feat: Support for database backend Task Store

[kthota-g]

Release-As: 0.2.11

Add support for database backed TaskStore

Installation

uv add a2a-sdk[postgresql] #postgres driver
or 
uv add a2a-sdk[mysql] #mysql driver
or
uv add a2a-sdk[sqlite] #sqlite driver
or
uv add a2a-sdk[sql]. #install all three sql drivers

Usage

from a2a.server.tasks import DatabaseTaskStore
from sqlalchemy.ext.asyncio import (
        create_async_engine,
    )
...
...
# Postgres - "postgresql+asyncpg://postgres:postgres@localhost:5432/a2a_test"
# Sqlite - "sqlite+aiosqlite:///file::memory:?cache=shared"
# Mysql - "mysql+aiomysql://admin:saysoyeah@localhost:3306/testDB"
engine = create_async_engine(
    "postgresql+asyncpg://postgres:postgres@localhost:5432/a2a_test", echo=False
)
request_handler = DefaultRequestHandler(
    agent_executor=CurrencyAgentExecutor(),
    task_store=DatabaseTaskStore(engine=engine),
    push_notifier=InMemoryPushNotifier(httpx_client),
)

[gemini-code-assist]

Summary of Changes

Hello @kthota-g, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request significantly enhances the A2A SDK by introducing robust, database-backed persistence for task management. It moves beyond ephemeral in-memory storage, allowing task states, artifacts, and history to be reliably stored and retrieved from various SQL databases. This change provides a foundational improvement for building more resilient and scalable applications.

Highlights

• New Feature: Database Task Store: I've introduced a new DatabaseTaskStore implementation that allows for persistent storage of task objects using SQLAlchemy. This replaces the previous in-memory storage, enabling tasks to survive application restarts and be shared across instances.
• Multi-Database Support: The DatabaseTaskStore supports PostgreSQL, MySQL, and SQLite, leveraging SQLAlchemy's async capabilities. Users can select their preferred database by installing the corresponding optional dependencies (e.g., a2a-sdk[postgresql]).
• Pydantic Model Serialization: Custom SQLAlchemy TypeDecorators (PydanticType and PydanticListType) have been added to automatically serialize and deserialize Pydantic models (like TaskStatus, Artifact, Message) to and from JSON columns in the database, simplifying data handling.
• Installation & Usage Documentation: The README.md has been updated to include clear instructions for installing the SDK with database support using uv or pip, and the PR description provides Python code examples for initializing the DatabaseTaskStore with different database engines.
• Development & Testing Infrastructure: A Docker Compose setup for PostgreSQL has been added (docker/postgres/docker-compose.yml, docker/postgres/init.sql) to facilitate local development and testing. Comprehensive asynchronous unit tests for the DatabaseTaskStore have been implemented, covering various CRUD operations and data types across SQLite, PostgreSQL, and MySQL.

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[gemini-code-assist]

Code Review

This pull request introduces a database-backed TaskStore using SQLAlchemy. The code is well-structured, and the addition of comprehensive, parameterized tests is excellent. The feedback focuses on refactoring the save method in DatabaseTaskStore to use session.merge() and cleaning up the database initialization script and test fixtures.