Question

Let’s say we have 3 users [User name="A"], [User name="B"], [User name="C"]

Is there a difference between (to check presence):

if User.where(name: "A").first

and

User.all.map(&:name).include? "A"

Thank you.

Answer 1

Using where only retrieves users who match the name, via SQL.

Mapping loads all the users, builds an array of their names, and checks for ‘A’.

For small numbers of users the difference in performance will be negligible, but both memory and time will be substantially impacted after a certain point, and where will be much better. Doing the work in the DB will be a better option than naively retrieving all data and doing it in Ruby.