This styleguide recommends best practices for API development.

Instance variables

Please do not use instance variables, there is no need for them (we don't need to access them as we do in Rails views), local variables are fine.

Entities

Always use an Entity to present the endpoint's payload.

Methods and parameters description

Every method must be described using the Grape DSL (see https://gitlab.com/gitlab-org/gitlab-ce/blob/master/lib/api/environments.rb for a good example):

desc for the method summary. You should pass it a block for additional details such as:
The GitLab version when the endpoint was added
If the endpoint is deprecated, and if so, when will it be removed
params for the method params. This acts as description, validation, and coercion of the parameters

A good example is as follows:

desc 'Get all broadcast messages' do
  detail 'This feature was introduced in GitLab 8.12.'
  success Entities::BroadcastMessage
end
params do
  optional :page,     type: Integer, desc: 'Current page number'
  optional :per_page, type: Integer, desc: 'Number of messages per page'
end
get do
  messages = BroadcastMessage.all

  present paginate(messages), with: Entities::BroadcastMessage
end

Declared params

Grape allows you to access only the parameters that have been declared by your params block. It filters out the params that have been passed, but are not allowed.

– https://github.com/ruby-grape/grape#declared

Exclude params from parent namespaces!

By default declared(params)includes parameters that were defined in all parent namespaces.

– https://github.com/ruby-grape/grape#include-parent-namespaces

In most cases you will want to exclude params from the parent namespaces:

declared(params, include_parent_namespaces: false)

When to use `declared(params)`?

You should always use declared(params) when you pass the params hash as arguments to a method call.

For instance:

# bad
User.create(params) # imagine the user submitted `admin=1`... :)

# good
User.create(declared(params, include_parent_namespaces: false).to_h)

Note: declared(params) return a Hashie::Mash object, on which you will have to call .to_h.

But we can use params[key] directly when we access single elements.