Appendix D. Glossary

Speaking in Rails

Understanding is nothing else than conception caused by speech.

Thomas Hobbes

Rails, like many communities, has developed its own language. You need to know a lot of that language to understand what other people are saying, even when those people are trying to be helpful. This glossary gives you a quick guide to some common terms used in Rails that aren’t obvious to outsiders and provides the extra Rails meanings for words used elsewhere that have acquired additional meaning in Rails. Hopefully this will make it easier for you to understand Rails documentation and conversation, but of course, new terms will emerge over time:


Atomicity, Consistency, Isolation, Durability. A set of principles, usually implemented with relational databases and transactions, that are intended to ensure data reliability. Rails is not designed with ACID as a priority, though transactions are available as a plug-in. (In a different meaning, there are also a variety of “Acid” tests for CSS implementation conformance.)


Introduced in Rails 5, ActionCable extends Rails functionality with real-time message passing with WebSockets.


The part of the Rails library that directly interacts with incoming HTTP requests, including routing, parameter passing, session management, and deciding how to render a response. Controller objects are the main way in which Rails developers interact with ActionController.


The part of ...

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