✨ feat(retrievers): add base retriever class and frontend node class

🐛 fix(util.py): handle non-string types in format_dict function
The base retriever class is added to provide a common interface for all retrievers in the language chain. The frontend node class for retrievers is also added to handle the formatting of fields specific to retrievers.

In the util.py file, a fix is made to handle non-string types in the format_dict function. Previously, if the type of a field was not a string, an error would occur. This fix ensures that the type is converted to a string before further processing.

src/backend/langflow/interface/retrievers/base.py

@@ -0,0 +1,49 @@
+from typing import Any, Dict, List, Optional, Type
+
+from langchain import retrievers
+
+from langflow.interface.base import LangChainTypeCreator
+from langflow.interface.importing.utils import import_class
+from langflow.settings import settings
+from langflow.template.frontend_node.retrievers import RetrieverFrontendNode
+from langflow.utils.logger import logger
+from langflow.utils.util import build_template_from_method
+
+
+class RetrieverCreator(LangChainTypeCreator):
+    type_name: str = "retrievers"
+
+    @property
+    def frontend_node_class(self) -> Type[RetrieverFrontendNode]:
+        return RetrieverFrontendNode
+
+    @property
+    def type_to_loader_dict(self) -> Dict:
+        if self.type_dict is None:
+            self.type_dict: dict[str, Any] = {
+                retriever_name: import_class(f"langchain.retrievers.{retriever_name}")
+                for retriever_name in retrievers.__all__
+            }
+        return self.type_dict
+
+    def get_signature(self, name: str) -> Optional[Dict]:
+        """Get the signature of an embedding."""
+        try:
+            return build_template_from_method(
+                name, type_to_cls_dict=self.type_to_loader_dict, method_name="from_llm"
+            )
+        except ValueError as exc:
+            raise ValueError(f"Retriever {name} not found") from exc
+        except AttributeError as exc:
+            logger.error(f"Retriever {name} not loaded: {exc}")
+            return None
+
+    def to_list(self) -> List[str]:
+        return [
+            retriever
+            for retriever in self.type_to_loader_dict.keys()
+            if retriever in settings.retrievers or settings.dev
+        ]
+
+
+retriever_creator = RetrieverCreator()

src/backend/langflow/template/frontend_node/retrievers.py

@@ -0,0 +1,15 @@
+from typing import Optional
+
+from langflow.template.field.base import TemplateField
+from langflow.template.frontend_node.base import FrontendNode
+
+
+class RetrieverFrontendNode(FrontendNode):
+    @staticmethod
+    def format_field(field: TemplateField, name: Optional[str] = None) -> None:
+        FrontendNode.format_field(field, name)
+        # Define common field attributes
+        field.show = True
+        if field.name == "parser_key":
+            field.display_name = "Parser Key"
+            field.password = False

src/backend/langflow/utils/util.py

@@ -233,6 +233,9 @@ def format_dict(d, name: Optional[str] = None):
 
         _type = value["type"]
 
+        if not isinstance(_type, str):
+            _type = _type.__name__
+
         # Remove 'Optional' wrapper
         if "Optional" in _type:
             _type = _type.replace("Optional[", "")[:-1]