On Friday, August 30, 2013 8:30:32 AM UTC-7, Christian MICHON wrote:
>
> Hi,
>
> follow up on my previous post: I've now a piece of working code giving me
> the subproducts for each instance of 'Product' (using a single Sequel model
> 'Product', 2 MSSQL views and 1 many_to_many association).
>
> class Product < Sequel::Model
> set_dataset DB[:tbl_products].select(:product_id, :name)
> set_primary_key :product_id
> many_to_many :subproducts, :class=>self, :select =>
> [:tbl_products__product_id, :name], :join_table=>:tbl_sub_products,
> :left_key=>:product_id, :right_key=>:reference_product
> end
>
> I've been experimenting with eager and rcte_tree plugin. All I want is to
> be able given a product ID to get an array of products, including this top
> product and its 1st-level children. Next plans are to extract the whole
> hierarchy (descendance) for scoping purposes.
>
> Rcte_tree is out of scope now as it request to define parent as well and
> request dedicated parent_id on the table (and this is a view, out of my
> control as I'm not an admin and I am only reading out data).
>
> With eager, all I tried gave no valid output... I'm sure some eager
> loading is happening as each of the 3 following attempts get longer
> response time:
>
> >> Product.where(:product_id=>82188).eager(:subproducts).all
> => [#<Product @values={:product_id=>82188, :name=>"********"}>]
>
> >> Product.where(:product_id=>82188).eager(:subproducts=>:subproducts).all
> => [#<Product @values={:product_id=>82188, :name=>"********"}>]
>
> >>
> Product.where(:product_id=>82188).eager(:subproducts=>{:subproducts=>:subproducts}).all
> => [#<Product @values={:product_id=>82188, :name=>"********"}>]
>
This is completely expected. All eager does is automatically populate the
cached associations, it doesn't change how many records are returned by
#all. Compare the following:
Product.where(:product_id=>82188).all.map{|p| p.associations}
Product.where(:product_id=>82188).eager(:subproducts).all.map{|p|
p.associations}
Product.where(:product_id=>82188).eager(:subproducts).all.map{|p|
p.associations[:subproducts].map{|p| p.associations}}
Product.where(:product_id=>82188).eager(:subproducts=>:subproducts).all.map{|p|
p.associations[:subproducts].map{|p| p.associations}}
That being said, if you are searching for a given product_id, all is only
going to return a single record, so there is no point of eager loading if
you are just loading a single level. And if you are trying to eager load
multiple levels, you may just want to use the tactical_eager_loading
plugin, which will only use 4 queries for the following:
Product[:product_id=>82188].subproducts.each do |sp|
sp.subproducts.each do |ssp|
ssp.subproducts.each do |sssp|
end
end
end
Thanks,
Jeremy
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