Rails - Apr 2007 - After loading model, can it be again accessed without SQL...

Quick question:

1 User -> many Accounts

If I eager load the user with: my_user = User.find(:first, include =>
[:accounts])

How can I then use criteria to work with the "accounts" without making
another query to the database?

Iteration is one option, but it would be best to avoid it if say I
wanted one of the accounts in the user by :name => "Checking
Account".

Thanks a lot of any advice.

Kendall Buchanan

-- 
Posted via http://www.ruby-forum.com/.

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> Quick question:
> 
> 1 User -> many Accounts
> 
> If I eager load the user with: my_user = User.find(:first, include =>
> [:accounts])
> 
> How can I then use criteria to work with the "accounts" 
> without making another query to the database?
> 
> Iteration is one option, but it would be best to avoid it if 
> say I wanted one of the accounts in the user by :name => 
> "Checking Account".
I don''t think you can. However, you might be able to do it another way.
If you know before the load which one account you want to look at, you
could do:

User.find(:first, :include=>[:accounts],
:conditions=>[''accounts.name ?'', ''Checking
Account''])

perhaps a bit less efficient than including the condition in the JOIN
itself, but it ought to work. Note that this will only work properly if
you''re only :including one relationship with many entities.

An alternate solution might be to include the condition in a manual
join:

User.find(:first, :joins=>''LEFT OUTER JOIN accounts on
accounts.user_id
= users.id AND accounts.name = ''Checking Account'')

then the account properties will appear on the user object, but I dunno
what will happen if the user and account objects share any property
names, nor do I know if the automatic sql type->ruby type mappings will
occur as usual.

- donald

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from what i know that''s no problem at all ?!? that''s the whole
point
of eager loading....

@user = User.find(:first, include => [:accounts])

@user.accounts.find(blablaba-)
@user.accounts.each do { |account| blablabla }
@user.accounts.count

these and more will workwithout re-querying the database. basically
any AR method you use on @user.accounts won''t hit the database, except
for updating/adding/removing an account, of course.

On 16 Apr., 18:35, "Ball, Donald A Jr \(Library\)"
<donald.b...-GjtI+QwuxAR68HQyEA6aog@public.gmane.org>
wrote:
> > Quick question:
>
> > 1 User -> many Accounts
>
> > If I eager load the user with: my_user = User.find(:first, include
=>
> > [:accounts])
>
> > How can I then use criteria to work with the "accounts"
> > without making another query to the database?
>
> > Iteration is one option, but it would be best to avoid it if
> > say I wanted one of the accounts in the user by :name =>
> > "Checking Account".
>
> I don''t think you can. However, you might be able to do it another
way.
> If you know before the load which one account you want to look at, you
> could do:
>
> User.find(:first, :include=>[:accounts],
:conditions=>[''accounts.name > ?'', ''Checking
Account''])
>
> perhaps a bit less efficient than including the condition in the JOIN
> itself, but it ought to work. Note that this will only work properly if
> you''re only :including one relationship with many entities.
>
> An alternate solution might be to include the condition in a manual
> join:
>
> User.find(:first, :joins=>''LEFT OUTER JOIN accounts on
accounts.user_id
> = users.id AND accounts.name = ''Checking Account'')
>
> then the account properties will appear on the user object, but I dunno
> what will happen if the user and account objects share any property
> names, nor do I know if the automatic sql type->ruby type mappings will
> occur as usual.
>
> - donald

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> from what i know that''s no problem at all ?!? that''s the 
> whole point of eager loading....
> 
> @user = User.find(:first, include => [:accounts])
> 
> @user.accounts.find(blablaba-)
> @user.accounts.each do { |account| blablabla } @user.accounts.count
> 
> these and more will workwithout re-querying the database. 
> basically any AR method you use on @user.accounts won''t hit 
> the database, except for updating/adding/removing an account, 
> of course.
My understand was that he was trying to query the eagerly loaded user''s
accounts using SQL conditions, which AFAIK you cannot do without
requerying the database. Sure, you can iterate through and find the
account named ''Checking Account'', but it''s probably
faster to have the
database do the work for you.

For a handful of accounts and a simple criteria like this, it''s almost
certainly 6 == 1/2 dozen and I''d probably do it all in ruby for
clarity,
but if there are many children and complex criteria, I''d do it in SQL.

- donald

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