Filter ActiveRecord records by nested resource logic - Rails

Question

I'm building a task list app in rails which allows user to create task lists which contain tasks. I am trying set up filtering so I can display only task lists that have all of it's tasks marked as complete.

Currently:

List model:

class List < ActiveRecord::Base
  belongs_to :user
  has_many :tasks
end

Task model:

class Task < ActiveRecord::Base
  belongs_to :list

  def completed?
    !completed_at.blank?
  end
end

As I understand it, ActiveRecord's .where query method only looks at at that model's fields and it's value (e.g: @lists.where(name: "List Name"))

Does anyone know a way of doing something similar to the pseudo code below:

@completed_lists = @lists.where(list.tasks.completed.count == list.tasks.count)

Thanks

spickermann · Accepted Answer · 2021-06-06 13:22:50Z

1

You can use this to load all lists that do not have an uncompleted task:

List.where.not(id: Task.where('completed_at IS NULL').pluck('DISTINCT list_id'))

edited Jun 6, 2021 at 13:22

answered Sep 24, 2016 at 6:45

spickermann

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3 Comments

Bartłomiej Gładys Over a year ago

It will be provide to GroupingError on postgresql. I tested it on another example :(

Bartłomiej Gładys Over a year ago

Writing group('lists.id, tasks.id') accept query on pg, but i am not sure is that work properly. What you think about this ?

spickermann Over a year ago

I change my answer

Moamen Naanou · Accepted Answer · 2016-09-24 06:25:13Z

0

Try to use List.all.map{|list| list if list.tasks.completed.count == list.tasks.count}

answered Sep 24, 2016 at 6:25

Moamen Naanou

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2 Comments

Bartłomiej Gładys Over a year ago

your solution provides to n+1.

simonlehmann Over a year ago

Thanks for the answer, it works great except the result is an array, not an ActiveRecord relation. Is there a way to convert it back to an ActiveRecord Relation?

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