Order by Nearest using PostGIS, RGeo, Spatial Adapter

I'm asking this question because the answers I've found in Order by nearest - PostGIS, GeoRuby, spatial_adapter wasn't able to provide a solution. I'm trying to create a controller method that can return the n closest records to a certain record's lonlat. The record it is querying against is from the same table. This concept isn't such a big stretch if I was doing this completely in SQL. That much is clear in the linked example and below is a specific case where I obtained a result:

condos_development=#
  SELECT id, name FROM condos
  ORDER BY ST_Distance(condos.lonlat, ST_PointFromText('POINT(-71.06 42.45)'))
condos_development-#
  LIMIT 5;

My problem is in making this work with ActiveRecord. I'm using a method that was inspired by the response by @dc10 but I'm unable to create a working query either through the RGeo methods, or direct SQL. Here's what I have so far:

def find_closest_condos(num, unit)
  result = Condo.order('ST_Distance(condos.lonlat, ST_PointFromText("#{unit.lonlat.as_text)}")')
                .limit(5)
end

The response from this attempt is as follows:

ActiveRecord::StatementInvalid: PG::SyntaxError: ERROR: syntax error at or near "LIMIT" 10:29:50 rails.1 LINE 1: ...lonlat, ST_PointFromText("#{unit.lonlat.as_text)}") LIMIT $1

Would someone be able to set me on the right track on how to put this work query together so that I can make it work in Rails?

Solution

The problem is with how active record is resolving your query to SQL, also the position of the Limit clause. If you change the query to this:

Condo.order("ST_Distance(lonlat, ST_GeomFromText('#{unit.lonlat.as_text}', 4326))")
     .limit(num)

You should find this works.