Revert "Revert "Add readonly support for relations.""

This reverts commit f2c0725d79.

activerecord/lib/active_record/base.rb

@@ -1722,7 +1722,7 @@ module ActiveRecord #:nodoc:
 
         def construct_finder_arel(options = {}, scope = scope(:find))
           # TODO add lock to Arel
-          arel_table(options[:from]).
+          relation = arel_table(options[:from]).
             joins(construct_join(options[:joins], scope)).
             conditions(construct_conditions(options[:conditions], scope)).
             select(options[:select] || (scope && scope[:select]) || default_select(options[:joins] || (scope && scope[:joins]))).
@@ -1730,6 +1730,11 @@ module ActiveRecord #:nodoc:
             order(construct_order(options[:order], scope)).
             limit(construct_limit(options[:limit], scope)).
             offset(construct_offset(options[:offset], scope))
+
+          relation = relation.readonly if options[:readonly]
+
+          relation
+
         end
 
         def construct_finder_sql(options, scope = scope(:find))

activerecord/lib/active_record/relation.rb

@@ -5,10 +5,20 @@ module ActiveRecord
 
     def initialize(klass, relation)
       @klass, @relation = klass, relation
+      @readonly = false
+    end
+
+    def readonly
+      @readonly = true
+      self
     end
 
     def to_a
-      @klass.find_by_sql(@relation.to_sql)
+      records = @klass.find_by_sql(@relation.to_sql)
+
+      records.each { |record| record.readonly! } if @readonly
+
+      records
     end
 
     def each(&block)

activerecord/test/cases/relations_test.rb

@@ -79,5 +79,11 @@ class RelationTest < ActiveRecord::TestCase
       assert relation.respond_to?(method)
     end
   end
+
+  def test_find_with_readonly_option
+    Developer.all.each { |d| assert !d.readonly? }
+    Developer.all.readonly.each { |d| assert d.readonly? }
+    Developer.all(:readonly => true).each { |d| assert d.readonly? }
+  end
 end