Active Record extensions

application_record.rb

class ApplicationRecord < ActiveRecord::Base
  self.abstract_class = true

  def self.inherited(child_class)
    super
    child_class.const_get('ActiveRecord_Relation').include(RelationMethods)
  end
end

relation_methods.rb

module RelationMethods
  def at(id)
    find_by(primary_key => id)
  end

  def select(*fields, **aliases)
    return super if block_given?

    table = from_clause.name ? @table.alias(from_clause.name) : @table
    fields = fields.map { |field| (Symbol === field) ? table[field] : field }
    fields += aliases.map { |(field, aliased)| table[field].as(aliased) }

    super(*fields)
  end
end

Usage:

User.select(:id, username: 'name')

User.at('1')