Question

For example I’ve changed value of Post’s object and it didn’t pass validation:

my_post = Post.last
my_post.name
# => "foobar"

my_post.name = "something wrong"
my_post.save
# => (0.1ms)  begin transaction
# => (0.0ms)  rollback transaction
# => false
my_post.name
# => "something wrong"

The actual value is still “foobar”, but how can I return it now, without creating a new object?

Answer 1

changes returns a hash of the changes made to a model object:

my_post.changes["name"][0]  #=> "foobar"

This can also be accessed via the dynamically-generated method:

my_post.name_change[0]

in your case you should do

my_post.name = my_post.name_was unless my_post.save

More on this is available in the documentation for ActiveModel::Dirty.