On Martes, 5 de Octubre de 2010 12:20:15 Andrey Voronkov escribió:
> I have simple situation:
> Program ---< CustomerProgram >--- Statecustomer
>
> In ProgramsController list action I want to show virtual column named
>
> :last_statecustomer_name. So:
>
> In my ProgramsController:
> ...
> config.columns[:last_statecustomer_name].includes = [:customer_programs]
> ...
>
> In Program model:
> ...
> def last_statecustomer_name
>   customer_programs.last(:order => :date, :include =>
> [:statecustomer]).try(:statecustomer).try(:name)
> end
>
> And I'm getting N+1:
> Dcp Load (0.6ms)   SELECT `programs`.* FROM `programs` WHERE
> ((`programs`.`parent_id` IS NULL)) AND ( (`programs`.`type` = 'Dcp' )
> ) ORDER BY `programs`.`name` ASC LIMIT 0, 30
>   CustomerProgram Load (0.3ms)   SELECT `customer_programs`.* FROM
> `customer_programs` WHERE (`customer_programs`.program_id IN
> (29,10,12,24,20,15,13,26,11,28,14,16,25,19,30,21,23,32,17,27,18,8,22,9,80,1
>29,1,31,130)) CustomerProgram Columns (1.4ms)   SHOW FIELDS FROM
> `customer_programs` Rendering template within layouts/application
> Rendering list
> Rendered _list_header (42.5ms)
> Rendered _list_column_headings (36.4ms)
> Rendered _messages (2.7ms)
> Rendered _list_messages (43.3ms)
>   CustomerProgram Load (0.3ms)   SELECT * FROM `customer_programs`
> WHERE (`customer_programs`.program_id = 29) ORDER BY date DESC LIMIT 1
>   Statecustomer Columns (1.6ms)   SHOW FIELDS FROM `customers`
>   Statecustomer Load (0.2ms)   SELECT * FROM `customers` WHERE
> (`customers`.`id` = 8) AND ( (`customers`.`type` = 'Statecustomer' ) )
> Rendered _list_record_columns (67.0ms)
> Rendered _list_actions (103.8ms)
> Rendered _list_record (199.3ms)
>   CustomerProgram Load (0.2ms)   SELECT * FROM `customer_programs`
> WHERE (`customer_programs`.program_id = 10) ORDER BY date DESC LIMIT 1
>   Statecustomer Load (0.2ms)   SELECT * FROM `customers` WHERE
> (`customers`.`id` = 1) AND ( (`customers`.`type` = 'Statecustomer' ) )
> Rendered _list_record_columns (27.5ms)
> Rendered _list_actions (28.3ms)
> Rendered _list_record (58.0ms)
>   CustomerProgram Load (0.3ms)   SELECT * FROM `customer_programs`
> WHERE (`customer_programs`.program_id = 12) ORDER BY date DESC LIMIT 1
>   CACHE (0.0ms)   SELECT * FROM `customers` WHERE (`customers`.`id` =
> 8) AND ( (`customers`.`type` = 'Statecustomer' ) )
> Rendered _list_record_columns (26.2ms)
> Rendered _list_actions (27.3ms)
> Rendered _list_record (55.7ms)
>   CustomerProgram Load (0.2ms)   SELECT * FROM `customer_programs`
> WHERE (`customer_programs`.program_id = 24) ORDER BY date DESC LIMIT 1
>   Statecustomer Load (0.2ms)   SELECT * FROM `customers` WHERE
> (`customers`.`id` = 4) AND ( (`customers`.`type` = 'Statecustomer' ) )
> Rendered _list_record_columns (26.9ms)
> Rendered _list_actions (27.8ms)
> Rendered _list_record (56.9ms)
>   CustomerProgram Load (0.2ms)   SELECT * FROM `customer_programs`
> WHERE (`customer_programs`.program_id = 20) ORDER BY date DESC LIMIT 1
>   Statecustomer Load (0.2ms)   SELECT * FROM `customers` WHERE
> (`customers`.`id` = 9) AND ( (`customers`.`type` = 'Statecustomer' ) )
>
>
> What am I doing wrong?

Your include work becuase second query is loading associated customer programs 
in only one query, but later you are forcing to reload customer_programs in 
your virtual column:

customer_programs.last(:order => :date, :include => [:statecustomer])

You are passing find options to last method (order and include), so 
ActiveRecord must reload the association. You could try to set includes as 
[:customer_programs => :statescustomer] and remove arguments in last method. I 
haven't tried to set includes with a second level include but I think it 
should work (it works at :includes option of find method).
-- 
Sergio Cambra .:: entreCables S.L. ::.
Mariana Pineda 23, 50.018 Zaragoza
T) 902 021 404 F) 976 52 98 07 E) [email protected]

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