adds example for pgvector search with metadata (#947)

Author: sergiobayona

examples/store_and_query_with_pgvector_using_metadata.rb

@@ -0,0 +1,75 @@
+# frozen_string_literal: true
+
+require "langchain"
+require "dotenv/load"
+require "ruby/openai"
+
+# Initialize the Pgvector client
+pgvector = Langchain::Vectorsearch::Pgvector.new(
+  url: ENV["POSTGRES_URL"],
+  index_name: "documents",
+  llm: Langchain::LLM::OpenAI.new(api_key: ENV["OPENAI_API_KEY"])
+)
+
+# Create the default schema if it doesn't exist
+pgvector.create_default_schema
+
+# Add documents with metadata
+documents = [
+  {
+    text: "The quick brown fox jumps over the lazy dog",
+    metadata: {
+      source: "fables",
+      author: "Aesop",
+      category: "animals"
+    }
+  },
+  {
+    text: "To be or not to be, that is the question",
+    metadata: {
+      source: "hamlet",
+      author: "Shakespeare",
+      category: "drama"
+    }
+  },
+  {
+    text: "It was the best of times, it was the worst of times",
+    metadata: {
+      source: "tale_of_two_cities",
+      author: "Dickens",
+      category: "novel"
+    }
+  }
+]
+
+# Add texts with metadata
+ids = pgvector.add_texts(
+  texts: documents.map { |doc| doc[:text] },
+  metadata: documents.map { |doc| doc[:metadata] }
+)
+
+puts "Added documents with IDs: #{ids.inspect}"
+
+# Perform a similarity search
+puts "\nSearching for documents similar to 'fox':"
+results = pgvector.similarity_search(query: "fox", k: 2)
+results.each do |result|
+  puts "Content: #{result.content}"
+  puts "Metadata: #{JSON.parse(result.metadata)}"
+  puts "---"
+end
+
+# Search with specific metadata filter
+puts "\nSearching for Shakespeare's works:"
+results = pgvector.similarity_search(query: "drama", k: 1)
+results.each do |result|
+  metadata = JSON.parse(result.metadata)
+  if metadata["author"] == "Shakespeare"
+    puts "Found Shakespeare's work:"
+    puts "Content: #{result.content}"
+    puts "Metadata: #{metadata}"
+  end
+end
+
+# Clean up (optional)
+# pgvector.destroy_default_schema