Mapped array to relation

Question

I have the following model associations:

A concert has_one location. Location is a polymorphic association (concerts are not the only locatables). The location is geocoded through its address attribute by the geocoder gem.

The goal is to find a concert near a certain city that will take place in the future. While the geocoder gem provides the .near(address_string) method to find a record by an address, I can only apply that method to the location class, not to the concert class.

I have come up with the following workaround:

Location.near("Berlin").where(locatable_type: 'Concert').map(&:locatable)

Let me break this down:

Location.near("Berlin")
# ==> returns locations of any kind near Berlin

.where(locatable_type: 'Concert')
# ==> returns concert locations near Berlin

.map(&:locatable)
# ==> returns an array of concerts near Berlin

The problem is that this returns an array of concerts, but I would prefer a relation so that I can use my upcoming concert scope to find only concerts that take place in the future.

Any ideas on how to do that?

Marek Lipka · Accepted Answer · 2013-10-15T10:54:04.350

1

You can have ActiveRecord::Relation doing this:

locatable_ids = Location.near('Berlin').where(locatable_type: 'Concert').map(&:locatable_id)
@concerts = Concert.where(id: locatable_ids).upcoming

edited Oct 15 '13 at 10:54

answered Oct 15 '13 at 10:44

Marek Lipka

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@SergioTulentsev why doesn't it? – Marek Lipka Oct 15 '13 at 10:47
If I understand correctly, the OP wants something different. One query, not two. – Sergio Tulentsev Oct 15 '13 at 10:50
@SergioTulentsev I'm sorry, I can't find this requirement in question. Could you show me appropriate fragment? – Marek Lipka Oct 15 '13 at 10:53
Marek: that's what I inferred. Else why would he want to get a relation? – Sergio Tulentsev Oct 15 '13 at 10:55
@SergioTulentsev "The problem is that this returns an array of concerts, but I would prefer a relation so that I can use my upcoming concert scope to find only concerts that take place in the future." – Marek Lipka Oct 15 '13 at 10:56
Yes, a relation instead of an array. But you still return array from that query. – Sergio Tulentsev Oct 15 '13 at 10:56
@SergioTulentsev - yes, from that query. But he has relation of `Concert` objects, on which he can call `upcoming` scope, which, if I understood correctly, solves at least one of his problems. – Marek Lipka Oct 15 '13 at 10:59
Marek: anyway, I don't know how to achieve that in single query, so your answer is the best so far. :) – Sergio Tulentsev Oct 15 '13 at 11:00
@SergioTulentsev I think it's impossible (or at least very, veeeeery difficult) to achieve this in single query without changing DB schema. Even the `includes` scope produces two queries. – Marek Lipka Oct 15 '13 at 11:02
This is elegant enough ;-) Thanks a lot! – Dennis Hackethal Oct 15 '13 at 11:37
I put this in another scope: `scope :near, ->(address, radius = 50) { where(id: Location.near(address, radius).where(locatable_type: 'Concert').map(&:locatable_id)).upcoming }` - so now I can just say `Concert.near("Berlin", 50)` and it works :) – Dennis Hackethal Oct 15 '13 at 11:45

Mapped array to relation

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