ActiveRecord通过关联进行多个联接

Question

My customer model has many videos and videos has many video activities.

I want to join on video activities to limit based off videos that belong to a customer who has a specific email domain.

This code will give me all the video activities belonging to customer with id 52, but since videos don't have customer email, I need to join customer onto video and then do a .where.

VideoActivity.joins(:video).where(videos: {customer_id: 52})

How is this done? Doing VideoActivity.joins(:video).joins(:customer) gives me an error saying VideoActivity doesn't have a customer associated with it.

Answer 1

有很多方法可以完成此操作，并且所有方法都可以在大约同一位置结束，但是使用显式的where语句可以轻松实现此目标。

   VideoActivity.joins(:video).where("videos.customer_id = ?", 52)

Answer 2

VideoActiviy has no relation with customer, you need to say that the customer is related to the video, then it's easier to use active record's #merge that doing a hash where

VideoActivity.joins(video: :customer).merge(Customer.where('some condition'))

If you have a scope in videos you could use that too, here's an example

VideoActivity.joins(video: :customer).merge(Customer.some_scope)

PS:

a scope could be

# customer model
scope :email_ends_with, ->(string) { where('email ilike ?', "%#{string}") }

Then use it

VideoActivity.joins(video: :customer).merge(Customer.email_ends_with('gmail.com'))

Answer 3

You can write plain sql to fetch records

activities = VideoActivity.joins('INNER JOIN videos ON video_activities.video_id = videos.id INNER JOIN customers ON videos.customer_id = customers.id')
activities.where('customers.email = ?', customer_email)