Rails - Feb 2013 - attributes= operation *appends* instead of replacing for accepts_nested_attributes_for with has_many

When using "attributes=" for an object with a
accepts_nested_attributes_for
a model
that has a has_many relationship will cause the has_many array to be 
appended-to
instead of being replaced as would be expected by a straight assignment 
operation.

See this example:

class Member < ActiveRecord::Base
  has_many :posts
  accepts_nested_attributes_for :posts
end

class Post < ActiveRecord::Base
  belongs_to :member
end

m=Member.new
p={:name => ''joe'', :posts_attributes =>
[{:title=>''t1''},{:title=>''t2''}]}

m.attributes = p
m.posts.size ----> 2

m.attributes = p
m.posts.size ----> 4

Is this a feature or a bug?  If it is a feature, how is it supposed to be 
used?

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On Tuesday, February 26, 2013 7:35:23 PM UTC, xop wrote:
> When using "attributes=" for an object with a
accepts_nested_attributes_for a model
> that has a has_many relationship will cause the has_many array to be
appended-to
> instead of being replaced as would be expected by a straight assignment
operation.
> 
> 
attributes= has always behaved like that ( the name is bad - it''s not
really an accessor at all. The newer name is  assign_attributes)

Fred
> See this example:
> 
> 
> class Member < ActiveRecord::Base
>   has_many :posts
>   accepts_nested_attributes_for :posts
> end
> 
> 
> class Post < ActiveRecord::Base
>   belongs_to :member
> end
> 
> 
> m=Member.new
> p={:name => ''joe'', :posts_attributes =>
[{:title=>''t1''},{:title=>''t2''}]}
> 
> 
> m.attributes = p
> m.posts.size ----> 2
> 
> 
> m.attributes = p
> m.posts.size ----> 4
> 
> 
> Is this a feature or a bug?  If it is a feature, how is it supposed to be
used?
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On Tuesday, 26 February 2013 14:35:23 UTC-5, xop wrote:
>
> When using "attributes=" for an object with a 
> accepts_nested_attributes_for a model
> that has a has_many relationship will cause the has_many array to be 
> appended-to
> instead of being replaced as would be expected by a straight assignment 
> operation.
>
> See this example:
>
> class Member < ActiveRecord::Base
>   has_many :posts
>   accepts_nested_attributes_for :posts
> end
>
> class Post < ActiveRecord::Base
>   belongs_to :member
> end
>
> m=Member.new
> p={:name => ''joe'', :posts_attributes =>
[{:title=>''t1''},{:title=>''t2''}]}
>
> m.attributes = p
> m.posts.size ----> 2
>
> m.attributes = p
> m.posts.size ----> 4
>
> Is this a feature or a bug?  If it is a feature, how is it supposed to be 
> used?
>
With nested attributes, you''ll wind up creating new records unless the 
entries in :posts_attributes have an :id key which indicates they''re 
existing records to be updated.

--Matt Jones 

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