How-To Add Recommendations to a Rails App with pgvector and OpenAI

While creating The AI Job Network, I wanted to show similar job recommendations when the user sees a job post. Building it is straightforward, using pgvector, ruby-openai, and the neighbor gem.

Your PostgreSQL server needs to support pgvector. Install your own or pick a hosted provider.

Install necessary gems

First, add the ruby-openai and Neighbor gems to your Gemfile:

gem "neighbor"
gem "ruby-openai"

Then, run bundle install:

bundle install

Enable pgvector in PostgreSQL

In a Rails migration, include:

class EnablePgVector < ActiveRecord::Migration[7.0]
  def change
    enable_extension "vector"
  end
end

Setup your model

Create a vector column to store the embedding:

class AddNeighborVectorToJobs < ActiveRecord::Migration[7.0]
  def change
    add_column :jobs, :embedding, :vector, limit: 1536
  end
end

Add neighbors to your model and use OpenAI’s embedding model to create the vector embedding. Here I’m generating the embedding in a callback, but you probably want to do it in a background job.

class Job < ApplicationRecord
  has_neighbors :embedding

  after_validation :generate_vector_embed

  def embed_input
    <<~EOS
      Title: #{title}
      Category: #{category}
      Keywords: #{keywords}
    EOS
  end

  private
  def generate_vector_embed
    client = OpenAI::Client.new
    response = client.embeddings(
      parameters: {
        model: "text-embedding-ada-002",
        input: embed_input,
      },
    )
    self.embedding = response.dig("data", 0, "embedding")
  end
end

Getting Recommendations

You can get similar records from any item with nearest_neighbors and check their similarity with neighbor_distance.

job = Job.first
job.nearest_neighbors(:embedding, distance: "inner_product").first(3).each do | job|
  puts "#{job.title} - #{job.neighbor_distance}"
end

Showing similar job posts

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