Inventory Management System Design Using PostgreSQL

Why Relational Databases for Inventory

Inventory systems require strict transactional consistency (ACID properties). Unlike document-based datastores which can suffer from data duplication and eventual consistency lag, PostgreSQL ensures every transaction is fully isolated and atomic.

Creating the Inventory Schema

We treat inventory as a double-entry ledger. Instead of just updating a 'current_stock' integer, we append a transaction record. The current stock is a materialized view or sum of all transactions.

CREATE TABLE inventory_ledgers (
  id SERIAL PRIMARY KEY,
  product_id INT REFERENCES products(id),
  quantity_change INT NOT NULL,
  transaction_type VARCHAR(50) NOT NULL,
  reference_id VARCHAR(100),
  created_at TIMESTAMP DEFAULT CURRENT_TIMESTAMP
);

Utilizing Trigger Hooks

To optimize read speeds, we use PostgreSQL triggers to update a cached 'stock_summary' table every time a new ledger entry is inserted. This gives us the auditability of an append-only ledger with the read-performance of a single row lookup.

CREATE OR REPLACE FUNCTION update_stock_summary()
RETURNS TRIGGER AS $$
BEGIN
  INSERT INTO stock_summary (product_id, total_stock)
  VALUES (NEW.product_id, NEW.quantity_change)
  ON CONFLICT (product_id) DO UPDATE 
  SET total_stock = stock_summary.total_stock + NEW.quantity_change;
  RETURN NEW;
END;
$$ LANGUAGE plpgsql;