Rails where method with any created_at - ruby-on-rails

Question

I've got a method like this:
def transfers(material, capacity, category, created_at)
transfers_range = Transfer.first.created_at..Transfer.last.created_at if created_at.nil?
Transfer.where(
sender_dispensary_id: id,
status: %i[dispatched released returned],
capacity: capacity,
material: material,
created_at: created_at.nil? ? transfers_range : Time.given_month_range(created_at)
).or(
Transfer.where(
receiver_dispensary_id: id,
status: %i[dispatched released returned],
capacity: capacity,
material_id: material,
created_at: created_at.nil? ? transfers_range : Time.given_month_range(created_at)
)
)
end
It's working, but is there a way to avoid query for transfer_range? I mean... If created_at == nil, then this function should skip created_at column, like it was not included in query

Answer 1

When created_at is nil then transfers_range basically covers all transfers and therefore the condition is pointless and I simple would query by created_at in that case.
def transfers(material, capacity, category, created_at)
transfers = Transfer
.where(status: %i[dispatched released returned], capacity: capacity, material_id: material)
.where('sender_dispensary_id = :id OR receiver_dispensary_id = :id', id: id)
transfer = transfer.where(created_at: Time.given_month_range(created_at)) if created_at
transfer
end

Answer 2

Yes, the transfers_range query can be avoided by breaking your query into multiple lines and adding a condition on created_at presence separately. You can also combine both the OR queries into a single query like this:
def transfers(material, capacity, category, created_at)
transfer_data = Transfer.where('sender_dispensary_id = ? OR receiver_dispensary_id = ?', id).where(status: %i[dispatched released returned], capacity: capacity, material_id: material)
transfer_data = transfer_data.where(created_at: Time.given_month_range(created_at)) if created_at.present?
transfer_data
end

Answer 3

You can consolidate the created_at query logic so it's in one place and you don't have to repeat it.
created_at = if created_at.nil?
Transfer.first.created_at..Transfer.last.created_at
else
Time.given_month_range(created_at)
end
You also don't need to repeat the whole where condition twice. You want the equivalent of...
where status in ('dispatched', 'released', 'returned')
and capacity = ?
and material = ?
and created_at = ?
and (
sender_dispensary_id = ?
or
receiver_dispensary_id = ?
)
You do that like so:
Transfer
.where(
status: %i[dispatched released returned],
capacity: capacity,
material: material,
created_at: created_at
)
.where(
Transfer
.where(receiver_dispensary_id: id)
.or(Transfer.where(sender_dispensary_id: id))
)
)
You can make this even more concise, and hide the details, by putting the logic into a scopes.
class Transfer < Application
scope :by_dispensary_id ->(id) {
where(receiver_dispensary_id: id)
.or(where(sender_dispensary_id: id))
}
scope :by_created_month ->(time) {
if time.nil?
where(created_at: first.created_at..last.created_at)
else
where(created_at: Time.given_month_range(time))
end
}
end
And now the query is much simpler.
Transfer
.by_dispensary_id(id)
.by_created_month(created_at)
.where(
status: %i[dispatched released returned],
capacity: capacity,
material: material
)
)