size doesn’t hit the database if things are loaded?. But when are things loaded? — let’s look.
Understanding loaded?
First, an example:
class PostsController < ApplicationController
def index
@posts = Post.all
@users = User.all
render json: @posts
end
end
@users doesn’t get queried because we don’t do anything with it.
In more depth:
class PostsController < ApplicationController
def index
@posts = Post.all
puts @posts.loaded? # false
@posts = @posts.where(hidden: false)
puts @posts.loaded? # false
some_inline_serialized_thing = @posts.map { |post| { id: post.id, title: post.title }}
puts @posts.loaded? # true
end
end
count vs size
In this case, if we call count, we tell the object to send a count query.
A simplified version of size looks like this under the hood:
def size
if loaded?
to_a.size
else
count
end
end
Whereas count will always hit the database.