rails 3: difference between write_attribute and update_attribute

Question

I did not know about write_attribute until today...

it seems like update_attribute, although not calling validation is still calling the :before_save callbacks, whereas write_attribute doesn't.

Is that the difference between these two methods?

Answer 1

update_attribute actually makes a physical call to the DB. You get a full execution of an UPDATE statement. It's like update_attributes but just for a single column.

While write_attribute writes the attribute for assignment to the model for AR based columns. If you were to overwrite a DB based attribute.

def first_name=(val)
  write_attribute :first_name, val
end
# some_model.first_name => 'whatever val is'

def first_name=(val)
  @first_name = val
end
# some_model.first_name => nil

I have not looked into write_attribute extensively, but I gather Activerecord based models handle assignments to db based columns slightly differently than your run of the mill accessor.

Answer 2

write_attribute is used when you want to overwrite the default accessors for a method. It is essentially syntactic sugar for self[:attribute]=(value).

Have a look at the ActiveRecord::Base documentationunder the heading "Overwriting default accessors".

If you tried to rewrite the example in the documentation using update_attribute, I'd imagine it would end up in a loop.