Now that I'm looking at the problem again, I don't see that usage of find in the MongoDB::Collection docs. Are you sure that you don't want to use find with fields (and then either a slice or limit of the resultant cursor, possibly with a sort_by as well) or find_one instead?

What I have put together here is untested and should be considered pseudo code but it seems to me that one of the following would do the trick.

my $some_users = $collection->find->fields( { crt_by => 1, name  => 1,
+ contacts => { '$slice' => 1 } } );
#my $some_users = $collection->find->limit( 1 )->fields( { crt_by => 1
+, name  => 1, contacts => 1 } );
#my $some_users = $collection->find_one( {}, { crt_by => 1, name  => 1
+, contacts => 1 } );
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