Allow type to be a model

[venkatd]

I don't have an idea for the best syntax but I find myself loading models from the params hash a lot. What if you were able to do something like this?

params do
    requires :user_id, identifies: User
end
get 'users/:user_id' do
   params[:user] # params calls User.find internally and raises the appropriate error if nothing is found
end

Thoughts?

[dblock]

I like it. We do the same, just a bit more explicitly with an error!(404, 'Not Found') type-thing.

[dblock]

I think the DSL should allow something more evolved, maybe

evolves :user_id, into: User, with: ActiveRecordEvolverManagerTransformer

[mbleigh]

This is definitely a common pattern and probably worth abstracting. It seems like we'd actually want to go the other way to really be describing what's happening. Something like:

requires :user, type: User, source: :user_id

I've had a convention for a long time of creating a class-level .from_param(param) method on classes that can load from URL parameters. We could look for that by default but also support a load option:

# if a symbol is passed to load, it does options[:type].send(options[:load], params[:source])
require :user, type: User, source: :user_id, load: :find_by_id
# if a lambda is passed, it passes the param to the lambda
# note that this pattern would look for anything that responds to `.call` so
# could be a class, whatever
requires :user, type: User, source: :user_id, load: ->(param){ User.find_by_id(param) }

Something more like that maybe?

[dm1try]

👍

[dblock]

@mbleigh Very nice. It makes total sense to require the loaded object vs. the source parameter. We might want to rename source to param and load to maybe just with or is it too overlapping with other places where we use similar keywords?

require :user, type: User, param: :user_id, with: :find_by_id

Furthermore, this should support a group of params or multiple params. In general the inside of that load block should have access to all params, and possibly to the entire API endpoint, I think.

[dblock]

This could also just be a block:

requires :user do
   User.find(params[:user_id]
end

[dblock]

Note that if this is implemented it might conflict with #829, so we need to find a DSL that works for both.

[rnubel]

#1039 mostly implemented this, provided you don't mind adding a ::parse method to your models:

class User < ActiveRecord::Base
  # ...
  def self.parse(param)
    find(param.to_i)
  end
end

# ...

params do
  requires :user_id, type: User
end
get do
  params[:user_id] # is a User already
end

However, it would be nice to alias params[:user] to params[:user_id] so it's less clunky in the code, but still meaningful at the API level. Maybe supporting aliases for params wouldn't be a bad idea.