xentronium on Five Common Rails Mistakes

Comment on Five Common Rails Mistakes parent

Do you mean something like this?

    ids = Post.where(:published => true).pluck(:id) 
    Post.where(:id => ids).delete_all

or this

    Post.where(:published => true).delete_all

?

sanderjd 14y

The second variant seems much better to me - in the first variant the size of the DELETE query itself is proportional to the number of published posts, so for very large numbers of published posts you'll end up sending a lot of data over the network, and may even hit your max_allowed_packet size (though it defaults to 1GB, which would be a lot of published posts!).

janus 14y

You might want to use 'destroy' instead of 'delete', as 'delete' skips all ActiveRecord callbacks (i. e., if you had a dependent: :destroy callback for post comments, using 'delete' would leave them intact)

xentronium 14y

`destroy` instantiates active record models which kind of defeats the purpose of fast deletion :)

janus 14y

You are right, well in that case, you would have to delete associated records manually if you didn't add any foreign keys at the db level

chris_wot 14y

I'd suggest deleting or dealing with those records anyway, regardless of whether you added FKs! But... if you don't add FKs, you've got bigger issues to deal with :(

joevandyk 14y

this is why i prefer using "on delete cascade" in schemas, no need to transmit lots of data over the wire and instantiate thousands of slow activerecord objects when deleting stuff.

randomdata 14y

Though you're still left to deal with your destroy callbacks/observers, if you have any.

chris_wot 14y

I looked up the API documentation for pluck... That definitely looks like what I'm talking about :-)

Does the second query translate to a straight DELETE?

rahoulb 14y

Yes - `delete from posts where published = 1;` (or however your particular database adapter translates true)

Comments