Best way to order records by predetermined list

Question

In order to keep things simple I have avoided using an enum for an attribute, and am instead storing string values.

I have a list of all possible values in a predetermined order in the array: MyTypeEnum.names

And I have an ActiveRecord::Relation list of records in my_recs = MyModel.order(:my_type)

What is the best way to order records in my_recs by their :my_type attribute value in the order specified by the array of values in MyTypeEnum.names ?

I could try this:

my_recs = MyModel.order(:my_type)
ordered_recs = []
MyTypeEnum.names.each do |my_type_ordered|
  ordered_recs << my_recs.where(:my_type => my_type_ordered)
end

But am I killing performance by building an array instead of using the ActiveRecord::Relation? Is there a cleaner way? (Note: I may want to have flexibility in the ordering so I don't want to assume the order is hardcoded as above by the order of MyTypeEnum.names)

Answer 1

You are definitely taking a performance hit by doing a separate query for every item in MyTypeEnum . This requires only one query (grabbing all records at once).

ordered_recs = Hash[MyTypeEnum.names.map { |v| [v, []] }]

MyModel.order(:my_type).all.each do |rec|
  ordered_recs[rec.my_type] << rec
end

ordered_recs = ordered_recs.values.flatten

If MyTypeEnum contains :a , :b , and :c , ordered_recs is initialized with a Hash of Arrays keyed by each of the above symbols

irb(main):002:0> Hash[MyTypeEnum.names.map { |v| [v, []] }]
=> {:a=>[], :b=>[], :c=>[]}

The records are appended to the proper Array based on it's key in the Hash , and then when all have bene properly grouped, the arrays are concatenated/flattened together into a single list of records.