What is the best way to check if a record exists before 'creating' the object?
@tag = Tag.find_by_name(tag)
if @tag
do_something
else
do_something_else
end
Can you do:
if @tag = Tag.find_by_name(tag)
do_something
else
do_something_else
end
-
I like first approach..Arup Rakshit– Arup Rakshit2014-01-27 14:29:08 +00:00Commented Jan 27, 2014 at 14:29
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1 Answer
Both versions are perfectly fine. It's very common to use the latter, because it's more concise. However, for readability, you may want to use
if (@tag = Tag.find_by_name(tag))
This is not necessary, but it makes it more explicit that you are doing an assignment and not a comparison.
if @tag == Tag.find_by_name(tag)
Wrapping it into parenthesis is more explicit. It says, assign, then evaluate the result.
Furthermore, if you don't actually need the tag object itself, and you just care for the existence, you may want to use exist?
if Tag.exists?(name: tag)
This is faster, because it uses a SELECT COUNT SQL query and not a full SELECT. It basically doesn't instantiate the record.
3 Comments
the Tin Man
+1 Assigning in a conditional test is a maintenance bug in waiting; People do it in C and Perl, but unless it's well commented, someone following along might not understand that it's SUPPOSED to be an assignment instead of a comparison. It's better to assign in a previous step, then compare, which makes it a lot more obvious what the intention was.
grabury
Thanks Simon. Tag.exists?(name: tag) worked for me and Tag.where(name: tag).exist? did not. Any idea why the difference in syntax?
Simone Carletti
The syntax may have changed, I should look at the API.