Accept an option 'default' to allow setting default serialized field value if null

[mcclayton]

Included in the PR

For fields that have a value of nil, blueprinter serializes to null by default. This PR adds an ability to add a default option to blueprinter fields which can be used as the serialized value instead of null.

Before

class UserBlueprint < Blueprinter::Base
  identifier :uuid
  field :first_name
end

UserBlueprint.render(user) renders { "id": 1, "first_name": null }

After

class UserBlueprint < Blueprinter::Base
  identifier :uuid
  field :first_name, default: "N/A"
end

UserBlueprint.render(user) renders { "id": 1, "first_name": "N/A" }

Aims to address: #114

[vinaya-procore]

👍

[philipqnguyen]

Why do you need to do except(:default)?

[mcclayton]

I need to except(:default) here, because otherwise, when it makes the call through to the AutoExtractor, the AutoExtractor (with these changes) would then return the default value instead of nil. Then the association extractor would not pass the return options[:default] if value.nil? step and it would go on to call options[:blueprint].prepare(value, view_name: view, local_options: local_options). You can verify that this would fail the test for default association values.

Another option (which is closer to what you are describing) would be something like this:

def extract(association_name, object, local_options, options={})
  value = @extractor.extract(association_name, object, local_options, options)
  if (options.key?(:default) || value.nil?)
    return value
  else
    view = options[:view] || :default
    options[:blueprint].prepare(value, view_name: view, local_options: local_options)
  end
end

Thoughts?

[philipqnguyen]

OHH I see ok nevermind. I think what you have is fine.

[philipqnguyen]

Can we just let the AutoExtractor deal with the options[:default] stuff? And take it out of here?

[mcclayton]

Yeah I proposed an alternative solution above that let's the AutoExtractor do all the work necessary for defaults.

[philipqnguyen]

nevermind