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LangChain.js supports using the @vercel/postgres package to use generic Postgres databases as vector stores, provided they support the pgvector Postgres extension. This integration is particularly useful from web environments like Edge functions.

​
Setup

To work with Vercel Postgres, you need to install the @vercel/postgres package:
npm
npm install @vercel/postgres
See this section for general instructions on installing LangChain packages.
npm
npm install @langchain/community @langchain/core
This integration automatically connects using the connection string set under process.env.POSTGRES_URL. You can also pass a connection string manually like this: 
const vectorstore = await VercelPostgres.initialize(new OpenAIEmbeddings(), {
  postgresConnectionOptions: {
    connectionString:
      "postgres://<username>:<password>@<hostname>:<port>/<dbname>",
  },
});

​
Connecting to Vercel Postgres

A simple way to get started is to create a serverless Vercel Postgres instance. If you’re deploying to a Vercel project with an associated Vercel Postgres instance, the required POSTGRES_URL environment variable will already be populated in hosted environments.

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Connecting to other databases

If you prefer to host your own Postgres instance, you can use a similar flow to LangChain’s PGVector vectorstore integration and set the connection string either as an environment variable or as shown above.

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Usage

import { CohereEmbeddings } from "@langchain/cohere";
import { VercelPostgres } from "@langchain/community/vectorstores/vercel_postgres";

// Config is only required if you want to override default values.
const config = {
  // tableName: "testvercelvectorstorelangchain",
  // postgresConnectionOptions: {
  //   connectionString: "postgres://<username>:<password>@<hostname>:<port>/<dbname>",
  // },
  // columns: {
  //   idColumnName: "id",
  //   vectorColumnName: "vector",
  //   contentColumnName: "content",
  //   metadataColumnName: "metadata",
  // },
};

const vercelPostgresStore = await VercelPostgres.initialize(
  new CohereEmbeddings({ model: "embed-english-v3.0" }),
  config
);

const docHello = {
  pageContent: "hello",
  metadata: { topic: "nonsense" },
};
const docHi = { pageContent: "hi", metadata: { topic: "nonsense" } };
const docMitochondria = {
  pageContent: "Mitochondria is the powerhouse of the cell",
  metadata: { topic: "science" },
};

const ids = await vercelPostgresStore.addDocuments([
  docHello,
  docHi,
  docMitochondria,
]);

const results = await vercelPostgresStore.similaritySearch("hello", 2);
console.log(results);
/*
  [
    Document { pageContent: 'hello', metadata: { topic: 'nonsense' } },
    Document { pageContent: 'hi', metadata: { topic: 'nonsense' } }
  ]
*/

// Metadata filtering
const results2 = await vercelPostgresStore.similaritySearch(
  "Irrelevant query, metadata filtering",
  2,
  {
    topic: "science",
  }
);
console.log(results2);
/*
  [
    Document {
      pageContent: 'Mitochondria is the powerhouse of the cell',
      metadata: { topic: 'science' }
    }
  ]
*/

// Metadata filtering with IN-filters works as well
const results3 = await vercelPostgresStore.similaritySearch(
  "Irrelevant query, metadata filtering",
  3,
  {
    topic: { in: ["science", "nonsense"] },
  }
);
console.log(results3);
/*
  [
    Document {
      pageContent: 'hello',
      metadata: { topic: 'nonsense' }
    },
    Document {
      pageContent: 'hi',
      metadata: { topic: 'nonsense' }
    },
    Document {
      pageContent: 'Mitochondria is the powerhouse of the cell',
      metadata: { topic: 'science' }
    }
  ]
*/

// Upserting is supported as well
await vercelPostgresStore.addDocuments(
  [
    {
      pageContent: "ATP is the powerhouse of the cell",
      metadata: { topic: "science" },
    },
  ],
  { ids: [ids[2]] }
);

const results4 = await vercelPostgresStore.similaritySearch(
  "What is the powerhouse of the cell?",
  1
);
console.log(results4);
/*
  [
    Document {
      pageContent: 'ATP is the powerhouse of the cell',
      metadata: { topic: 'science' }
    }
  ]
*/

await vercelPostgresStore.delete({ ids: [ids[2]] });

const results5 = await vercelPostgresStore.similaritySearch(
  "No more metadata",
  2,
  {
    topic: "science",
  }
);
console.log(results5);
/*
  []
*/

// Remember to call .end() to close the connection!
await vercelPostgresStore.end();
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