Question! Entities vs. Models about grape

[dblock]

@micahbrich: we do the same thing as you - I think it would be great if we could use this model as a mixin.

[mbleigh]

So the reason for the difference is because I think there's actually an important idea in separating your representation from your model, but I'm not one to make other people's decisions for them.

I will likely convert the Entity code into a module and simply use bare classes with the module included to achieve the separation I want. Stay tuned in the next week or so for this.

[micahbrich]

That's cool, that sounds like the best of both! How come it's good to separate em, is there a lesson I could learn from that? What are the benefits?

So the reason for the difference is because I think there's actually an important in separating your representation from your model, but I'm not one to make other people's decisions for them.

I will likely convert the Entity code into a module and simply use bare classes with the module included to achieve the separation I want. Stay tuned in the next week or so for this.

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#73 (comment)

[jch]

@micahbrich my argument for keeping them separate is that it's a better separation of concerns. The model is responsible for validating and persisting the data. I see Entities as a representation of a model (similar to a database view, or a rails view). Using your User model as an example, you might want to make multiple different Entities that represent the same User instance in different ways:

# if you are friend, I can see all of your fields
class FriendEntity < Grape::Entity
  expose :email, :username, :firstname, :lastname
end

# if you are Foe, I can only see your username
class FoeEntity < Grape::Entity
  expose :username
end

Then your model doesn't have to have conditionals sprinkled around to determine what to display. Your API endpoint can be responsible for figuring out which representation to display:

class API < Grape::API
  get '/users/:id' do
    user = User.find(params[:id])
    representation = current_user.friends_with?(user) ? FriendEntity : FoeEntity
    present user, :with => represenation
  end
end

[micahbrich]

Ohhh that's fascinating, I never thought of it like that. Thanks @jch!

[windmillium]

@micahbrich This is the S in SOLID, when you mix view logic into your model you give it multiple reasons to change, which leads to skyrocketing complexity, as @jch points out.

http://en.wikipedia.org/wiki/Single_responsibility_principle

[jch]

Sandi Metz gave a great conference talk that explains SOLID step by step. The video is available here

[dblock]

Lets close this since it's a question. Bring it up in the Google Group for followup.