Eager load associations with Active Model Serializers

active-model-serializers, associations, eager-loading, performance, ruby-on-rails

Solution

One solution is to define your own `weeks` method on the TimecardSerializer. From there you can `.includes()` all the associations you want to eager load.

class TimecardSerializer < ActiveModel::Serializer
  embed :ids, include: true
  has_many :weeks

  def weeks
    object.weeks.includes(days: [:sub_totals, :work_periods, :adjustments])
  end
end

All the queries will still show up in the log but most will be a cached query instead of a real one.

Problem

Background I have a rails application with deeply nested associations. ``` .-< WorkPeriod Timecard -< Week -< Day -<--< Subtotal `-< Adjustment -< (has many) ``` I'm using Active Model Serializer to build out the API. On the client side I want to load a timecard and all it's associations in one shot. Currently my serializers look like this, ``` class TimecardSerializer < ActiveModel::Serializer embed :ids, include: true has_many :weeks end class WeekSerializer < ActiveModel::Serializer embed :ids, include: true has_many :days end # ... etc ... ``` Problem This all works find, except nothing gets eager-loaded. So it ends up making lots of calls to the database for each request. For each week, it makes a separate request for the days in that week. And for each day, it makes a separate request for it's work_periods, subtotals, and adjustments.

Original source