Question

I am building a prototype of a education application using Rails 3, omniauth and the facebook graph api. So when a User log in to my application he uses his facebook account, I grab all his education history and his friends education_history.

I would like to group every User friends education likes this:

I have tried something like this:

<ul class="friends-list">
<%= current_user.friends.group_by(&:highschool_name) do |highschool_name| 
 p "<li>#{highschool_name}</li>"
 end
 %>
</ul>

And I get a syntax error.

The User tabel look like this:

[id, name, image, location, highschool_name, highschool_year, college_name, college_year, graduteschool_name, graduate_year ]

And the Friend tabel looks like this:

[id, uid, name, image, higschool_name, college_name, graduateschool_name, user_id]

How do solve my problem using active record, without loops because their are not effectivity.. right?

Answer 1

You can’t use p or puts in ERB files. Think of ERB files as one big string concatenated together. Like "string 1" + "string 2" + "string 3".

That’s all ERB does – it just pastes strings together into one big string. You can’t call puts inside this concatenation operation. So everything in the ERB file needs to be a string. The output from a puts call just ‘goes up in smoke’ since a puts call does not return a string, it writes to stdout instead.

Next we look at group_by: it returns a Hash:

---------------------------------------------------- Enumerable#group_by
     enum.group_by {| obj | block }  => a_hash
------------------------------------------------------------------------
     Returns a hash, which keys are evaluated result from the block,
     and values are arrays of elements in enum corresponding to the key.

        (1..6).group_by {|i| i%3}   #=> {0=>[3, 6], 1=>[1, 4], 2=>[2, 5]}

So putting everything together we could do something like this:

<% current_user.friends.group_by(&:highschool_name).each do |hsname, friends| %>
   <% next if hsname.blank? %>
   <li><%= hsname %></li> 
   <% friends.each do |friend| %>
     <%= image_tag(friend.img_url) %> # <- Or wherever you get the img url from 
   <% end %>
<% end %>