🔧 chore(loading.py): add support for instantiating retrievers in the initialization process

🚀 feat(loading.py): implement the ability to instantiate retrievers based on node type and class object
The `instantiate_based_on_type` function now includes a new condition to handle the instantiation of retrievers. The `instantiate_retriever` function is introduced to handle the specific logic for creating retrievers. This change allows for the dynamic creation of retrievers based on the provided node type and class object.

src/backend/langflow/interface/initialize/loading.py

@@ -15,6 +15,7 @@ from langflow.interface.custom_lists import CUSTOM_NODES
 from langflow.interface.importing.utils import get_function, import_by_type
 from langflow.interface.toolkits.base import toolkits_creator
 from langflow.interface.chains.base import chain_creator
+from langflow.interface.retrievers.base import retriever_creator
 from langflow.interface.utils import load_file_into_dict
 from langflow.utils import validate
 from langchain.chains.base import Chain
@@ -79,10 +80,23 @@ def instantiate_based_on_type(class_object, base_type, node_type, params):
         return instantiate_chains(node_type, class_object, params)
     elif base_type == "llms":
         return instantiate_llm(node_type, class_object, params)
+    elif base_type == "retrievers":
+        return instantiate_retriever(node_type, class_object, params)
     else:
         return class_object(**params)
 
 
+def instantiate_retriever(node_type, class_object, params):
+    if "retriever" in params and hasattr(params["retriever"], "as_retriever"):
+        params["retriever"] = params["retriever"].as_retriever()
+    if node_type in retriever_creator.from_method_nodes:
+        method = retriever_creator.from_method_nodes[node_type]
+        if class_method := getattr(class_object, method, None):
+            return class_method(**params)
+        raise ValueError(f"Method {method} not found in {class_object}")
+    return class_object(**params)
+
+
 def instantiate_llm(node_type, class_object, params: Dict):
     return class_object(**params)