How to present a collection of objects as a Hash keyed by an attribute value?

[Dan Hodge]

Given an Array of objects that conform to an interface like this:

Struct.new(:date, :a, :b)

I'd like to present them in JSON like this:

{ "2015-09-14": { "foo": 1, "bar": 2}, "2015-09-13": { "foo:" 3, "bar": 4 } }

I haven't found a good way in grape-entity to do this.  

This is how I'm currently handling it:

class Thing < Grape::Entity

  def self.expose_hash(options = {})

    @key_proc = options[:key]

    yield

  end

  def self.represent(objects, options = {})

    Hash[

      objects.map do |value|

        [@key_proc.call(value), new(value, options).presented]

      end

    ]

  end

  expose_hash key: proc { |obj| obj.date } do

    expose :a, as: "foo"

    expose :b, as: "bar"

  end

end

Is there a better way to do this? Would adding support for this into grape-entity be useful? I'm happy turn this into a more general solution and open a pull request if so.

thanks,

-Dan

[Daniel Doubrovkine]

In a way this is about defining a dynamic key. I think this could be useful, I'd open an issue at the very least. 

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[Dan Hodge]

I took a stab at the implementation here: https://github.com/ruby-grape/grape-entity/pull/172

Very much a work in progress but any feedback you have would be appreciated.

thanks,

-Dan