Transactions

A database transaction groups a series of changes in such a way that either the database applies all of the changes or it applies none of the changes. The classic example of the need for transactions (and one used in Active Record’s own documentation) is transferring money between two bank accounts. The basic logic is simple:

​ account1.deposit(100)
​ account2.withdraw(100)

However, we have to be careful. What happens if the deposit succeeds but for some reason the withdrawal fails (perhaps the customer is overdrawn)? We’ll have added $100 to the balance in account1 without a corresponding deduction from account2. In effect, we’ll have created $100 out of thin air.

Transactions to the rescue. A transaction is something ...

Get Agile Web Development with Rails 5, 1st Edition now with the O’Reilly learning platform.

O’Reilly members experience live online training, plus books, videos, and digital content from nearly 200 publishers.