langchain-postgres

The langchain-postgres package implementations of core LangChain abstractions using Postgres.

The package is released under the MIT license.

Feel free to use the abstraction as provided or else modify them / extend them as appropriate for your own application.

Requirements

The package supports the asyncpg and psycopg3 drivers.

Installation

pip install -U langchain-postgres

Vectorstore

Warning

In v0.0.14+, PGVector is deprecated. Please migrate to PGVectorStore for improved performance and manageability. See the migration guide for details on how to migrate from PGVector to PGVectorStore.

Documentation

• Quickstart
• How-to

Tip

For developing, debugging, and deploying AI agents and LLM applications, see LangSmith.

Example

from langchain_core.documents import Document
from langchain_core.embeddings import DeterministicFakeEmbedding
from langchain_postgres import PGEngine, PGVectorStore

# Replace the connection string with your own Postgres connection string
CONNECTION_STRING = "postgresql+psycopg://langchain:langchain@localhost:6024/langchain"
engine = PGEngine.from_connection_string(url=CONNECTION_STRING)

# Replace the vector size with your own vector size
VECTOR_SIZE = 768
embedding = DeterministicFakeEmbedding(size=VECTOR_SIZE)

TABLE_NAME = "my_doc_collection"

engine.init_vectorstore_table(
    table_name=TABLE_NAME,
    vector_size=VECTOR_SIZE,
)

store = PGVectorStore.create_sync(
    engine=engine,
    table_name=TABLE_NAME,
    embedding_service=embedding,
)

docs = [
    Document(page_content="Apples and oranges"),
    Document(page_content="Cars and airplanes"),
    Document(page_content="Train")
]

store.add_documents(docs)

query = "I'd like a fruit."
docs = store.similarity_search(query)
print(docs)

Tip

All synchronous functions have corresponding asynchronous functions

Hybrid Search with PGVectorStore

With PGVectorStore you can use hybrid search for more comprehensive and relevant search results.

vs = PGVectorStore.create_sync(
    engine=engine,
    table_name=TABLE_NAME,
    embedding_service=embedding,
    hybrid_search_config=HybridSearchConfig(
      fusion_function=reciprocal_rank_fusion
    ),
)
hybrid_docs = vector_store.similarity_search("products", k=5)

For a detailed guide on how to use hybrid search, see the documentation.

ChatMessageHistory

The chat message history abstraction helps to persist chat message history in a postgres table.

PostgresChatMessageHistory is parameterized using a table_name and a session_id.

The table_name is the name of the table in the database where the chat messages will be stored.

The session_id is a unique identifier for the chat session. It can be assigned by the caller using uuid.uuid4().

import uuid

from langchain_core.messages import SystemMessage, AIMessage, HumanMessage
from langchain_postgres import PostgresChatMessageHistory
import psycopg

# Establish a synchronous connection to the database
# (or use psycopg.AsyncConnection for async)
conn_info = ... # Fill in with your connection info
sync_connection = psycopg.connect(conn_info)

# Create the table schema (only needs to be done once)
table_name = "chat_history"
PostgresChatMessageHistory.create_tables(sync_connection, table_name)

session_id = str(uuid.uuid4())

# Initialize the chat history manager
chat_history = PostgresChatMessageHistory(
    table_name,
    session_id,
    sync_connection=sync_connection
)

# Add messages to the chat history
chat_history.add_messages([
    SystemMessage(content="Meow"),
    AIMessage(content="woof"),
    HumanMessage(content="bark"),
])

print(chat_history.messages)

Google Cloud Integrations

Google Cloud provides Vector Store, Chat Message History, and Data Loader integrations for AlloyDB and Cloud SQL for PostgreSQL databases via the following PyPi packages:

• langchain-google-alloydb-pg

• langchain-google-cloud-sql-pg

Using the Google Cloud integrations provides the following benefits:

• Enhanced Security: Securely connect to Google Cloud databases utilizing IAM for authorization and database authentication without needing to manage SSL certificates, configure firewall rules, or enable authorized networks.
• Simplified and Secure Connections: Connect to Google Cloud databases effortlessly using the instance name instead of complex connection strings. The integrations creates a secure connection pool that can be easily shared across your application using the engine object.

Vector Store	Metadata filtering	Async support	Schema Flexibility	Improved metadata handling	Hybrid Search
Google AlloyDB	✓	✓	✓	✓	✗
Google Cloud SQL Postgres	✓	✓	✓	✓	✗