activerecord query for an array of arrays

Question

I have the following models:

Notification
  belongs_to :receiver, class_name: 'User'
  # has a sent_email boolean column default set to false

User
  has_many :received_notifications, class_name: 'Notification', foreign_key: 'receiver_id', inverse_of: :receiver
  has_one :alert

Alert
  belongs_to :user
  # has a frequency integer column

I want to grab all the notifications where the sent_email is false for all users who set their alert frequency to 1, and I want the return result to be something like this:

    [
       {user object => [<all of the notifications for user 1>]},
       {user object => [<all of the notifications for user 2>]}    
    ]

I want it to be 1 or 2 queries at most.

What would the activerecord query look like?

Arup Rakshit · Accepted Answer · 2015-06-03 15:47:52Z

2

You can use includes.

u = User.includes(:received_notifications, :alert)
        .where("alerts.frequency_discussion_alerts = ? AND notifications.sent_email = ?", 1, false)
        .references(:notifications,:alerts)

Now in batch, you can fetch users and do your job.

 u.find_each { |u| u.received_notifications }

edited Jun 3, 2015 at 15:47

answered Jun 3, 2015 at 4:43

Arup Rakshit

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8 Comments

Pavan Katepalli Over a year ago

Thanks @R_O_R but it returns all the records in a single array. Is there a way to get all the notifications for each specific reciever_id in its own array inside of an array?

Arup Rakshit Over a year ago

@PavanKatepalli Yes.. call map and build you hash.

Arup Rakshit Over a year ago

@PavanKatepalli what is your db client ? Postgresql?

Pavan Katepalli Over a year ago

The issue with .map could be that I have 20,000 notifications to map over. Do you see that being an issue?

Arup Rakshit Over a year ago

@PavanKatepalli try, .select("users.id*, notifications.*").group("users.id") ... map is not a good idea for large data.

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