Basics

An extension will subclass Blueprinter::Extension and define one or more hook methods. (See Blueprinter::Extension for documentation about all hooks.)

class ExcludeIfBlankExtension < Blueprinter::Extension
  def around_field_value(ctx)
    # get the value by yielding to other extensions and Blueprinter's internals
    val = yield ctx

    # skip this field and halt further extensions if the value is blank
    skip! if ctx.field.options[:exclude_if_blank] && val.blank?

    # return the value for the next extension (or Blueprinter) to use
    val
  end
end

Then add the extension to a blueprint:

class MyBlueprint < Blueprinter::V2::Base
  add ExcludeIfBlankExtension.new

  field :name, exclude_if_blank: true
end

Context Objects

All extension hooks take a single argument: a context object. It contains the “context” of the current operation (Blueprint, options, field, the object, etc.) so you can react to it and, in some cases, alter it.

There are several different context object types. See the Blueprinter::V2::Context module for documentation on which hooks receive which types, and what can be done with them.