langchain-postgres: Initial package with postgres chat history implem…

…entation (langchain-ai#19884)

- [x] Add in code examples for the chat message history class
- [ ] ~Add docs with notebook examples~ (can this be done later?)
- [x] Update README.md

libs/partners/postgres/LICENSE

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+MIT License
+
+Copyright (c) 2024 LangChain, Inc.
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

libs/partners/postgres/Makefile

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+.PHONY: all format lint test tests integration_tests docker_tests help extended_tests
+
+# Default target executed when no arguments are given to make.
+all: help
+
+# Define a variable for the test file path.
+TEST_FILE ?= tests/unit_tests/
+integration_test integration_tests: TEST_FILE = tests/integration_tests/
+
+test tests integration_test integration_tests:
+	poetry run pytest $(TEST_FILE)
+
+######################
+# LINTING AND FORMATTING
+######################
+
+# Define a variable for Python and notebook files.
+PYTHON_FILES=.
+MYPY_CACHE=.mypy_cache
+lint format: PYTHON_FILES=.
+lint_diff format_diff: PYTHON_FILES=$(shell git diff --relative=libs/partners/postgres --name-only --diff-filter=d master | grep -E '\.py$$|\.ipynb$$')
+lint_package: PYTHON_FILES=langchain_postgres
+lint_tests: PYTHON_FILES=tests
+lint_tests: MYPY_CACHE=.mypy_cache_test
+
+lint lint_diff lint_package lint_tests:
+	poetry run ruff .
+	poetry run ruff format $(PYTHON_FILES) --diff
+	poetry run ruff --select I $(PYTHON_FILES)
+	mkdir -p $(MYPY_CACHE); poetry run mypy $(PYTHON_FILES) --cache-dir $(MYPY_CACHE)
+
+format format_diff:
+	poetry run ruff format $(PYTHON_FILES)
+	poetry run ruff --select I --fix $(PYTHON_FILES)
+
+spell_check:
+	poetry run codespell --toml pyproject.toml
+
+spell_fix:
+	poetry run codespell --toml pyproject.toml -w
+
+check_imports: $(shell find langchain_postgres -name '*.py')
+	poetry run python ./scripts/check_imports.py $^
+
+######################
+# HELP
+######################
+
+help:
+	@echo '----'
+	@echo 'check_imports				- check imports'
+	@echo 'format                       - run code formatters'
+	@echo 'lint                         - run linters'
+	@echo 'test                         - run unit tests'
+	@echo 'tests                        - run unit tests'
+	@echo 'test TEST_FILE=<test_file>   - run all tests in file'

libs/partners/postgres/README.md

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+# langchain-postgres
+
+The `langchain-postgres` package is an integration package managed by the core LangChain team.
+
+This package contains implementations of core 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.
+
+## Installation
+
+```bash
+pip install -U langchain-postgres
+```
+
+## Usage
+
+### 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()`.
+
+```python
+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_schema(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)
+```

libs/partners/postgres/langchain_postgres/__init__.py

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+from importlib import metadata
+
+from langchain_postgres.chat_message_histories import PostgresChatMessageHistory
+
+try:
+    __version__ = metadata.version(__package__)
+except metadata.PackageNotFoundError:
+    # Case where package metadata is not available.
+    __version__ = ""
+
+__all__ = [
+    "__version__",
+    "PostgresChatMessageHistory",
+]