PostgreSQL Database Setup Pattern

This skill helps you set up a PostgreSQL database following a standardized pattern with proper separation of schema and setup scripts.

When to Use This Skill

Use this skill when:

• Starting a new project that needs PostgreSQL
• You want a clean separation between schema definition (SQL) and setup logic (Python)
• You need support for both production and test databases
• You want consistent environment variable patterns

What This Skill Creates

1. database/schema.sql - SQL schema with table definitions
2. dev_scripts/setup_database.py - Python setup script
3. Documentation of required environment variables

Step 1: Gather Project Information

IMPORTANT: Before creating files, ask the user these questions:

1. "What is your project name?" (e.g., "arcana", "trading-bot", "myapp")

   • Use this to derive:
     • Database name: {project_name} (e.g., arcana)
     • User name: {project_name} (e.g., arcana)
     • Password env var: {PROJECT_NAME}_PG_PASSWORD (e.g., ARCANA_PG_PASSWORD)

2. "What tables do you need in your schema?" (optional - can create skeleton if unknown)

Step 2: Create Directory Structure

Create these directories if they don't exist:

{project_root}/
├── database/
└── dev_scripts/

Step 3: Create schema.sql

Create database/schema.sql with:

Best Practices to Follow:

• Use CREATE TABLE IF NOT EXISTS for idempotency
• Use UUID for primary keys with gen_random_uuid() as default
• Use BIGINT (Unix timestamps) for all date/time fields (NOT TIMESTAMP, NOT TIMESTAMPTZ)
• Add proper foreign key constraints with ON DELETE CASCADE or ON DELETE SET NULL
• Add indexes on foreign keys and commonly queried fields
• Use TEXT instead of VARCHAR (PostgreSQL best practice)
• Add comments using COMMENT ON COLUMN for documentation

Template Structure:

-- Enable required extensions
CREATE EXTENSION IF NOT EXISTS pgcrypto;

-- Example table
CREATE TABLE IF NOT EXISTS example_table (
    id UUID PRIMARY KEY DEFAULT gen_random_uuid(),
    name TEXT NOT NULL,
    created_at BIGINT NOT NULL DEFAULT extract(epoch from now())::bigint,
    updated_at BIGINT
);

-- Add indexes
CREATE INDEX IF NOT EXISTS idx_example_created_at ON example_table(created_at);

-- Add comments
COMMENT ON TABLE example_table IS 'Description of what this table stores';
COMMENT ON COLUMN example_table.created_at IS 'Unix timestamp of creation';

If user provides specific tables, create schema accordingly. Otherwise, create a skeleton with one example table.

Step 4: Create setup_database.py

Create dev_scripts/setup_database.py using this template, substituting project-specific values:

#!/usr/bin/env python
"""
Database setup script for {PROJECT_NAME}
Creates the {project_name} database and user with proper permissions, then applies database/schema.sql

Usage:
  python setup_database.py --pg-password <postgres_password>
  python setup_database.py --pg-password <postgres_password> --pg-user <superuser>
  python setup_database.py --pg-password <postgres_password> --test-db
"""

import os
import sys
import argparse
import psycopg2
from psycopg2.extensions import ISOLATION_LEVEL_AUTOCOMMIT


def main():
    """Setup {project_name} database and user"""
    parser = argparse.ArgumentParser(description='Setup {PROJECT_NAME} database')
    parser.add_argument('--pg-password', required=True,
                       help='PostgreSQL superuser password (required)')
    parser.add_argument('--pg-user', default='postgres',
                       help='PostgreSQL superuser name (default: postgres)')
    parser.add_argument('--test-db', action='store_true',
                       help='Create {project_name}_test database instead of main {project_name} database')
    args = parser.parse_args()

    pg_host = os.environ.get('POSTGRES_HOST', 'localhost')
    pg_port = os.environ.get('POSTGRES_PORT', '5432')
    pg_user = args.pg_user
    pg_password = args.pg_password

    if args.test_db:
        {project_name}_db = '{project_name}_test'
        print("Setting up TEST database '{project_name}_test'...")
    else:
        {project_name}_db = os.environ.get('{PROJECT_NAME}_PG_DB', '{project_name}')
    {project_name}_user = os.environ.get('{PROJECT_NAME}_PG_USER', '{project_name}')
    {project_name}_password = os.environ.get('{PROJECT_NAME}_PG_PASSWORD', None)

    if {project_name}_password is None:
        print("Error: {PROJECT_NAME}_PG_PASSWORD environment variable is required")
        sys.exit(1)

    print(f"Setting up database '{{project_name}_db}' and user '{{project_name}_user}'...")
    print(f"Connecting to PostgreSQL at {pg_host}:{pg_port} as {pg_user}")

    try:
        conn = psycopg2.connect(
            host=pg_host,
            port=pg_port,
            database='postgres',
            user=pg_user,
            password=pg_password
        )
        conn.set_isolation_level(ISOLATION_LEVEL_AUTOCOMMIT)

        with conn.cursor() as cursor:
            cursor.execute("SELECT 1 FROM pg_roles WHERE rolname = %s", ({project_name}_user,))
            if not cursor.fetchone():
                print(f"Creating user '{{project_name}_user}'...")
                cursor.execute(f"CREATE USER {project_name}_user WITH PASSWORD %s", ({project_name}_password,))
                print(f"✓ User '{{project_name}_user}' created")
            else:
                print(f"✓ User '{{project_name}_user}' already exists")

            cursor.execute("SELECT 1 FROM pg_database WHERE datname = %s", ({project_name}_db,))
            if not cursor.fetchone():
                print(f"Creating database '{{project_name}_db}'...")
                cursor.execute(f"CREATE DATABASE {{project_name}_db} OWNER {{project_name}_user}")
                print(f"✓ Database '{{project_name}_db}' created")
            else:
                print(f"✓ Database '{{project_name}_db}' already exists")

            print("Setting permissions...")
            cursor.execute(f"GRANT ALL PRIVILEGES ON DATABASE {{project_name}_db} TO {{project_name}_user}")
            print(f"✓ Granted all privileges on database '{{project_name}_db}' to user '{{project_name}_user}'")

        conn.close()

        print(f"\\nConnecting as '{{project_name}_user}' to apply schema...")
        {project_name}_conn = psycopg2.connect(
            host=pg_host,
            port=pg_port,
            database={project_name}_db,
            user={project_name}_user,
            password={project_name}_password
        )
        {project_name}_conn.set_isolation_level(ISOLATION_LEVEL_AUTOCOMMIT)

        repo_root = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
        schema_path = os.path.join(repo_root, 'database', 'schema.sql')
        if not os.path.exists(schema_path):
            print(f"Error: schema file not found at {schema_path}")
            sys.exit(1)

        with open(schema_path, 'r', encoding='utf-8') as f:
            schema_sql = f.read()

        with {project_name}_conn.cursor() as cursor:
            print("Ensuring required extensions...")
            cursor.execute("CREATE EXTENSION IF NOT EXISTS pgcrypto")
            print(f"Applying schema from {schema_path}...")
            cursor.execute(schema_sql)
            print("✓ Schema applied")

        {project_name}_conn.close()
        print("✓ Database setup complete")
        print(f"Database: {{project_name}_db}")
        print(f"User: {{project_name}_user}")
        print(f"Host: {pg_host}:{pg_port}")

    except psycopg2.Error as e:
        print(f"Error: {e}")
        sys.exit(1)
    except Exception as e:
        print(f"Unexpected error: {e}")
        sys.exit(1)


if __name__ == "__main__":
    main()

CRITICAL: Replace ALL instances of:

• {PROJECT_NAME} → uppercase project name (e.g., ARCANA, MYAPP)
• {project_name} → lowercase project name (e.g., arcana, myapp)

Step 5: Create Documentation

Add a section to the project's README.md (or create SETUP.md) documenting:

Command Line Arguments

Required:

• --pg-password - PostgreSQL superuser password

Optional:

• --pg-user - PostgreSQL superuser name (default: postgres)
• --test-db - Create test database instead of main database

Environment Variables

PostgreSQL connection (optional):

• POSTGRES_HOST - PostgreSQL host (default: localhost)
• POSTGRES_PORT - PostgreSQL port (default: 5432)

Project-specific:

• {PROJECT_NAME}_PG_DB - Database name (default: {project_name})
• {PROJECT_NAME}_PG_USER - Application user (default: {project_name})
• {PROJECT_NAME}_PG_PASSWORD - Application user password (REQUIRED)

Setup Instructions

# Set required environment variables
export {PROJECT_NAME}_PG_PASSWORD="your_app_password"

# Run setup script (pass postgres superuser password as argument)
python dev_scripts/setup_database.py --pg-password "your_postgres_password"

# With custom superuser name
python dev_scripts/setup_database.py --pg-password "your_postgres_password" --pg-user "admin"

# For test database
python dev_scripts/setup_database.py --pg-password "your_postgres_password" --test-db

Step 6: Make Script Executable

Run:

chmod +x dev_scripts/setup_database.py

Step 7: Create Database Driver (Optional but Recommended)

If the project needs a database driver/connection manager, create one following this pattern:

File: src/{project_name}/driver/database.py

Key patterns to follow:

1. Connection Pooling: Use ThreadedConnectionPool from psycopg2

   from psycopg2.pool import ThreadedConnectionPool
   
   self.pool = ThreadedConnectionPool(
       min_conn,  # e.g., 2
       max_conn,  # e.g., 10
       host=db_host,
       database=db_name,
       user=db_user,
       password=db_passwd
   )
   

2. Context Managers: Provide context managers for connections and cursors

   @contextmanager
   def get_cursor(self, commit=True, cursor_factory=None):
       """Context manager for database cursors with automatic commit/rollback"""
       with self._get_connection() as conn:
           cursor = conn.cursor(cursor_factory=cursor_factory)
           try:
               yield cursor
               if commit:
                   conn.commit()
           except Exception:
               conn.rollback()
               raise
           finally:
               cursor.close()
   

3. Always Use RealDictCursor for Loading Data: When reading from database, use RealDictCursor

   from psycopg2.extras import RealDictCursor
   
   with self.get_cursor(commit=False, cursor_factory=RealDictCursor) as cursor:
       cursor.execute("SELECT * FROM table WHERE id = %s", (id,))
       result = cursor.fetchone()
       return Model.from_dict(dict(result))
   

4. Unix Timestamps Everywhere: Convert database timestamps to/from unix timestamps

   # When saving to DB - store as BIGINT
   created_at = int(time.time())
   
   # When loading from DB - already BIGINT, use as-is
   # In models, store as int (unix timestamp)
   # Only convert to datetime for display/formatting purposes
   

5. Proper Cleanup: Ensure pool is closed on destruction

   def close(self):
       if self.pool and not self.pool.closed:
           self.pool.closeall()
   
   def __del__(self):
       if hasattr(self, 'pool'):
           self.close()
   

Example Driver Structure:

class {ProjectName}DB:
    def __init__(self, db_host, db_name, db_user, db_passwd, min_conn=2, max_conn=10):
        self.pool = ThreadedConnectionPool(...)

    @contextmanager
    def get_cursor(self, commit=True, cursor_factory=None):
        # Context manager for cursors
        pass

    def load_item_by_id(self, item_id: str) -> Item:
        with self.get_cursor(commit=False, cursor_factory=RealDictCursor) as cursor:
            cursor.execute("SELECT * FROM items WHERE id = %s", (item_id,))
            result = cursor.fetchone()
            if not result:
                raise Exception(f"Item {item_id} not found")
            return Item.from_dict(dict(result))

    def save_item(self, item: Item) -> str:
        with self.get_cursor() as cursor:
            cursor.execute(
                "INSERT INTO items (name, created_at) VALUES (%s, %s) RETURNING id",
                (item.name, int(time.time()))
            )
            return str(cursor.fetchone()[0])

Design Principles

This pattern follows these principles:

Database Schema:

1. Separation of concerns - SQL in .sql files, setup logic in Python
2. Idempotency - Safe to run multiple times
3. Test database support - Easy to create isolated test environments
4. Unix timestamps - Always use BIGINT for dates/times (not TIMESTAMP types)
5. UUIDs for keys - Better for distributed systems
6. Environment-based config - No hardcoded credentials

Database Driver (if applicable):

1. Connection pooling - Use ThreadedConnectionPool for efficient connection reuse
2. Context managers - Automatic commit/rollback and resource cleanup
3. RealDictCursor for reads - Always use RealDictCursor when loading data for easy dict conversion
4. Unix timestamps - Store as BIGINT, convert only for display
5. Proper cleanup - Close pool on destruction

Example Usage in Claude Code

User: "Set up postgres database for my project" Claude: "What is your project name?" User: "trading-bot" Claude:

1. Creates database/ and dev_scripts/ directories
2. Creates database/schema.sql with skeleton
3. Creates dev_scripts/setup_database.py with:
   • TRADING_BOT_PG_PASSWORD
   • trading_bot database and user
4. Documents environment variables needed
5. Makes script executable