Rails filtering array of objects by attribute value

Question

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.

Seems like a good use case for partition - example here.

SRack
– SRack

2019-06-14 08:46:07 +00:00
Commented Jun 14, 2019 at 8:46 — SRack
– SRack, Commented Jun 14, 2019 at 8:46

Vik · Accepted Answer · 2012-04-09 11:16:39Z

192

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

answered Apr 9, 2012 at 11:16

Vik

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3 Comments

Vlad Over a year ago

As @Vik's solution is pretty much ideal, I'll just add that in binary cases, you could use a 'partition' function to make things sweet. ruby-doc.org/core-1.9.3/Enumerable.html#method-i-partition

Vik Over a year ago

Thanks @Vlad, thats cool, but it support only if we need to collect only two things from object.

Vlad Over a year ago

Yes, that's why I said "binary" :). In the question, there was apparently a choice of logo or image, so I added this for completeness.

Soundar Rathinasamy · Accepted Answer · 2012-04-09 10:22:18Z

11

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.

answered Apr 9, 2012 at 10:22

Soundar Rathinasamy

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Comments

tommasop · Accepted Answer · 2012-12-21 15:21:57Z

2

have you tried eager loading?

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

edited Dec 21, 2012 at 15:21

tommasop

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answered Apr 9, 2012 at 7:07

Siwei

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3 Comments

bsb_coffee Over a year ago

Sorry I am not being clear: how do I filter by an object attribute's value without looping through the array?

Siwei Over a year ago

If I understood correctly, you want less db query, especially, once a query such as @attachments = Job.first.attachments executed, you want to loop the @attachments meanwhile you don't want any more db queries. is this what you want to do?

bsb_coffee Over a year ago

I do a db query and receive an array of objects. I then want to create two separate lists from that one array by filtering the objects based on the value of their attributes (See original post) - cheers

prajeesh · Accepted Answer · 2021-06-10 06:24:18Z

2

For newer versions of ruby, you can use

@logos = @attachments.filter { |attachment| attachment.file_type == 'logo' }

Reference: https://apidock.com/ruby/Array/filter

answered Jun 10, 2021 at 6:24

prajeesh

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Comments

SRack · Accepted Answer · 2019-06-14 08:44:35Z

1

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.

edited Jun 14, 2019 at 8:44

answered Jun 12, 2019 at 15:07

SRack

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Comments

Darlan Dieterich · Accepted Answer · 2019-03-12 11:48:00Z

0

You can filter using where

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

answered Mar 12, 2019 at 11:48

Darlan Dieterich

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