Querying children optimized sql?

Rails
1

Re-asking…

I have a parent with has_many children. The children have a column
‘blah’. IF I do the following:

parent.children.find_by_blah(42)

The sql exectued is:

select * from blah where parent_id = 1 and blah = 42
select * from blah where parent_id = 1

The first line of sql is what I want. The second appears to be
ActiveRecord loading up all of parent.children. This I don’t want b/c
children is huge.

How to I use ActiveRecord to find the children “by_blah” without
causing ALL children to be selected from the DB?

thanks

2

bataras wrote:

parent.children.find_by_blah(42)

The sql exectued is:

select * from blah where parent_id = 1 and blah = 42
select * from blah where parent_id = 1

The first line of sql is what I want. The second appears to be
ActiveRecord loading up all of parent.children. This I don’t want b/c
children is huge.

Somewhere later you must be referring to the naked parent.children
collection, just like in your earlier problem

http://groups.google.com/group/rubyonrails-talk/browse_thread/thread/d741810f309336a3/594abd2765f61201

–
We develop, watch us RoR, in numbers too big to ignore.

3

No i just want to use idiomatic rails to cause

select * from blah where parent_id = 1 and blah = 42

without causing rails to also do a presumptive

select * from blah where parent_id = 1

Instead of using parent.children.find_by_blah(42), should I just just
do Child.find(:all, :condition => ['parent = ? and blah = ?",
parent.id, 42] ?

Kind of funky to me.