Enterprise Rails

Understanding All the Pieces

This section gives a brief introduction to each piece of the enterprise system.

Persistence Layer

The persistence layer is where you store your business’s data. As the name implies, data here sticks around for a long time; it persists until you explicitly change or remove it. Most frequently, the persistence layer is a Relational Database Management System (RDBMS).

Because protecting your data is critical, the persistence layer should provide certain guarantees, collectively referred to as ACID: atomicity, consistency, isolation, and durability. Each of these properties plays a different role in maintaining the integrity of your data:

Atomicity

The ability to group a number of operations together into a single transaction: either they all succeed, or they all fail. The RDBMS should ensure that a failure midway through the transaction does not leave the data in an intermediary, invalid state. For example, a bank account transfer requires debiting funds from one account and crediting funds in another. If one of the operations fails, the other should be rolled back as well; otherwise, one account may be debited without making the corresponding credit in the other account.

Consider the following instructions:

account1.debit(50)
# power failure happens here
account2.credit(50)

If the database fails between the two statements, where we have a comment to the same effect, the user of the ATM system will likely see an error on-screen and expect no transaction took place. ...