document.created_from = created_from
+                                document.doc_form = knowledge_config.doc_form
+                                document.doc_language = knowledge_config.doc_language
+                                document.data_source_info = json.dumps(data_source_info)
+                                document.batch = batch
+                                document.indexing_status = "waiting"
+                                db.session.add(document)
+                                documents.append(document)
+                                duplicate_document_ids.append(document.id)
+                                continue
+                            else:
+                                document = DocumentService.build_document(
+                                    dataset,
+                                    dataset_process_rule.id,
+                                    knowledge_config.data_source.info_list.data_source_type,
+                                    knowledge_config.doc_form,
+                                    knowledge_config.doc_language,
+                                    data_source_info,
+                                    created_from,
+                                    position,
+                                    account,
+                                    file.name,
+                                    batch,
                                 )
-                                if document:
-                                    document.dataset_process_rule_id = dataset_process_rule.id
-                                    document.updated_at = naive_utc_now()
-                                    document.created_from = created_from
-                                    document.doc_form = knowledge_config.doc_form
-                                    document.doc_language = knowledge_config.doc_language
-                                    document.data_source_info = json.dumps(data_source_info)
-                                    document.batch = batch
-                                    document.indexing_status = "waiting"
-                                    db.session.add(document)
-                                    documents.append(document)
-                                    duplicate_document_ids.append(document.id)
-                                    continue
-                            document = DocumentService.build_document(
-                                dataset,
-                                dataset_process_rule.id,
-                                knowledge_config.data_source.info_list.data_source_type,
-                                knowledge_config.doc_form,
-                                knowledge_config.doc_language,
-                                data_source_info,
-                                created_from,
-                                position,
-                                account,
-                                file_name,
-                                batch,
-                            )
-                            db.session.add(document)
-                            db.session.flush()
-                            document_ids.append(document.id)
-                            documents.append(document)
-                            position += 1
+                                db.session.add(document)
+                                db.session.flush()
+                                document_ids.append(document.id)
+                                documents.append(document)
+                                position += 1
                     elif knowledge_config.data_source.info_list.data_source_type == "notion_import":
                         notion_info_list = knowledge_config.data_source.info_list.notion_info_list  # type: ignore
                         if not notion_info_list: