use Ransack to sort collections

[seanlinsley]

This is a continuation of where @vjt left off in #1994

Added functionality:

• you can sort by multiple columns

Problems:

• sorting on a virtual column doesn't work
• when sorting on multiple columns, how do you tell which column (on an
  index table) is currently being sorted?

[seanlinsley]

Maybe the better option would be to always use the foo_and_bar_desc style on the client side, but to parse that back into the array form so Ransack can understand it. That would have the added benefit of giving us a valid string for the CSS class to show which column is being sorted.

[seanlinsley]

As I said over on #2844 (comment), I don't think this is the right approach because Ransack can't handle everything that a developer would want to do.

So the question becomes: how can we add the ability to sort by multiple columns (e.g. first & last name) to our current sorting code?

[hirokihokari]

@seanlinsley Seems like this got all removed on master now?

[senid231]

@seanlinsley what if we just extend AA with some sort of custom sorting option
something like:

ActiveAdmin.register Post do
  custom_sort full_name: ->(records, direction) { records.order([{last_name: direction, first_name: :asc}]) },
                       comments_count: :order_by_comments_count 
                       # shortcut for ->(records, direction) { records.order_by_comments_count(direction) }

  index do
    column :id # sorted by posts.id asc/desc, query param id_asc/id_desc
    column :full_name # sorted by lambda provided above, query param full_name_asc/full_name_desc
    column :reversed_name, sortable: :full_name do |r| # sorted same as :full_name
      r.full_name.reverse
    end
    column :comments, :comments_tag, sortable: :comments_count 
    # sorted by `order_by_comments_count` scope or class method, 
    # query param comments_count_asc/comments_count_desc
  end
end