Rails 4：通过关联循环

Question

I am having some trouble while looping some association:

#=> member.rb
has_one :academic

#=> academic.rb
belongs_to :member

So far so good. However, when I loop through the association, I get:

undefined method 'each' for #<Academic:0x007fc98b2b7210>

Here's my view (show):

<% if !@member.academic.nil? %>
 <% fields_academic = [:major, :second_major, :minor, :second_minor] %>

  <h1>Academics</h1>

  <% @member.academic.each do |academic| %>
 <%= render 'database/shared/display', model_obj: academic, data: academic, fields: fields_academic %>
  <% end %>
<% end %>

The code is stuck at the each method.

@member is defined as = Member.find(params[:id])

Any help will be gladly appreciated. Thank you in advance!

Answer 1

According to your code there are no multiple instances of academic related to the given member (it's defined using has_one relation).

The answer is: you cannot loop them.

The correct code for your view should be:

<% if @member.academic.present? %>
 <% fields_academic = [:major, :second_major, :minor, :second_minor] %>
  <h1>Academics</h1>
  <%= render 'database/shared/display', model_obj: @memeber.academic, data: academic, fields: fields_academic %>
 <% end %>
<% end %>

If your intention was to have many academics for a memeber, then use has_many instead.

class Member
  has_many :academics
end

Answer 2

each should be used on a collection of records ( I mean which results in a multiple records). Currently @member.academic will return a single record as it is a has_one relation between member and academic , so you can't loop with that. May be you should change your association to has_many :academics and loop it like <% @member.academics.each do |academic| %> <% @member.academics.each do |academic| %>

Answer 3

Method :each iterates over the block according to how this Enumerable was constructed. If no block is given, returns self. Enumerable is a mixin that provides to collections some useful methods. In your example academic is a not Enumerable, but single object. You should use has_many association.