Question

I’m new to rails. Just wondering which is the better approach that will return nil if the subject_id can’t be found:

@subject = Subject.find_by_id(params[:subject_id])

or

@subject = Subject.where(:id => params[:subject_id]).first

Thanks.

Answer 1

They both generate the same SQL statement:

1.9.3p194 :003 > Example.find_by_id(9)
  Example Load (0.3ms)  SELECT "examples".* FROM "examples" WHERE "examples"."id" = 9 LIMIT 1
nil
1.9.3p194 :004 > Example.where(:id => 9).first
  Example Load (0.3ms)  SELECT "examples".* FROM "examples" WHERE "examples"."id" = 9 LIMIT 1
nil

So they’ll have the same performance characteristics at the database. There may be a slight difference in the Rails code for find_by_*_ vs. where, but I’d imagine that will be negligible compared to query time.

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Edit: In light of Ryan Bigg’s comment below, I’d have to suggest the second form for forward compatibility.