Update extraction interface to require an Object node (#90)

The schema should always be defined with respect to an Object rather
than other
types of nodes, otherwise there is some ambiguity about when
interpreting how to
encode the object (at least when using CSV encoding).

kor/extraction.py

@@ -4,7 +4,7 @@
 from langchain.schema import BaseLanguageModel
 
 from kor.encoders import Encoder, initialize_encoder
-from kor.nodes import AbstractSchemaNode
+from kor.nodes import Object
 from kor.prompts import create_langchain_prompt
 from kor.type_descriptors import TypeDescriptor, initialize_type_descriptors
 from kor.validators import Validator
@@ -14,7 +14,7 @@
 
 def create_extraction_chain(
     llm: BaseLanguageModel,
-    node: AbstractSchemaNode,
+    node: Object,
     *,
     encoder_or_encoder_class: Union[Type[Encoder], Encoder, str] = "csv",
     type_descriptor: Union[TypeDescriptor, str] = "typescript",
@@ -36,6 +36,8 @@ def create_extraction_chain(
     Returns:
         A langchain chain
     """
+    if not isinstance(node, Object):
+        raise ValueError(f"node must be an Object got {type(node)}")
     encoder = initialize_encoder(encoder_or_encoder_class, node, **encoder_kwargs)
     type_descriptor_to_use = initialize_type_descriptors(type_descriptor)
     return LLMChain(