Styjun

I'm working on a social networking media like Facebook.
Users can create daily posts and events.

In timeline, I want to display a combined list of @post and @event. Can I build that on Rails?

How about this below in controller:

@feed = Post.all + Event.all

And I should divide each thumbnail view also.

So multiple item combined.

Adding every single Post and Event to an array on memory es really dangerous, don't do that!

I can think of 2 solutions for your problem.

1- The easiest

Add an extra model with a polymorphic association to a Post or an Event and the created_at every time you create one of them. Then you can sort and paginate that extra model at database level. This way you won't have memory problems.

You could have some helper method to preload the post and events of that result set to prevent an N+1 queries problem since you can't use includes/references on polymorphic associations.

Pros: easy to implement

Cons: adds an extra model, you need to implement the preload of information to prevent N+1 queries, if you need to add some where statement you'll have to copy the data or join the table with the others.

2- The hardest

Use a UNION query with both tables and return the necesary fields just to display them.

union_qry = "(SELECT 'Post', id, created_at, '' as title, '' as place FROM posts) UNION (SELECT 'Event', id, created_at, title, place FROM events)"

arr = ActiveRecord::Base.connection.execute("#search_qry ORDER BY created_at DESC LIMIT #per OFFSET #offset") #note the per and offset if you need pagination

That query will return a MySQL::Result that you can iterate and for each record you'll have an array like:

['Post', post_id, post_created_at, '', '']

or

['Event', event_id, event_created_at, event_title, event_place]

With those arrays you can build your list of Post+Event, if you need more data just add that to the UNION statement.

Pros: no need for an extra element, no need to repeat info, you can use where on other fields

Cons: it's far from ActiveRecord, no nice queries, no nice ActiveRecor object

Personally I prefer option 2, it's more flexible, but option 1 is easier.

Here's a very simple implementation of what you're asking for:

@feed = [*Post.all, *Event.all].sort_by(&:created_at)

Then in your view:

@feed.each do |thing|
 # thing can be a Post or an Event
end