Serialize all the chains! (#761)

Co-authored-by: Harrison Chase <hw.chase.17@gmail.com>

langchain/chains/sql_database/base.py

@@ -3,7 +3,7 @@ from __future__ import annotations
 
 from typing import Any, Dict, List
 
-from pydantic import BaseModel, Extra
+from pydantic import BaseModel, Extra, Field
 
 from langchain.chains.base import Chain
 from langchain.chains.llm import LLMChain
@@ -26,7 +26,7 @@ class SQLDatabaseChain(Chain, BaseModel):
 
     llm: BaseLLM
     """LLM wrapper to use."""
-    database: SQLDatabase
+    database: SQLDatabase = Field(exclude=True)
     """SQL Database to connect to."""
     prompt: BasePromptTemplate = PROMPT
     """Prompt to use to translate natural language to SQL."""
@@ -84,6 +84,10 @@ class SQLDatabaseChain(Chain, BaseModel):
         self.callback_manager.on_text(final_result, color="green", verbose=self.verbose)
         return {self.output_key: final_result}
 
+    @property
+    def _chain_type(self) -> str:
+        return "sql_database_chain"
+
 
 class SQLDatabaseSequentialChain(Chain, BaseModel):
     """Chain for querying SQL database that is a sequential chain.
@@ -153,3 +157,7 @@ class SQLDatabaseSequentialChain(Chain, BaseModel):
             "table_names_to_use": table_names_to_use,
         }
         return self.sql_chain(new_inputs, return_only_outputs=True)
+
+    @property
+    def _chain_type(self) -> str:
+        return "sql_database_sequential_chain"