Question

Greetings
I have 3 db tables:

Types
id
name

Sources
id
name
type_id

Operations
id
source_id
comment
…

and models for each:

class Type < ActiveRecord::Base
  has_many :sources, :dependent => :destroy
end

class Source < ActiveRecord::Base
  belongs_to :type
  has_many :operations, :dependent => :destroy
end

class Operation < ActiveRecord::Base
  belongs_to :source
  default_scope :order => 'created_at DESC'
end

In Operation#index controller i have code for getting data (generated by scaffolding)

@operations = Operation.all

And piece of view operations/index.html.erb also generated by scaffolding

<% @operations.each do |operation| %>
  <tr>
    <td><%= operation.source_id %></td>
    <td><%= operation.comment %></td>
  </tr>
<% end %>

Now I want to use source.name instead of *operation.source_id*

I tried to do:

-replace operation.source_id to operation.sources.name # doesn’t work

-tried to using :joins, and can’t get Sources table fields

irb(main):057:0> Operation.first( :joins => :source )
=> #<Operation id: 2088, source_id: 1, summ: 10.0, comment: "", created_at: "2011-01-01 07:39:45", updated_at: nil>

or

irb(main):063:0> Operation.first( :joins => 'INNER JOIN sources ON operations.source_id = sources.id' )
=> #<Operation id: 2088, source_id: 1, summ: 10.0, comment: "", created_at: "2011-01-01 07:39:45", updated_at: nil>

How I must properly use :joins for get additional field?
Or there is another approach to get combined tables data.

And why in the operations/show.html.erb i can use <%= @operation.source.name %> and successfully get source.name, but in the *operations/index.html.er*b can’t

Answer 1

<% @operations.each do |operation| %>
  <tr>
    <td><%= operation.source.name %></td>
    <td><%= operation.comment %></td>
  </tr>
<% end %>

I’d also recommend changing your #index method to use an includes statement to avoid an N+1 situation (i.e. running a separate database query for each individual operation’s source).

@operations = Operation.includes(:source).all