has_many association build/create method is overwrite forign_key

[suzukis]

Behavior of build / create method created has_many association differs by rails 2 and rails 3.0 and after rails3.1

class Blog < AR:Base
   has_many :entries
end
class Entry < AR:Base; end

b = Blog.create
b.id # => 1

#rails 2.3
e = b.entries.build(:blog_id => 999) 
e.blog_id # => 1
e = b.entries.create(:blog_id => 999) 
e.blog_id # => 1

#rails 3.0.11
e = b.entries.build(:blog_id => 999) 
e.blog_id # => 1
e = b.entries.create(:blog_id => 999) 
e.blog_id # => 999

#rails 3.1.3 / 3.2.1
e = b.entries.build(:blog_id => 999) 
e.blog_id # => 999
e = b.entries.create(:blog_id => 999) 
e.blog_id # => 1

[drogus]

I think that using collection.build or collection.create along with overwriting foreign_key is a bit weird. Apart from that, it would be nice to have consistent and tested behavior here and I think that it should not allow to overwrite foreign key. If you want to overwrite it, don't use collection. This may be very misleading, as you're creating a record on a collection which inf fact should not land into that collection (which may also complicate code on rails side).

I would vote for fixing it to behave like in 2.3 and throw error or show warning on try to overwrite that key.

[rohitarondekar]

If you use attr_accessible in the Entry model then you should not be able to override :blog_id using either build or create, correct?

I don't think throwing an error is a good idea. A warning would be nice. But definitely the Rails 2.3 behavior is the preferred way imho.

[byroot]

Here's a fix for that issue with test cases

[rohitarondekar]

Nice work! Tests and code looks good. I'm not familiar with the internals of AR but does has_many :through require tests too?

[byroot]

Good question, I'll check that soon.

[drogus]

/cc @tenderlove

[byroot]

@Rohit: in fact has_many :through associations are readonly unless they delegate to a belongs_to association.

So while I'm not absolutely sure, I think they are not affected by this change.