[ruby-on-rails] Rails filtering array of objects by attribute value

So I perform a query to the db and I have a complete array of objects:

@attachments = Job.find(1).attachments

Now that I have an array of objects I don't want to perform another db query, but I would like to filter the array based on the Attachment object's file_type so that I can have a list of attachments where the file type is 'logo' and then another list of attachments where the file type is 'image'

Something like this:

@logos  = @attachments.where("file_type = ?", 'logo')
@images = @attachments.where("file_type = ?", 'image')

But in memory instead of a db query.

This question is related to ruby-on-rails activerecord

The answer is


Try :

This is fine :

@logos = @attachments.select { |attachment| attachment.file_type == 'logo' }
@images = @attachments.select { |attachment| attachment.file_type == 'image' }

but for performance wise you don't need to iterate @attachments twice :

@logos , @images = [], []
@attachments.each do |attachment|
  @logos << attachment if attachment.file_type == 'logo'
  @images << attachment if attachment.file_type == 'image'
end

have you tried eager loading?

@attachments = Job.includes(:attachments).find(1).attachments

If your attachments are

@attachments = Job.find(1).attachments

This will be array of attachment objects

Use select method to filter based on file_type.

@logos = @attachments.select { |attachment| attachment.file_type == 'logo' }
@images = @attachments.select { |attachment| attachment.file_type == 'image' }

This will not trigger any db query.


You can filter using where

Job.includes(:attachments).where(file_type: ["logo", "image"])

I'd go about this slightly differently. Structure your query to retrieve only what you need and split from there.

So make your query the following:

#                                vv or Job.find(1) vv
attachments = Attachment.where(job_id: @job.id, file_type: ["logo", "image"])
# or 
Job.includes(:attachments).where(id: your_job_id, attachments: { file_type: ["logo", "image"] })

And then partition the data:

@logos, @images = attachments.partition { |attachment| attachment.file_type == "logo" }

That will get the data you're after in a neat and efficient manner.