Added ActiveRecord::Base.each and ActiveRecord::Base.find_in_batches for batch processing [DHH/Jamis Buck]

Signed-off-by: NMichael Koziarski <michael@koziarski.com>
[#1865 state:committed]

Signed-off-by: NDavid Heinemeier Hansson <david@loudthinking.com>

Signed-Off-By: NMichael Koziarski <michael@koziarski.com>

[#1202 state:committed]

Signed-off-by: NPratik Naik <pratiknaik@gmail.com>

Rewrite ActiveRecord::Base#destroy_all docs to remove incorrect info, mention return value, and improve clarity

(The incorrect information is "at least 2*N database queries" -- it's N+1 at best.)

Rewrite ActiveRecord::Base#delete docs to remove false information about callbacks, mention return value, and improve clarity

Introduce dynamic scopes for ActiveRecord: you can now use class methods like scoped_by_user_name(user_name) and scoped_by_user_name_and_password(user_name, password) that will use the scoped method with attributes you supply. [#1648 state:committed]
Signed-off-by: NDavid Heinemeier Hansson <david@loudthinking.com>

Signed-off-by: NPratik Naik <pratiknaik@gmail.com>

Signed-off-by: NDavid Heinemeier Hansson <david@loudthinking.com>

ActiveRecord::Base#new_record? now returns false for existing records (was nil) [#1219 state:committed]
Signed-off-by: NDavid Heinemeier Hansson <david@loudthinking.com>

Ensure Model#last doesn't affects order for another finders inside the same scope [#1499 state:resolved]
Signed-off-by: NPratik Naik <pratiknaik@gmail.com>

Signed-off-by: NDavid Heinemeier Hansson <david@loudthinking.com>

Add :having option to find, to use in combination with grouped finds. Also added to has_many and has_and_belongs_to_many associations.
Signed-off-by: NMichael Koziarski <michael@koziarski.com>
[#1028 state:committed]

Signed-off-by: NDavid Heinemeier Hansson <david@loudthinking.com>