Rails - Mar 2012 - rspec: mocking a reference to a polymorphic model?

The basic question: how do you mock (or stub) a reference to a
polymorphic class in RSpec?  Trying the obvious thing leads to an error
of the form:

   undefined method `base_class'' for Post:Class

=== The details:

# file: app/models/relation.rb
class Relation < ActiveRecord::Base
  belongs_to :entity, :polymorphic => true
end

# file: db/xxx_create_relations.rb
class CreateRelations < ActiveRecord::Migration
  def change
    create_table :relations do |t|
      t.references :entity, :polymorphic => true, :null => false
    end
  end
end

# file: spec/models/relation_spec.rb
describe Relation do
  it ''should create instance without error'' do
    post = mock_model("Post")
    lambda { Relation.create!(:entity => @post)}.should_not raise_error
  end
end

=== Running the test:

  1) Relation should create instance without error
     Failure/Error: lambda { Relation.create!(:entity => post)
}.should_not raise_error
       expected no Exception, got #<NoMethodError: undefined method
`base_class'' for Post:Class>
     # ./spec/models/relation_spec.rb:39:in `block (2 levels) in <top
(required)>''

My hunch is that ActiveRecord is calling base_class on the mocked model
(Post) to determine what to stick in the ''entity_type'' column
in the
relations table.  I tried explicitly setting it, as in:

    post = mock_model("Post", :base_class => "Post")

but the error was the same.

For all the reasons that DC espouses, I''d love to mock (or stub)
references to the polymorphic models, but I don''t see how to do that.
Any ideas?

-- 
Posted via http://www.ruby-forum.com/.

-- 
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.

On Thu, Mar 22, 2012 at 7:23 AM, Fearless Fool
<lists-fsXkhYbjdPsEEoCn2XhGlw@public.gmane.org>
wrote:
> The basic question: how do you mock (or stub) a reference to a
> polymorphic class in RSpec?  Trying the obvious thing leads to an error
> of the form:
>
>   undefined method `base_class'' for Post:Class
>
> === The details:
>
> # file: app/models/relation.rb
> class Relation < ActiveRecord::Base
>  belongs_to :entity, :polymorphic => true
> end
>
> # file: db/xxx_create_relations.rb
> class CreateRelations < ActiveRecord::Migration
>  def change
>    create_table :relations do |t|
>      t.references :entity, :polymorphic => true, :null => false
>    end
>  end
> end
>
> # file: spec/models/relation_spec.rb
> describe Relation do
>  it ''should create instance without error'' do
>    post = mock_model("Post")
>    lambda { Relation.create!(:entity => @post)}.should_not raise_error
>  end
> end
>
> === Running the test:
>
>  1) Relation should create instance without error
>     Failure/Error: lambda { Relation.create!(:entity => post)
> }.should_not raise_error
>       expected no Exception, got #<NoMethodError: undefined method
> `base_class'' for Post:Class>
>     # ./spec/models/relation_spec.rb:39:in `block (2 levels) in <top
> (required)>''
>
> My hunch is that ActiveRecord is calling base_class on the mocked model
> (Post) to determine what to stick in the ''entity_type''
column in the
> relations table.  I tried explicitly setting it, as in:
>
>    post = mock_model("Post", :base_class => "Post")
>
> but the error was the same.
>
> For all the reasons that DC espouses, I''d love to mock (or stub)
> references to the polymorphic models, but I don''t see how to do
that.
> Any ideas?
I don''t espouse stubbing or mocking associations, as it requires
knowledge of Rails internals (as in your example). I do espouse
stubbing domain-specific APIs on models in controller specs, because
that provides fine-grained control of state and decoupling from the
database, but that is an entirely different matter/context.

HTH,
David

-- 
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFF+G/Ez6ZCGd0@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk+unsubscribe@googlegroups.com.
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk?hl=en.