Question

I have items (documents) in Ruby on Rails that have zero or many attributes. The document attribute has a type (“Author”, “Publisher” etc). Each document can have multiple attributes of the same type.

These are currently just pulled out the the db and listed as follows:

<% @document.attribute_documents.each do |doc_attr| %>
  <b><%= doc_attr.attribute_type.try(:name) %>: </b>
  <%= "  #{doc_attr.value}" %>
  <%= ", #{doc_attr.attribute_location}" unless doc_attr.attribute_location.blank? %>
  <%= ", #{doc_attr.attribute_year}" unless doc_attr.attribute_year.blank? %><br />
<% end %>

Which gives a result like this, less than satifactory:

Publisher: William Cavell, Holborn, London
Printer: William Cavell, Holborn, London
Seller: J Barber, Newcastle
Seller: C Etherington, York
Seller: Fletcher and Hodson, Cambridge
Seller: Wilson, Dublin

What I am looking for is this:

Publisher: William Cavell, Holborn, London
Printer: William Cavell, Holborn, London
Sellers: J Barber, Newcastle, C Etherington, York, Fletcher and Hodson, Cambridge, Wilson, Dublin

So I need to group on attribute type, and then loop through the values depending on the type. Is there a simple way to doing this in RoR? Is my approach all wrong?

Answer 1

Use rails’ group_by method:

<% @document.attribute_documents.group_by { |d| d.attribute_type.try(:name) }.each_pair do |type, doc_attrs|
  <b><%= type %>: </b>
  <% doc_attrs.each do |doc_attr| %>
    <%= "  #{doc_attr.value}" %>
    <%= ", #{doc_attr.attribute_location}" unless doc_attr.attribute_location.blank? %>
    <%= ", #{doc_attr.attribute_year}" unless doc_attr.attribute_year.blank? %><br />
  <% end %>
<% end %>

Haven’t tested this, but I think it should work.

UPDATE: This will leave out commas between entries in each line. I’ll come back to it later, basically you need to use map and then join on the doc_attrs array.

UPDATE(2):

Here’s the expression that I was looking for, to go in the doc_attrs.each loop:

doc_attrs.map do |doc_attr|
  [:value, :attribute_location, :attribute_year].map do |attr|
    doc_attr.send(attr)
  end.delete_if(&:blank?).join(", ")
end.join(", ")

I don’t use erb anymore so not quite sure how to translate it, but probably better anyway to create a helper function and build it up that way.