🚀 What Happens When Your API Receives the Same Request Twice?

Imagine a customer clicks “Pay Now” twice because the page freezes.

Or a payment gateway retries a request because it never received your response.

💥 Without proper protection, your application might charge the customer twice!

This is where Idempotency becomes essential.

🔍 What Is Idempotency?

Idempotency means that performing the same operation multiple times produces the same result as performing it once.

For example, if a client retries a payment request, the system should return the original result instead of creating another payment.

🛠️ How Do We Implement It in Ruby on Rails?

A common approach is using an Idempotency-Key .

The client sends a unique key with the request:

POST /api/v1/payments Idempotency-Key: order-123-payment

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Rails can use that key to identify duplicate requests.

Step 1: Add a database constraint

add_index :payments , :idempotency_key , unique: true

Enter…