Sample of Rails jbuilder template to create customized JSON output. This also shows how to access related object values and how to iterate over a has_many relationship in order to get to nested values. This is verified to work in Rail 4+ and 5rc1.

index.json.jbuilder

# app/views/controller_name/index.json.jbuilder

json.array!(@pose_blocks) do |pose_block|
  if pose_block.published == true
    json.extract! pose_block, :unique_id, :name, :pose_id_for_cover_image,  :video_duration, :video_size, :duration
    json.focus_type pose_block.focus_type.name
    json.ability_type pose_block.ability_type.name
    json.poses pose_block.pose_block_poses.each do |pose_block_pose|
      json.unique_id pose_block_pose.pose.unique_id
      json.duration pose_block_pose.duration
      json.sort_order pose_block_pose.sort_order
    end
  end
end