July 15, 2014 by Mike Clark
In our Rails Level I course we look at how to define custom queries by writing class methods in models. For example, to find all events that occurred in the past (versus upcoming events), we write a
past method in the
Event model and then query past events using
We build on that foundation in our Rails Level II course by learning how to write custom queries using the declarative style offered by the
scope method. A scope simply names a chunk of query code, and behind the scenes it dynamically defines a class method that encapsulates the query code.
One of the keys to writing a scope is to make the query code a callable Ruby object (also called a
Proc object). It's at this point that many folks are first exposed to a Ruby
lambda, or the more cryptic
-> shortcut. As a quick introduction to how lambdas work, check out this 3-minute excerpt from the Scopes module in our Rails Level II course where we convert the
past class method to a scope:
If you found that helpful, go ahead and watch the entire Scopes module, as well as other free modules in the Rails Level II course. You can also check out the course introduction video for an overview of the application features we build in this course. Or jump right in and purchase the entire course (with downloadable HD videos!). Our course is based on Rails 4, so you'll learn and apply the most up-to-date techniques!
— Jonathan Mundy