Question

I’ve got a quality_code field which is free-text entered by the user. However, there are certain known codes with a longer description available. If a known code is stored on the record, I would like to display the description in place of the code.

I’ve got a simple method on the model to show the description if available, or the entered quality_code if not, but it falls into the typical pattern of n+1 queries required to draw a list of n items:

def view_quality_code
  if (code = QualityCode.find_by_quality_code(quality_code)).nil?
    quality_code
  else
    code.description
  end
end

If the models were actually linked (belongs_to :quality_code) then I would sort this out by adding includes(:quality_code) to the query, so it would just do one extra query to the quality_code table.

Is there a simple way to do the same sort of thing without the models being linked?

Answer 1

Not knowing what your other model is called, I’ll pretend it’s “Widget.” Assuming you have an array of widgets like so:

widgets = Widget.all

You can fake the eager loading yourself like this:

@codes = QualityCode.where(:quality_code => widgets.map(&:quality_code).uniq).group_by(&:quality_code) 

def view_quality_code
  if codes = @codes[quality_code]
    codes[0].description
  else
    quality_code
  end
end