multiple: langchain 0.2 in master (#21191)

0.2rc 

migrations

- [x] Move memory
- [x] Move remaining retrievers
- [x] graph_qa chains
- [x] some dependency from evaluation code potentially on math utils
- [x] Move openapi chain from `langchain.chains.api.openapi` to
`langchain_community.chains.openapi`
- [x] Migrate `langchain.chains.ernie_functions` to
`langchain_community.chains.ernie_functions`
- [x] migrate `langchain/chains/llm_requests.py` to
`langchain_community.chains.llm_requests`
- [x] Moving `langchain_community.cross_enoders.base:BaseCrossEncoder`
->
`langchain_community.retrievers.document_compressors.cross_encoder:BaseCrossEncoder`
(namespace not ideal, but it needs to be moved to `langchain` to avoid
circular deps)
- [x] unit tests langchain -- add pytest.mark.community to some unit
tests that will stay in langchain
- [x] unit tests community -- move unit tests that depend on community
to community
- [x] mv integration tests that depend on community to community
- [x] mypy checks

Other todo

- [x] Make deprecation warnings not noisy (need to use warn deprecated
and check that things are implemented properly)
- [x] Update deprecation messages with timeline for code removal (likely
we actually won't be removing things until 0.4 release) -- will give
people more time to transition their code.
- [ ] Add information to deprecation warning to show users how to
migrate their code base using langchain-cli
- [ ] Remove any unnecessary requirements in langchain (e.g., is
SQLALchemy required?)

---------

Co-authored-by: Erick Friis <erick@langchain.dev>

libs/community/langchain_community/chains/graph_qa/nebulagraph.py

@@ -0,0 +1,106 @@
+"""Question answering over a graph."""
+from __future__ import annotations
+
+from typing import Any, Dict, List, Optional
+
+from langchain.chains.base import Chain
+from langchain.chains.llm import LLMChain
+from langchain_core.callbacks import CallbackManagerForChainRun
+from langchain_core.language_models import BaseLanguageModel
+from langchain_core.prompts import BasePromptTemplate
+from langchain_core.pydantic_v1 import Field
+
+from langchain_community.chains.graph_qa.prompts import (
+    CYPHER_QA_PROMPT,
+    NGQL_GENERATION_PROMPT,
+)
+from langchain_community.graphs.nebula_graph import NebulaGraph
+
+
+class NebulaGraphQAChain(Chain):
+    """Chain for question-answering against a graph by generating nGQL statements.
+
+    *Security note*: Make sure that the database connection uses credentials
+        that are narrowly-scoped to only include necessary permissions.
+        Failure to do so may result in data corruption or loss, since the calling
+        code may attempt commands that would result in deletion, mutation
+        of data if appropriately prompted or reading sensitive data if such
+        data is present in the database.
+        The best way to guard against such negative outcomes is to (as appropriate)
+        limit the permissions granted to the credentials used with this tool.
+
+        See https://python.langchain.com/docs/security for more information.
+    """
+
+    graph: NebulaGraph = Field(exclude=True)
+    ngql_generation_chain: LLMChain
+    qa_chain: LLMChain
+    input_key: str = "query"  #: :meta private:
+    output_key: str = "result"  #: :meta private:
+
+    @property
+    def input_keys(self) -> List[str]:
+        """Return the input keys.
+
+        :meta private:
+        """
+        return [self.input_key]
+
+    @property
+    def output_keys(self) -> List[str]:
+        """Return the output keys.
+
+        :meta private:
+        """
+        _output_keys = [self.output_key]
+        return _output_keys
+
+    @classmethod
+    def from_llm(
+        cls,
+        llm: BaseLanguageModel,
+        *,
+        qa_prompt: BasePromptTemplate = CYPHER_QA_PROMPT,
+        ngql_prompt: BasePromptTemplate = NGQL_GENERATION_PROMPT,
+        **kwargs: Any,
+    ) -> NebulaGraphQAChain:
+        """Initialize from LLM."""
+        qa_chain = LLMChain(llm=llm, prompt=qa_prompt)
+        ngql_generation_chain = LLMChain(llm=llm, prompt=ngql_prompt)
+
+        return cls(
+            qa_chain=qa_chain,
+            ngql_generation_chain=ngql_generation_chain,
+            **kwargs,
+        )
+
+    def _call(
+        self,
+        inputs: Dict[str, Any],
+        run_manager: Optional[CallbackManagerForChainRun] = None,
+    ) -> Dict[str, str]:
+        """Generate nGQL statement, use it to look up in db and answer question."""
+        _run_manager = run_manager or CallbackManagerForChainRun.get_noop_manager()
+        callbacks = _run_manager.get_child()
+        question = inputs[self.input_key]
+
+        generated_ngql = self.ngql_generation_chain.run(
+            {"question": question, "schema": self.graph.get_schema}, callbacks=callbacks
+        )
+
+        _run_manager.on_text("Generated nGQL:", end="\n", verbose=self.verbose)
+        _run_manager.on_text(
+            generated_ngql, color="green", end="\n", verbose=self.verbose
+        )
+        context = self.graph.query(generated_ngql)
+
+        _run_manager.on_text("Full Context:", end="\n", verbose=self.verbose)
+        _run_manager.on_text(
+            str(context), color="green", end="\n", verbose=self.verbose
+        )
+
+        result = self.qa_chain(
+            {"question": question, "context": context},
+            callbacks=callbacks,
+        )
+        return {self.output_key: result[self.qa_chain.output_key]}