Hydration with Href, ID, and Get/Reload abstraction

[displague]

WIP on #269

[displague]

If we implement a GetBasePath() string for *ServiceOp, and NewResource() interface{} // return new(Organization), we could implement Get in a ServiceOp type embedded in {Every}ServiceOp.

We would get Get and Hydrate for free (using the ServiceOp.Get implementation) in each endpoint (that uses Href and ID).

[displague]

Perhaps we could get Delete and others for free?

[t0mk]

It would be cool to have Get method for free. Just rarely there are still some resources with more than one ID param to lookup. not fitting the Get(string, *GetOptions) signature. Simple command grep -P "^\tGet\(" *go | grep string shows me only vlan assigments are the case at the moment (because I have the #302 PR checked out). But I think API keys are special too.

Then, I'm not sure how/where we'd ensure that the Get method returns the desired resource type. Right now the type is declared in the Get signature Get(DeviceID string, opts *GetOptions) (>>*Device<<, *Response, error).

So I think, for the parent interface would have to do the Hydrate method as you wrote it, and for every concrete ServiceOp we would have to implement:

• func GetResourcePath(id string) string { return path.Join(deviceBasePath, id) }
• func DefaultIncludes() []string { return []string{"facility", "hardware_reservation", "project"} } (this could be an attribute)
• func NewResource() *Device { return new(Device) }
• Get like

  // this could be copy-pasted or template-generated to all the service opts
  func (s *DeviceServiceOp) Get(id string, opts *GetOptions) (*Device, *Response, error) {
    resource := s.NewResource(s.GetResourcePath(id))        
    opts = opts.Including(s.DefaultIncludes())
    resp, err := s.Hydrate(resource, opts)
    if err != nil {
      resource = nil
    }
    return resource, resp, err
  }

[displague]

this is not needed if Device embeds *Href (https://github.com/packethost/packngo/pull/280/files#diff-ebde46360e5c028cc3bde9d49c49bfb6038d13cd340af1d2d61845323ec284fbR59-R64), as this PR does with Organization https://github.com/packethost/packngo/pull/280/files#diff-d5c3dbfdac6c7539c18385ddd9c9dceff98dfda42c0bc25acaf87135caf6e066R31

[t0mk]

I'd do the *Href embedding, it seems like a huge save on amount of code. I don't think it will break too many things as the Href field is not used so much AFAIK.