Rails + Apartment + PostGIS + activerecord-postgis-adapter

apartment.rb

Apartment.configure do |config|
  config.persistent_schemas = %w{ shared_extensions }
end

database.yml

defaults: &defaults
  adapter: postgis
  postgis_extension: true
  schema_search_path: "public,shared_extensions"
  encoding: unicode
  host: 127.0.0.1
  pool: 5
  timeout: 5000

development:
  <<: *defaults
  database: development
  username:
  password:

error

CREATE TABLE "sampling_points" ("id" serial primary key, "localisation_description" text, "notes" text, "created_at" timestamp, "updated_at" timestamp, "waterbody_id" integer, "entity_id" integer, "name" character varying, "sampling_point_justification_id" integer, "slug" character varying NOT NULL, "coordinates" geometry(POINT,0))
ActiveRecord::StatementInvalid: PG::UndefinedObject: ERROR:  type "geometry" does not exist
LINE 1: ... "slug" character varying NOT NULL, "coordinates" geometry(P...
                                                             ^
: CREATE TABLE "sampling_points" ("id" serial primary key, "localisation_description" text, "notes" text, "created_at" timestamp, "updated_at" timestamp, "waterbody_id" integer, "entity_id" integer, "name" character varying, "sampling_point_justification_id" integer, "slug" character varying NOT NULL, "coordinates" geometry(POINT,0))
from /Users/pdionne/.rbenv/versions/2.2.0/lib/ruby/gems/2.2.0/gems/activerecord-4.2.0/lib/active_record/connection_adapters/postgresql/database_statements.rb:155:in `async_exec'

extensions.rake

namespace :db do
  desc 'Creates shared_extensions Schema and enables postgis extension'
  task :extensions => :environment  do
    # Create shared_extensions schema
    ActiveRecord::Base.connection.execute 'CREATE SCHEMA IF NOT EXISTS shared_extensions;'
    # Enable PostGIS
    ActiveRecord::Base.connection.execute 'CREATE EXTENSION IF NOT EXISTS postgis SCHEMA shared_extensions;'
  end
end

Rake::Task["db:create"].enhance do
  Rake::Task["db:extensions"].invoke
end

Rake::Task["db:test:purge"].enhance do
  Rake::Task["db:extensions"].invoke
end

gistfile1.txt

SELECT PostGIS_full_version();
OTICE:  Function postgis_topology_scripts_installed() not found. Is topology support enabled and topology.sql installed?
                                                                         postgis_full_version
----------------------------------------------------------------------------------------------------------------------------------------------------------------------
 POSTGIS="2.1.5 r13152" GEOS="3.4.2-CAPI-1.8.2 r3921" PROJ="Rel. 4.8.0, 6 March 2012" GDAL="GDAL 1.11.1, released 2014/09/24" LIBXML="2.9.1" LIBJSON="UNKNOWN" RASTER
(1 row)

migration.rb

class UpdateSamplingPointsGeo < ActiveRecord::Migration
  def change
    add_column(:sampling_points, :coordinates, :st_point, has_z: true)

    add_index :sampling_points, :coordinates, using: :gist
  end
end

schema.rb

AtiveRecord::Schema.define(version: 20150228171547) do

  # These are extensions that must be enabled in order to support this database
  enable_extension "plpgsql"
  enable_extension "postgis"
  
  create_table "sampling_points", force: :cascade do |t|
    t.geometry "coordinates",                     limit: {:srid=>0, :type=>"point"}
  end
end