Rails avoid N+1 query problem working with external and internal data

Question

I have the following array coming from an external source :

documents = ['Doc Name 1', 'Doc Name 2', 'Doc Name 3', ...]

I want to loop through the array, and find details about the documents in my db (model Doc ) if it exists.

documents.each do |document|
  puts Doc.find_by_name(document).details if Doc.find_by_name(document)
end

Of course this code works, but how can I avoid the N+1 query problem?

Answer 1

Hope details is one of the columns in the table docs (plural of the model)

Try the below:

documents = ['Doc Name 1', 'Doc Name 2', 'Doc Name 3']

Doc.where(name: documents).pluck(:details)

It will trigger single query and selects value only the column details and returns the details in an array:

SELECT "docs"."details" FROM "docs" 
  WHERE "docs"."name" IN ('Doc Name 1', 'Doc Name 2', 'Doc Name 3')

If you have more data on the array documents please consider using batch processing.