On Mon, Sep 28, 2009 at 6:07 PM, Marnen Laibow-Koser
<rails-mailing-l...@andreas-s.net> wrote:
> Patrick Doyle wrote:
>> I have the following:
>>
>> @lot = Lot.find(params[:id])
>>
>> part_nums = Part.all(:conditions => ["id <> ?", @lot.part.id])
>>
>> I guess I should mention that
>>
>> Lot :belongs_to => :part
>>
>> I was looking at the log following the execution of these two
>> statements and I saw something like this:
>>
>> Lot Load (0.4ms) SELECT * FROM "lots" WHERE ("lots"."id" = 13)
>> Part Load (0.3ms) SELECT * FROM "parts" WHERE ("parts"."id" = 2)
>> Part Load (0.9ms) SELECT * FROM "parts" WHERE (id <> 2)
>>
>> It looked a bit silly to me -- first I grab a record from the "parts"
>> table with an ID of 2, then I grab all the records from the parts
>> table whose ID is not 2.
>
> I think what's happening here is this: you're calling @lot.part.id, so
> Rails needs to load @lot.part, which accounts for the extra query. To
> fix, use the :joins option on Lot.find, or simply call @lot.part_id.
>
I should let this be, but now I'm curious... what does :joins actually
do for me?
(in script/console)
>> l=Lot.find(13, :joins => :part)
produces (in the logfile)
SELECT "lots".* FROM "lots" INNER JOIN "parts" ON "parts".id =
"lots".part_id WHERE ("lots"."id" = 13)
and that looks like what I wanted. But when I follow that up with
>> l.part
I see in the logfile:
SELECT * from "parts" WHERE ("parts"."id" = 2)
so it seems that the inner join was wasted. Is this a development vs.
production thing? (I know, I'm not supposed to worry about
optimization now, but I figure if I learn how to write generally more
optimal code by default, it will only help).
If I try:
>> l=Lot.find(13, :include => :part)
I see in the logfile:
SELECT * FROM "lots" WHERE ("lots"."id" = 13)
SELECT * FROM "parts" WHERE ("parts".id" = 2)
so neither the :joins nor the :include options seem to help, although
the :include option prevents the subsequent database access when I
finally access l.part
Again, this is not stopping me from anything, and I really should
leave the optimization phase for later, but I am curious about the
intended behavior of :include and :joins, and puzzled by the apparent
behavior.
--wpd
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