Database Integration — JustAPI Docs

JustAPI provides a built-in database connection pool manager (app.db) that executes queries in Rust via sqlx, keeping the GIL released for maximum throughput.

Quick Start: SQLite

from justapi import JustAPIApp

app = JustAPIApp()

app.set_database(
    "sqlite:///app.db",
    init_sql="""
    CREATE TABLE IF NOT EXISTS items (
        id INTEGER PRIMARY KEY AUTOINCREMENT,
        name TEXT NOT NULL,
        quantity INTEGER DEFAULT 0
    )
    """,
)


@app.get("/items")
def list_items(request):
    return app.db.query("SELECT * FROM items ORDER BY id")


@app.post("/items")
def add_item(request):
    data = request.json()
    app.db.execute(
        "INSERT INTO items (name, quantity) VALUES ($1, $2)",
        [data["name"], data.get("quantity", 0)],
    )
    return {"message": "Item created"}

Supported Databases

Engine	URL Scheme	Driver	Use Case
PostgreSQL	`postgres://user:pass@host/db`	Rust `sqlx-postgres`	Production OLTP
MySQL	`mysql://user:pass@host/db`	Rust `sqlx-mysql`	Scalable relational
SQLite	`sqlite:///path/to/db.db`	Rust `sqlx-sqlite`	Embedded, dev, single-server
DuckDB	`duckdb:///path/to/db.duckdb`	Python `duckdb`	Analytical OLAP
ClickHouse	`clickhouse://host:9000/db`	Python `clickhouse-driver`	Column-store analytics
MongoDB	`mongodb://host:27017/db`	Python `pymongo`	Document store
Redis	`redis://host:6379/0`	Python `redis`	Caching, pub/sub

PostgreSQL Example

app.set_database(
    "postgres://postgres:password@localhost:5432/mydb",
    init_sql="""
    CREATE TABLE IF NOT EXISTS users (
        id SERIAL PRIMARY KEY,
        name TEXT NOT NULL,
        email TEXT UNIQUE NOT NULL
    )
    """,
)


@app.post("/users")
def create_user(request):
    data = request.json()
    result = app.db.query(
        "INSERT INTO users (name, email) VALUES ($1, $2) RETURNING id",
        [data["name"], data["email"]],
    )
    return {"user_id": result[0]["id"]}

Query API

The app.db object provides two methods:

Method	Description	Returns
`app.db.query(sql, params)`	Execute a SELECT query	`list[dict]` — rows as dicts
`app.db.execute(sql, params)`	Execute INSERT/UPDATE/DELETE	`int` — affected rows

Connection Pool Configuration

app.set_database(
    "postgres://localhost/mydb",
    max_connections=20,                # Pool size (default: 10)
    request_acquire_timeout=3.0,       # Seconds before 503 (default: 3.0)
    init_sql="CREATE TABLE IF NOT EXISTS ...",
)

SQLite-Specific Options

app.set_database(
    "sqlite:///app.db",
    wal=True,                           # Enable WAL mode for concurrent access
    pragmas=["journal_mode=WAL", "synchronous=NORMAL"],
)

By default, JustAPI enables busy_timeout=5000, WAL journal mode, and synchronous=NORMAL for all SQLite connections to support concurrent reads and writes.

Pool Saturation Handling

When the connection pool is exhausted, requests get 503 Service Unavailable instead of waiting indefinitely:

# Default: request_acquire_timeout=3.0 seconds
# If no connection is available within 3s, returns 503
app.set_database("sqlite:///app.db", request_acquire_timeout=1.0)

Migration System

JustAPI includes a simple migration runner:

justapi db migrate    # Apply pending migrations
justapi db rollback   # Rollback last migration
justapi db list       # List migration status

Migrations are SQL files in the migrations/ directory:

-- migrations/0002_add_email.sql
ALTER TABLE users ADD COLUMN email TEXT;

Using Native Drivers (Python)

For databases not supported by sqlx, use standard Python drivers:

import duckdb


app = JustAPIApp()
conn = duckdb.connect("analytics.duckdb")


@app.get("/analytics/sales")
def sales_summary(request):
    result = conn.execute(
        "SELECT region, SUM(amount) as total FROM sales GROUP BY region"
    ).fetchall()
    return {"summary": [{"region": r[0], "total": r[1]} for r in result]}

How It Works Internally

app.set_database() creates a Rust sqlx connection pool (AnyPool)
Queries are executed in Rust via py.detach() — zero GIL overhead
Results are returned as Python dicts via zero-copy serialization
Transactions are auto-managed: commit on 2xx, rollback on error
Pool saturation returns 503 with Retry-After: 1 header

Next Steps

Background Tasks — Async processing after DB writes
Dependency Injection — DB session as a dependency
Performance Tuning — Optimize database queries

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