create_attribute before save in Rails 3.1 doesn't set self.attribute_id

Old code, working in Rails 3.0:

belongs_to :primary_stream

before_save :autocreate_primary_stream, :if=>lambda {|a| a.primary_stream.nil?}

def autocreate_primary_stream
  self.create_primary_stream()
end

In Rails 3.1: self.primary_stream is populated, and self.primary_stream_id is nil. When the record is saved, the primary_stream_id is saved as nil to the database.

I've had to do this, to get the behaviour I would expect:

belongs_to :primary_stream

before_save :autocreate_primary_stream, :if=>lambda {|a| a.primary_stream.nil?}

def autocreate_primary_stream
  self.create_primary_stream()
  self.primary_stream_id = primary_stream.id
end

Has something changed, or have I done something 开发者_StackOverflow社区very silly?

It seems like there may be a bug in the way Rails handles association-creation in callbacks, introduced in 3.1. As far as I can tell, assigning a belongs-to association in before_save won't assign the foreign key to the owner model.

However, the autosaving-association stuff in 3.1 gives a cleaner way of achieving this -

belongs_to :primary_stream

before_validation :autocreate_primary_stream, :if=>lambda {|a| a.primary_stream.nil?}

def autocreate_primary_stream
  self.build_primary_stream()
end

and the primary stream will be auto-saved along with the owner record.

https://github.com/rails/rails/issues/1594 was somewhat relevant.