Scope Order by Count with Conditions Rails - ruby-on-rails

Question

I have a model Category that has_many Pendencies. I would like to create a scope that order the categories by the amount of Pendencies that has active = true without excluding active = false.
What I have so far is:
scope :order_by_pendencies, -> { left_joins(:pendencies).group(:id).order('COUNT(pendencies.id) DESC')}
This will order it by number of pendencies, but I want to order by pendencies that has active = true.
Another try was:
scope :order_by_pendencies, -> { left_joins(:pendencies).group(:id).where('pendencies.active = ?', true).order('COUNT(pendencies.id) DESC')}
This will order by number of pendencies that has pendencies.active = true, but will exclude the pendencies.active = false.
Thank you for your help.

Answer 1

I guess you want to sort by the amount of active pendencies without ignoring categories that have no active pendencies.
That would be something like:
scope :order_by_pendencies, -> {
active_count_q = Pendency.
group(:category_id).
where(active: true).
select(:category_id, "COUNT(*) AS count")
joins("LEFT JOIN (#{active_count_q.to_sql}) AS ac ON ac.category_id = id").
order("ac.count DESC")
}
The equivalent SQL query:
SELECT *, ac.count
FROM categories
LEFT JOIN (
SELECT category_id, COUNT(*) AS count
FROM pendencies
GROUP BY category_id
WHERE active = true
) AS ac ON ac.category_id = id
ORDER BY ac.count DESC
Note that if there are no active pendencies for a category, the count will be null and will be added to the end of the list.
A similar subquery could be added to sort additionally by the total amount of pendencies...

Answer 2

C# answer as requested:
method() {
....OrderBy((category) => category.Count(pendencies.Where((pendency) => pendency.Active))
}
Or in straight SQL:
SELECT category.id, ..., ActivePendnecies
FROM (SELECT category.id, ..., count(pendency) ActivePendnecies
FROM category
LEFT JOIN pendency ON category.id = pendency.id AND pendnecy.Active = 1
GROUP BY category.id, ...) P
ORDER BY ActivePendnecies;
We have to output ActivePendnecies in SQL even if the code will throw it out because otherwise the optimizer is within its rights to throw out the ORDER BY.

Answer 3

For now I developed the following (it's working, but I believe that it's not the best way):
scope :order_by_pendencies, -> { scoped = Category.left_joins(:pendencies)
.group(:id)
.order('COUNT(pendencies.id) DESC')
.where('pendencies.active = ?', true)
all = Category.all
(scoped + all).uniq}