Fix stream query for postgres, shouldn't break mysql

Gemfile

@@ -1,6 +1,7 @@
 source 'http://rubygems.org'
 
-gem 'mysql2', '0.2.6'
+#gem 'mysql2', '0.2.6'
+gem 'pg'
 gem 'rails', '3.0.3'
 gem 'foreigner', '0.9.1'
 

Gemfile.lock

@@ -226,7 +226,6 @@ GEM
     multi_json (1.0.3)
     multi_xml (0.2.2)
     multipart-post (1.1.2)
-    mysql2 (0.2.6)
     net-ldap (0.2.2)
     net-scp (1.0.4)
       net-ssh (>= 1.99.1)
@@ -283,6 +282,7 @@ GEM
       oa-openid (= 0.2.6)
     open4 (1.0.1)
     orm_adapter (0.0.5)
+    pg (0.11.0)
     polyglot (0.3.1)
     pyu-ruby-sasl (0.0.3.3)
     rack (1.2.3)
@@ -430,11 +430,11 @@ DEPENDENCIES
   linecache (= 0.43)
   mini_magick (= 3.2)
   mongrel
-  mysql2 (= 0.2.6)
   newrelic_rpm
   nokogiri
   ohai (= 0.5.8)
   omniauth (= 0.2.6)
+  pg
   rails (= 3.0.3)
   rcov
   resque (= 1.10.0)

lib/diaspora/user/querying.rb

@@ -42,11 +42,27 @@ module Diaspora
         posts_from_self = posts_from_self.select(select_clause).limit(opts[:limit]).order(order_with_table).where(Post.arel_table[order_field].lt(opts[:max_time]))
 
         all_posts = "(#{posts_from_others.to_sql}) UNION ALL (#{posts_from_self.to_sql}) ORDER BY #{opts[:order]} LIMIT #{opts[:limit]}"
-        post_ids = Post.connection.execute(all_posts).map{|r| r.first}
+
+        post_ids = Post.connection.execute(all_posts).map {|post| id_for(post) }
 
         Post.where(:id => post_ids).select('DISTINCT posts.*').limit(opts[:limit]).order(order_with_table)
       end
 
+      # Determine, cache, and execute the method call needed to extract the id from a raw result row.
+      # Returns row["id"] for PostgreSQL
+      # Returns row.first for everything else (MYSQL)
+      #
+      # @param row The row to get the id from.
+      # @return The id of the database row passed in.
+      def id_for row
+        @@id_method_for_row ||= if Post.connection.class == ActiveRecord::ConnectionAdapters::PostgreSQLAdapter
+                                  [:[], "id"]
+                                else
+                                  :first
+                                end
+        row.send(*@@id_method_for_row)
+      end
+
       def visible_photos(opts = {})
         visible_posts(opts.merge(:type => 'Photo'))
       end