Iterating through array of models with complex relations in Ruby

Question

So I have done this kind of thing countless times in the past, but I can't seem to wrap my head around why this isn't working this time. I am fairly new to RoR and I was using some new relations in my model, that is the only reason I can think of so far.

User model has the following relations

  has_one :profile

  has_many :follower_relationships, class_name: "Follow", foreign_key: "following_id"
  has_many :followers, through: :follower_relationships, source: :follower

  has_many :following_relationships, class_name: "Follow", foreign_key: "user_id"
  has_many :following, through: :following_relationships, source: :following

I am trying to list the followers of any one particular user, but the names are stored in the user profile. I have tried doing this:

In the conroller: 

def followers
  @followers = User.find_by(id: params[:user_id]).followers
end

In the html.erb file:

<% for i in [email protected] %>
   <%= @followers[i].profile.first_name %>
<% end %>

So, I initially tried for.each before trying a ordinary for loop. But it always returns

ActionView::Template::Error (undefined method `first_name' for nil:NilClass):
    2:
    3:
    4: <% for i in [email protected] %>
    5: <%= @followers[i].profile.first_name %>
    6: <% end %>

However, putting <%= @followers.first.profile.first_name %> returns the first_name of the first follower.

Why does calling the first item in the array work when I am trying this but not when I am trying to iterate over the entire array?

Very rarely would a for loop be used in ruby instead this would be <% @followers.each do |follower| %> then you would just use the piped local variable follower inside the block. Also just because @followers.first has a profile does not mean that @followers.forty_two does — engineersmnky
– engineersmnky, Commented May 27, 2020 at 20:37
I seeded the database... so all of them have profiles. Also, I did use <% @followers.each do |follower| %> as I said in the question but it returned the same thing. — Chandler White
– Chandler White, Commented May 27, 2020 at 20:43
Then one of the followers does not have a profile. Try this and see User.find_by(id: params[:user_id]).followers.left_joins(:profile).where(profiles: {id: nil}) — engineersmnky
– engineersmnky, Commented May 27, 2020 at 20:47
It didn't return anything #<ActiveRecord::AssociationRelation []>. I seeded every profile and user in the database together, so all users present have profiles. — Chandler White
– Chandler White, Commented May 27, 2020 at 21:02
There is no reason for that error in that location except that profile returns nil. Try changing to profile&.first_name and see where the empty result is. — engineersmnky
– engineersmnky, Commented May 27, 2020 at 21:09

Beulah Akindele · Accepted Answer · 2020-05-27 21:39:40Z

2

Well... if you use a for-loop. You should probably go from 0..(@followers.length - 1) if not, it'll return a (undefined methodfirst_name' for nil:NilClass)` error like you are seeing.

<% for i in 0..(@followers.length-1) %>
   <%= @followers[i].profile.first_name %>
<% end %>

or better yet, use the for.each and send the error. if there is any.

<% @followers.each do |f| %>
  <%= f.profile.first_name %>
<% end %>

answered May 27, 2020 at 21:39

Beulah Akindele

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2 Comments

Chandler White Over a year ago

I must have made a typo or something when I was using the .each, cause it is working now. @engineersmnky

tblev Over a year ago

@ChandlerWhite the .where query method always returns a relation (an array). the .each loops through each index of it.

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