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Mapping values to database

In this guide we’ll go over strategies to improve graph database query generation by mapping values from user inputs to database. When using the built-in graph chains, the LLM is aware of the graph schema, but has no information about the values of properties stored in the database. Therefore, we can introduce a new step in graph database QA system to accurately map values.

Setup​

Install dependencies​

tip

See this section for general instructions on installing integration packages.

yarn add langchain @langchain/community @langchain/openai neo4j-driver zod

Set environment variables​

We’ll use OpenAI in this example:

OPENAI_API_KEY=your-api-key

# Optional, use LangSmith for best-in-class observability
LANGSMITH_API_KEY=your-api-key
LANGCHAIN_TRACING_V2=true

Next, we need to define Neo4j credentials. Follow these installation steps to set up a Neo4j database.

NEO4J_URI="bolt://localhost:7687"
NEO4J_USERNAME="neo4j"
NEO4J_PASSWORD="password"

The below example will create a connection with a Neo4j database and will populate it with example data about movies and their actors.

import "neo4j-driver";
import { Neo4jGraph } from "@langchain/community/graphs/neo4j_graph";

const url = Deno.env.get("NEO4J_URI");
const username = Deno.env.get("NEO4J_USER");
const password = Deno.env.get("NEO4J_PASSWORD");
const graph = await Neo4jGraph.initialize({ url, username, password });

// Import movie information
const moviesQuery = `LOAD CSV WITH HEADERS FROM 
'https://raw.githubusercontent.com/tomasonjo/blog-datasets/main/movies/movies_small.csv'
AS row
MERGE (m:Movie {id:row.movieId})
SET m.released = date(row.released),
    m.title = row.title,
    m.imdbRating = toFloat(row.imdbRating)
FOREACH (director in split(row.director, '|') | 
    MERGE (p:Person {name:trim(director)})
    MERGE (p)-[:DIRECTED]->(m))
FOREACH (actor in split(row.actors, '|') | 
    MERGE (p:Person {name:trim(actor)})
    MERGE (p)-[:ACTED_IN]->(m))
FOREACH (genre in split(row.genres, '|') | 
    MERGE (g:Genre {name:trim(genre)})
    MERGE (m)-[:IN_GENRE]->(g))`;

await graph.query(moviesQuery);
Schema refreshed successfully.
[]

Detecting entities in the user input​

We have to extract the types of entities/values we want to map to a graph database. In this example, we are dealing with a movie graph, so we can map movies and people to the database.

import { ChatPromptTemplate } from "@langchain/core/prompts";
import { ChatOpenAI } from "@langchain/openai";
import { z } from "zod";

const llm = new ChatOpenAI({ model: "gpt-3.5-turbo", temperature: 0 });

const entities = z
  .object({
    names: z
      .array(z.string())
      .describe("All the person or movies appearing in the text"),
  })
  .describe("Identifying information about entities.");

const prompt = ChatPromptTemplate.fromMessages([
  ["system", "You are extracting person and movies from the text."],
  [
    "human",
    "Use the given format to extract information from the following\ninput: {question}",
  ],
]);

const entityChain = prompt.pipe(llm.withStructuredOutput(entities));

We can test the entity extraction chain.

const entities = await entityChain.invoke({
  question: "Who played in Casino movie?",
});
entities;
{ names: [ "Casino" ] }

We will utilize a simple CONTAINS clause to match entities to database. In practice, you might want to use a fuzzy search or a fulltext index to allow for minor misspellings.

const matchQuery = `
MATCH (p:Person|Movie)
WHERE p.name CONTAINS $value OR p.title CONTAINS $value
RETURN coalesce(p.name, p.title) AS result, labels(p)[0] AS type
LIMIT 1`;

const matchToDatabase = async (values) => {
  let result = "";
  for (const entity of values.names) {
    const response = await graph.query(matchQuery, {
      value: entity,
    });
    if (response.length > 0) {
      result += `${entity} maps to ${response[0]["result"]} ${response[0]["type"]} in database\n`;
    }
  }
  return result;
};

await matchToDatabase(entities);
"Casino maps to Casino Movie in database\n"

Custom Cypher generating chain​

We need to define a custom Cypher prompt that takes the entity mapping information along with the schema and the user question to construct a Cypher statement. We will be using the LangChain expression language to accomplish that.

import { StringOutputParser } from "@langchain/core/output_parsers";
import {
  RunnablePassthrough,
  RunnableSequence,
} from "@langchain/core/runnables";

// Generate Cypher statement based on natural language input
const cypherTemplate = `Based on the Neo4j graph schema below, write a Cypher query that would answer the user's question:
{schema}
Entities in the question map to the following database values:
{entities_list}
Question: {question}
Cypher query:`;

const cypherPrompt = ChatPromptTemplate.fromMessages([
  [
    "system",
    "Given an input question, convert it to a Cypher query. No pre-amble.",
  ],
  ["human", cypherTemplate],
]);

const llmWithStop = llm.bind({ stop: ["\nCypherResult:"] });

const cypherResponse = RunnableSequence.from([
  RunnablePassthrough.assign({ names: entityChain }),
  RunnablePassthrough.assign({
    entities_list: async (x) => matchToDatabase(x.names),
    schema: async (_) => graph.getSchema(),
  }),
  cypherPrompt,
  llmWithStop,
  new StringOutputParser(),
]);
const cypher = await cypherResponse.invoke({
  question: "Who played in Casino movie?",
});
cypher;
'MATCH (:Movie {title: "Casino"})<-[:ACTED_IN]-(actor)\nRETURN actor.name'

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