What's the difference between “includes” and “joins” in ActiveRecord query?

Question

What\'s the difference between \"includes\" and \"joins\" in ActiveRecord query? Can anyone explain to me with the following two associated

Answer 1

:joins returns read-only objects, :includes does not

:joins uses inner join, :includes uses outer join.

the main reason of :includes is eager loading, to avoid the N+1 problem of loading in attributes of each object using a separate query.