How to construct filters

Prerequisites

This guide assumes familiarity with the following:

• Query analysis

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 Zod schema. There is then the issue of converting that Zod schema 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.

Setup

Install dependencies

npm

npm i @langchain/core zod

yarn

yarn add @langchain/core zod

pnpm

pnpm add @langchain/core zod

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

import { z } from "zod";

const searchSchema = z.object({
  query: z.string(),
  startYear: z.number().optional(),
  author: z.string().optional(),
});

const searchQuery: z.infer<typeof searchSchema> = {
  query: "RAG",
  startYear: 2022,
  author: "LangChain",
};

import { Comparison, Comparator } from "langchain/chains/query_constructor/ir";

function constructComparisons(
  query: z.infer<typeof searchSchema>
): Comparison[] {
  const comparisons: Comparison[] = [];
  if (query.startYear !== undefined) {
    comparisons.push(
      new Comparison("gt" as Comparator, "start_year", query.startYear)
    );
  }
  if (query.author !== undefined) {
    comparisons.push(
      new Comparison("eq" as Comparator, "author", query.author)
    );
  }
  return comparisons;
}

const comparisons = constructComparisons(searchQuery);

import { Operation, Operator } from "langchain/chains/query_constructor/ir";

const _filter = new Operation("and" as Operator, comparisons);

import { ChromaTranslator } from "@langchain/community/structured_query/chroma";

new ChromaTranslator().visitOperation(_filter);

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

Next steps

You’ve now learned how to create a specific filter from an arbitrary query.

Next, check out some of the other query analysis guides in this section, like how to use few-shotting to improve performance.