Order collection by first key value in serialized attribute

Question

I have a Comment model with a serialized attribute:

  serialize :edit, Hash

Each edit for the comment is timestamped by inserting a key/value pair:

self.edit[DateTime.current] = edit_content

How would I order a collection of comments, all sorted by the first submitted timestamp for each comment?

I believe the `active-model-serializers` tag is not justified here. — beauby, Oct 19 '15 at 02:46

Alexey Shein · Accepted Answer · 2015-10-04T21:49:45.847

1

You can't. Your edit column stores the data as a serialized string, so basically its contents look like this:

[3] pry(main)> a = {}
=> {}
[4] pry(main)> a[DateTime.current] = 'bla'
=> "bla"
[5] pry(main)> a[DateTime.current] = 'bla bla'
=> "bla bla"
[9] pry(main)> a.to_yaml
=> "---\n!ruby/object:DateTime 2015-10-04 21:38:02.611020000 Z: bla\n!ruby/object:DateTime 2015-10-04 21:38:06.594140000 Z: bla bla\n"
[10] pry(main)> puts a.to_yaml
---
!ruby/object:DateTime 2015-10-04 21:38:02.611020000 Z: bla
!ruby/object:DateTime 2015-10-04 21:38:06.594140000 Z: bla bla
=> nil

In order to make it sortable by database, you need either extract your edits to another entity (such as Revision and create revisions table), or, for example, make a comments.first_edit_date column and sort by it as you usually do.

P.S. You can, of course, load all your comments table to memory and then order it there, but it will have huge performance implications:

# DON'T DO THIS IN PRODUCTION
Comment.all.sort_by { |comment| comment.edit.keys.first }

edited Oct 04 '15 at 21:49

answered Oct 04 '15 at 21:42

Alexey Shein

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But I can perfectly sort each object's edit attribute by it's timestamp? `edit.keys.sort.first` – Fellow Stranger Oct 04 '15 at 21:48
You're just sorting timestamps here of one comment, that's ok. – Alexey Shein Oct 04 '15 at 21:51
Would `post.comments.sort_by { |comment| comment.edit.keys.first }` be ok in production? That would only iterate a maximum of 30 comments per post. – Fellow Stranger Oct 05 '15 at 06:51
1

If you have 1 post on the page, then yes. But it's still bad design, and if it doesn't bite you today, it will tomorrow. I'd still recommend to extract a separate model. – Alexey Shein Oct 05 '15 at 07:16

Order collection by first key value in serialized attribute

1 Answers1