Selecting points from intersecting an arbitrary (non-database) polygon with PostGIS

Question

Determining a polygon as follows, and the points to check against, in ruby

@poly = GEOFACTORY.polygon(@line_string1)
@locations = Location.all
@valid_locations = Location.order("id").where("st_intersects(ST_GeomFromText(@poly), @locations.lonlat)").all

@poly returns POLYGON ((9.0395777869 45.6141806128, 9.0395777869 45.3141806128, 9.3395777869 45.3141806128, 9.3395777869 45.6141806128, 9.0395777869 45.6141806128)) and Location.lonlat is defined with :srid => 3785. Similar queries that check against database column data run properly, however this query states

PG::UndefinedColumn: ERROR:  column "poly" does not exist

Is it possible to query postGIS with arbitrary data? If so, where is this query off track?

Answer 1

You're not interpolating the Ruby variables into the string you pass to Postgres. In other words, the WHERE query doesn't know what "@poly" means, because it doesn't have access to your running Ruby environment.

Either:

1. Interpolate the variables into the string, e.g. #{@poly}, or
2. Use placeholders

How exactly you do this will depend on the syntax of the ORM you're using, but you haven't specified what it is (ActiveRecord?). It may be more of a general Ruby question than a GIS-specific one.