Question

I have a relationship table for users and related users.

If I do @user.related_users I get a list of user_id that point to the users.

On my view I want to list their names with

<% current_user.related_users.each do |u| %>
<%= User.find(u).name %>
<% end %>

I worry that it might overload the DB too much, since it fetches every related_user from the DB every time someone access that view.

Is there a better way of doing this? or that is the way and there’s nothing I can do about it?

Answer 1

That’s what eager loading is for. Ideally, in your model, related_users should be an association:

has_many :related_users # add conditions to find the related users if necessary

Then in your controller, fetch the @user like this:

@user = User.includes(:related_users)

That will perform only 1 query for all related users, instead of one query for each related user (a so-called 1+N problem).

Or, if you don’t want to rewrite your model code, simply load all related users into a variable in your controller:

@related_user = User.where(id: current_user.related_users)

and iterate over that in your view. This will fetch all related users with a single query with a WHERE id IN (...) clause.