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Rails tip: use #presence to get params value, or default to a preset value

by Axel Kee 21 August 2021

Here’s a method I encountered recently at my work and I found it might be useful to you as well.

There might be some attribute which you want to set to a default parameter if the user didn’t supply any, eg:

# if the parameters is nil or blank, we will default to french fries
sides = params[:sides].present? ? params[:sides] : "french fries"

This one liner looks concise, but we can make it even shorter like this :

sides = params[:sides].presence || "french fries"

The presence method will return nil if the string is a blank string / empty array or nil , then the || (double pipe) will use the value on the right side (“french fries”).

# => nil

If the string is not blank, .presence will return the string itself.

When params[:sides] == “” :

sides = params[:sides].presence || "french fries"
# => "french fries"

When params[:sides] == “corn” ,

sides = params[:sides].presence || "french fries"
# => "corn"

Documentation :