[rspec-users] mocking a reference to a polymorphic model?

Matt Wynne matt at mattwynne.net
Thu Mar 22 20:10:46 UTC 2012


On 22 Mar 2012, at 17:27, Fearless Fool wrote:

> The basic question: how do you mock 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 references to the
> polymorphic models, but I don't see how to do that.

Can you enumerate those reasons? This doesn't seem like a good use-case for mock_model, to me.

cheers,
Matt

--
Freelance programmer & coach
Author, http://pragprog.com/book/hwcuc/the-cucumber-book
Founder, http://www.relishapp.com/
Twitter, https://twitter.com/mattwynne


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