Class: Pipeloader::ProjectionExtension

Inherits:
GraphQL::Schema::FieldExtension
  • Object
show all
Defined in:
lib/pipeloader/field_exact.rb

Overview

Narrows a returned ActiveRecord::Relation to exactly the columns the query needs — and bails to a whole-row fetch the moment a selected field can’t be proven to read only known columns, so it can never raise MissingAttributeError.

Instance Method Summary collapse

Instance Method Details

#resolve(object:, arguments:, context:) ⇒ Object 



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# File 'lib/pipeloader/field_exact.rb', line 42

def resolve(object:, arguments:, context:, **)
  lookahead = arguments[:lookahead]
  inner = arguments.key?(:lookahead) ? arguments.reject { |k, _| k == :lookahead } : arguments

  # A belongs_to is loaded whole-row by `object.assoc`, so resolve it via a
  # projected query instead (still pipelined). Skipped if the type defines a
  # custom resolver, or the selection is opaque (then fall through to default).
  record = object.respond_to?(:object) ? object.object : object
  if lookahead && record.is_a?(ActiveRecord::Base) &&
     !field.owner.instance_methods(false).include?(field.resolver_method) &&
     (assoc = record.class.reflect_on_association(field.method_str.to_sym))&.belongs_to?
    fk = record.public_send(assoc.foreign_key)
    return nil if fk.nil?

    cols = Pipeloader.project_columns(assoc.klass, lookahead)
    return assoc.klass.where(assoc.klass.primary_key => fk).select(*cols).first if cols
  end

  value = yield(object, inner)
  return value unless lookahead && value.is_a?(ActiveRecord::Relation)

  cols = Pipeloader.project_columns(value.klass, lookahead)
  return value unless cols # opaque field selected -> fetch whole rows

  # Keep a has_many's foreign key so AR can still group / wire the inverse.
  if value.respond_to?(:proxy_association) && (proxy = value.proxy_association)
    cols += Array(proxy.reflection.foreign_key)
  end
  value.select(*cols.uniq)
end