why am I getting an extra SELECT before save! ?

rubyonrails-talk
1

In my app, I want to create a new record if it doesn't exist, and update some fields if it does.

Looking at the debug log, and it appears that I'm doing something that's causing an extra SELECT. The basic synopsis:

  sta = Station.find_by_station_id(station_id)   if sta.nil?     Station.create(params)   else     sta.p1 = "white port"     sta.p2 = "lemon juice"     sta.save!   end

The Station.create() isn't a problem. But if it takes the 'else' clause, the SQL trace looks suspicious. (Hand edited for clarity...):

2

In my app, I want to create a new record if it doesn't exist, and update some fields if it does.

Looking at the debug log, and it appears that I'm doing something that's causing an extra SELECT. The basic synopsis:

sta = Station.find_by_station_id(station_id) if sta.nil?    Station.create(params) else    sta.p1 = "white port"    sta.p2 = "lemon juice"    sta.save! end

The Station.create() isn't a problem. But if it takes the 'else' clause, the SQL trace looks suspicious. (Hand edited for clarity...):

Station Load: SELECT * FROM `stations` WHERE (`stations`.`station_id` = 'WPLJ') LIMIT 1

SQL BEGIN

Station Load: SELECT `stations`.id FROM `stations` WHERE (`stations`.`station_id` = BINARY 'WPLJ' AND `stations`.id <> 12095) LIMIT 1

Any chance you have a validates_uniqueness_of :station_id in your model? If so, the above select is checking for that.

3

Philip Hallstrom wrote:

Any chance you have a validates_uniqueness_of :station_id in your model? If so, the above select is checking for that.

Give that man a cigar! Yep, that's exactly what's going on -- thanks!

I believe it's safe to remove the uniqueness constraint since my code is checking for existence of a station before creating a new one anyway. If anyone wants to warn me of any gotcha's about doing this, now would be a good time to tell me. <grin>

- ff

4

Are you going to check for that condition *every* time you create that model? In scripts, via the console, somewhere else in the code?

If you remove that constraint you'll need to remember this every time... and at some point you'll forget. I always do :confused:

I'd leave it alone if it were me.

-p

5

Philip Hallstrom wrote:

Are you going to check for that condition *every* time you create that model? In scripts, via the console, somewhere else in the code?

If you remove that constraint you'll need to remember this every time... and at some point you'll forget. I always do :confused:

I'd leave it alone if it were me.

-p

Point well taken. Right now, that's the only code that modifies the Station table, and I'm doing a massive (initial) load and update -- removing the constraint really does speed things up. But heeding your advice, I'll reinstate the constraint after this initial load finishes. (What? Of COURSE I'll remember! :slight_smile:

Thanks.

-ff

6

:slight_smile: You could also do my_model_instance.save(false) which would bypass the validations entirely. As long as you're sure your initial data load is legit.