Separate entities into grape-entity

[dblock]

Entites in Grape are a specialized way of representing objects. There's nothing in them that's truly grape-specific, although there's a bit of integration with parameters and such. I suggest we split entites into a new gem, much like roar or rabl.

[idyll]

I've already tried the extraction once and it seemed to work quite well. I pretty much just pulled out the code and related specs.

I am going to take a shot at this over the weekend.

Once it is working I will add you as an admin to the new project so that you can transfer it to where it should really live.

[idyll]

Okay, I've got them pulled out here:

https://github.com/agileanimal/grape-entity

with a working branch of grape here:

https://github.com/agileanimal/grape/tree/extract-entities

To finish things up we should agree on where the gem should live. Then I can update the documentation. @dblock I have added you to the repos so you can take ownership and move it if you'd like. I am also fine with maintaining this if you'd prefer.

[dblock]

This is awesome. The gem can live with you and you should totally maintain it. I am happy to help as usual. I want to make some suggestions, will make PRs and we can discuss them there.

Make a pull request for getting rid of entities inside Grape proper, please.

[idyll]

Okay I am going to iterate on this a bit. I will push the entities gem up as a starting point and try and get something really usable by the end of the week.

I think the first two goals should be improve the testability of entities and (as you noted) proper decoupling from Grape.

I like simplicity of entities for small projects so I am a bit biased - I'd prefer to leave them as the default for Grape, with the option to exclude them and replace them with another option - but lets get things to the point where they are completely decoupled and then that decision can be made.

[idyll]

Something has been bothering me since I wrote this. Hypermedia. I know Roar does this, but it doesn't fit in my world view of what an Entity does. If an Entity is a Facade on the model it shouldn't know about Hypermedia.

Hypermedia feels like it fits in more with something like a formatter. Maybe even further from the model than that.

I want the result of this to facilitate (but not require) hypermedia.

[dblock]

I've merged the PR with additional README and spec changes. We no longer require grape-entity at runtime, so this will be a breaking change for those using Entities for the next 0.3.0 release. I think it's the right thing to do.