Creating an array from activerecord objects

Question

When in the rails console the following code prints to screen an array of coordinates in geojson format as I expect it to:

Bg.
  select("bg_id, ST_AsGeoJSON(the_geom) as my_geo").
  where("ST_Contains(ST_MakeEnvelope(-xxx,xxx,-xxx,xxx, 4269), bg.the_geom)").
  map(&:my_geo)

The select portion however isn't just asking for the json. What if I would also like the bg_id's in the array too?

Abe Voelker · Accepted Answer · 2013-05-03 19:03:00Z

1

What kind of inner data structure are you trying to end up with (i.e. where are you going to put the bg_ids)? E.g. if it's just a hash I think you could change

map(&:my_geo)

to

map{|b| {b.id => b.my_geo} }

answered May 3, 2013 at 19:03

Abe Voelker

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3 Comments

Nick McD. Over a year ago

Ultimately what I want is a hash with the bg_id's as the keys and the geojson objects as the values. What you provided here creates an array of hashes. I used .reduce Hash.new, :merge to make a single hash exactly as I would like it. So I guess my question is answered unless you can think of an better way. Thanks!

Nick McD. Over a year ago

Also, although this works, I'm not sure I understand why. This looks like it is calling methods called id and my_geo on each item of the array... Is that correct?

Abe Voelker Over a year ago

Ah, yeah in that case reduce is the way to go. Yes that's correct, it's calling methods. (&:my_geo) is shorthand for {|obj| obj.my_geo}

Andreyy · Accepted Answer · 2013-05-03 19:25:22Z

1

You just need to remove the map and active record objects.

results = Bg.select("bg_id, ST_AsGeoJSON(the_geom) as my_geo").
where("ST_Contains(ST_MakeEnvelope(-xxx,xxx,-xxx,xxx, 4269), bg.the_geom)")

And then:

results[0].bg_id
results[0].my_geo

Or use map if you want an array of something else. Like an array of arrays [[bg_id1,my_geo1],[bg_id2,my_geo2]...]:

results.map{|b| [b.bg_id,b.my_geo] }

answered May 3, 2013 at 19:25

Andreyy

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