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More helpful error message when instantiating an abstract class

Calling a literal raises NoMethodError,
since it ends up calling Class.abstract_class? which does not exist.
Similarly, instantiating an actual abstract class hits the database,
when conventionally it should immediately throw NotImplementedError.

ActiveRecord::Base can't be made abstract without breaking many,
many things, so check for it separately.
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commit 53f18f2c5475809f7f6c5576aba89d6340a57c06 1 parent 48c21e3
@HonoreDB HonoreDB authored
4 activerecord/
@@ -1,5 +1,9 @@
## Rails 4.0.0 (unreleased) ##
+* Throw `NotImplementedError` when trying to instantiate Base or an abstract class.
+ *Aaron Weiner*
* Postgresql timestamp with time zone (timestamptz) datatype now returns a
ActiveSupport::TimeWithZone instance instead of a string
3  activerecord/lib/active_record/inheritance.rb
@@ -15,6 +15,9 @@ module ClassMethods
# and if the inheritance column is attr accessible, it initializes an
# instance of the given subclass instead of the base class
def new(*args, &block)
+ if abstract_class? || self == Base
+ raise NotImplementedError, "#{self} is an abstract class and can not be instantiated."
+ end
if (attrs = args.first).is_a?(Hash)
if subclass = subclass_from_attrs(attrs)
return*args, &block)
14 activerecord/test/cases/base_test.rb
@@ -307,6 +307,20 @@ def test_initialize_with_invalid_attribute
assert_equal("last_read", ex.errors[0].attribute)
+ def test_initialize_abstract_class
+ e = assert_raises(NotImplementedError) do
+ end
+ assert_equal("FirstAbstractClass is an abstract class and can not be instantiated.", e.message)
+ end
+ def test_initialize_base
+ e = assert_raises(NotImplementedError) do
+ end
+ assert_equal("ActiveRecord::Base is an abstract class and can not be instantiated.", e.message)
+ end
def test_create_after_initialize_without_block
cb = CustomBulb.create(:name => 'Dude')
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