Fix for query bind nil bug

[sferik]

In cases where the query bind is nil, exec_explain raises the following error:

NoMethodError: undefined method `empty?' for nil:NilClass

This patch changes unless bind.empty? to unless bind.blank? and adds a test case for a nil bind.

[fxn]

Thanks :).

In principle I am hesitant to add that check, because it may hide that some code is not passing the bindings in its instrumentation call. Binds are a collection and so when no binds are used there's a collection, empty, but not nil.

There was a recent issue related to CACHE queries that I fixed in de16100 and will ship in 3.2.2. Have you seen any other use case?

[sferik]

The cases where I was seeing this error appear were all using find with an :include, for example:

User.find(
  current_user.id,
  :include => [
    :credit_card,
    :user_image,
    :sent_offers => {
      :sender => :user_image,
      :receiver => :user_image,
      :listing => [:listing_image, :listing_images]
    },
    :received_offers => {
      :sender => :user_image,
      :receiver => :user_image,
      :listing => [:listing_image, :listing_images]
    }
  ]
)

[fxn]

I cannot reproduce this failure on 3-2-stable with user has many posts. See the session:

fxn@rails:~/tmp/test-4844 $ grep threshold config/environments/development.rb 
  config.active_record.auto_explain_threshold_in_seconds = 0
fxn@rails:~/tmp/test-4844 $ script/rails c
Loading development environment (Rails 3.2.1)
1.9.3-p0 :001 > User.find(1, :include => :posts)
  User Load (3.3ms)  SELECT "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1  [["id", 1]]
  Post Load (0.5ms)  SELECT "posts".* FROM "posts" WHERE "posts"."user_id" IN (1)
  EXPLAIN (0.6ms)  EXPLAIN QUERY PLAN SELECT "users".* FROM "users" WHERE "users"."id" = ? LIMIT 1  [["id", 1]]
  EXPLAIN (0.1ms)  EXPLAIN QUERY PLAN SELECT "posts".* FROM "posts" WHERE "posts"."user_id" IN (1)
EXPLAIN for: SELECT  "users".* FROM "users"  WHERE "users"."id" = ? LIMIT 1 [["id", 1]]
0|0|0|SEARCH TABLE users USING INTEGER PRIMARY KEY (rowid=?) (~1 rows)

EXPLAIN for: SELECT "posts".* FROM "posts"  WHERE "posts"."user_id" IN (1)
0|0|0|SCAN TABLE posts (~100000 rows)
0|0|0|EXECUTE LIST SUBQUERY 1

 => #<User id: 1, created_at: "2012-01-31 07:59:45", updated_at: "2012-01-31 07:59:45"> 

Could you post a way to reproduce the error?

[iHiD]

I was just getting this issue on 3.2.1. I changed to 3-2-stable and it's fixed it. Good work.

[fxn]

@iHiD excellent, thanks very much for the feedback.

The CACHE notification have binds now (and anyway we are no longer monitoring CACHE notifications). So I think we can close this issue.

@sferik if you find this error again please feel free to reopen.

[sferik]

Sounds good. Thanks for following up.