Construct Filters

We may want to do query analysis to extract filters to pass into retrievers. One way we ask the LLM to represent these filters is as a Pydantic model. There is then the issue of converting that Pydantic model into a filter that can be passed into a retriever.

This can be done manually, but LangChain also provides some “Translators” that are able to translate from a common syntax into filters specific to each retriever. Here, we will cover how to use those translators.

from typing import Optional

from langchain.chains.query_constructor.ir import (
    Comparator,
    Comparison,
    Operation,
    Operator,
    StructuredQuery,
)
from langchain.retrievers.self_query.chroma import ChromaTranslator
from langchain.retrievers.self_query.elasticsearch import ElasticsearchTranslator
from langchain_core.pydantic_v1 import BaseModel

API Reference:

• Comparator
• Comparison
• Operation
• Operator
• StructuredQuery
• ChromaTranslator
• ElasticsearchTranslator

In this example, year and author are both attributes to filter on.

class Search(BaseModel):
    query: str
    start_year: Optional[int]
    author: Optional[str]

search_query = Search(query="RAG", start_year=2022, author="LangChain")

def construct_comparisons(query: Search):
    comparisons = []
    if query.start_year is not None:
        comparisons.append(
            Comparison(
                comparator=Comparator.GT,
                attribute="start_year",
                value=query.start_year,
            )
        )
    if query.author is not None:
        comparisons.append(
            Comparison(
                comparator=Comparator.EQ,
                attribute="author",
                value=query.author,
            )
        )
    return comparisons

comparisons = construct_comparisons(search_query)

_filter = Operation(operator=Operator.AND, arguments=comparisons)

ElasticsearchTranslator().visit_operation(_filter)

{'bool': {'must': [{'range': {'metadata.start_year': {'gt': 2022}}},
   {'term': {'metadata.author.keyword': 'LangChain'}}]}}

ChromaTranslator().visit_operation(_filter)

{'$and': [{'start_year': {'$gt': 2022}}, {'author': {'$eq': 'LangChain'}}]}