哈希/数组到活动记录

Question

I have been searching everywhere but I can't seem to find this problem anywhere. In Rails 5.0.0.beta3 I need to sort a my @record = user.records with an association and it's record. The sort goes something like this.

@record = @record.sort_by { |rec| 
If user.fav_record.find(rec.id)
  User.fav_record(rec.id).created_at
Else 
  rec.created_at
End

This is just an example of what I do. But everything sorts fine.

The problem: This returns an array and not an Active Record Class.

I've tried everything to get this to return an Active Record Class. I've pushed the sorted elements into an ID array and tried to extract it them in that order, I've tried mapping. Every result that I get turns my previous active record into an array or hash. Now I need it to go back into an active record. Does anyone know how to convert an array or hash of that active record back into an Active Record class?

Answer 1

There isn't a similarly easy way to convert ActiveRecord to array.

If you want to optimize the performance of your app, you should try to avoid converting arrays to ActiveRecord queries. Try and keep the object as a query as long as possible.

That being said, working with arrays is generally easier than queries, and it can feel like a hassle to convert a lot of array operations to ActiveRecord query (SQL) code.

It'd be better to write the sort code using ActiveRecord::Query methods or even writing it in plain SQL using find_by_sql .

I don't know what code you should specifically use here, but I do see that your code could be refactored to be clearer. First of all, If and Else should not be capitalized, but I'm assuming that this is just pseudocode and you already realize this. Second, your variable names should be pluralized if they are queries or arrays (ie @record.sort_by should be @records.sort_by instead).

It's worth mentioning that ActiveRecord queries are difficult to master and a lot of people just use array operations instead since they're easier to write. If "premature optimization is the root of all evil", it's really not the end of the world if you sacrifice a bit of performance and just keep your array implementation if you're just trying to make an initial prototype. Just make sure that you're not making "n+1" SQL calls, ie do not make a database call every iteration of your loop.

Here's an example of an array implementation which avoids the N+1 SQL issue:

# first load all the user's favorites into memory
user_fav_records = user.fav_records.select(:id, :created_at)
@records = @records.sort_by do |record|
  matching_rec = user.fav_records.find { |x| x.id.eql?(rec.id) }
  # This is using Array#find, not the ActiveRecord method
  if matching_rec
    matching_rec.created_at
  else 
    rec.created_at
  end
end

The main difference between this implementation and the code in your question is that I'm avoiding calling ActiveRecord's find each iteration of the loop. SQL read/writes are computationally expensive, and you want your code to make as little of them as possible.