Rails - Aug 2007 - has_many things which have many more things which... you get the idea

Say I have the following

class GrandParentThing < ActiveRecord::Base
  has_many :parent_things
end

class ParentThing < ActiveRecord::Base
  has_many :child_things
  belongs_to :grand_parent_thing
end

class ChildThing < ActiveRecord::Base
  belongs_to :parent_thing
end

Are there any built-in methods or plugins to help me get all of the child_things
that a grand_paraent_thing has?

I know how to do the .find to get the information out using a minimal number of
SQL queries but I have a lot of these in my project so I wondered if anyone had
packaged it up yet.

TIA,
Gareth


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Try acts_as_nested_set. It allows you to select all children (and
their descendents) with a single query.

http://api.rubyonrails.org/classes/ActiveRecord/Acts/NestedSet/ClassMethods.html


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You can use:
has_many :grand_child_things, :through => :parent_things

Gareth Adams wrote:
> Say I have the following
>
> class GrandParentThing < ActiveRecord::Base
>   has_many :parent_things
> end
>
> class ParentThing < ActiveRecord::Base
>   has_many :child_things
>   belongs_to :grand_parent_thing
> end
>
> class ChildThing < ActiveRecord::Base
>   belongs_to :parent_thing
> end
>
> Are there any built-in methods or plugins to help me get all of the
child_things
> that a grand_paraent_thing has?
>
> I know how to do the .find to get the information out using a minimal
number of
> SQL queries but I have a lot of these in my project so I wondered if anyone
had
> packaged it up yet.
>
> TIA,
> Gareth
>
>
> >
>   
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I think acts_as_nested_set will add more functionality than you want.
Its intent is to provide the full tree, grand_parent_thing and its
parent_things and its child_things in one collection.  It doesn''t
sound like that''s the intention here.

Use the :has_many x, :through=>y semantics.  In this case you would
add:

has_many :child_things, :through=>:parent_things

to the GrandParentClass.  With that you can refer to
grand_parent_thing.child_things and get all the children.


HTH,
AndyV


On Aug 20, 12:50 pm, Mark Thomas
<r...-gkTqyYPWbQbz1n+OaKNE4w@public.gmane.org>
wrote:
> Try acts_as_nested_set. It allows you to select all children (and
> their descendents) with a single query.
>
> http://api.rubyonrails.org/classes/ActiveRecord/Acts/NestedSet/ClassM...

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On Aug 20, 1:00 pm, AndyV <a...-HmMyXyqgL2CVc3sceRu5cw@public.gmane.org>
wrote:
> I think acts_as_nested_set will add more functionality than you want.
> Its intent is to provide the full tree, grand_parent_thing and its
> parent_things and its child_things in one collection.  It doesn''t
> sound like that''s the intention here.
It gives you a full subtree. The OP wanted to "get all of the
child_things that a grandparent_thing has" , which if you look at his
model structure, means that, given a grandparent, he wants to get all
its grandchildren. And acts_as_nested_set will do exactly that.
> Use the :has_many x, :through=>y semantics.  In this case you would
> add:
>
> has_many :child_things, :through=>:parent_things
>
> to the GrandParentClass.  With that you can refer to
> grand_parent_thing.child_things and get all the children.
Yes, this will work too. I *think* acts_as_nested_set would be more
efficient though, because it is optimized for retrieval--no joins are
needed.

-- Mark.


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Mark Thomas wrote:
> On Aug 20, 1:00 pm, AndyV
<a...-HmMyXyqgL2CVc3sceRu5cw@public.gmane.org> wrote:
>   
>> I think acts_as_nested_set will add more functionality than you want.
>> Its intent is to provide the full tree, grand_parent_thing and its
>> parent_things and its child_things in one collection.  It
doesn''t
>> sound like that''s the intention here.
>>     
>
> It gives you a full subtree. The OP wanted to "get all of the
> child_things that a grandparent_thing has" , which if you look at his
> model structure, means that, given a grandparent, he wants to get all
> its grandchildren. And acts_as_nested_set will do exactly that.
>
>   
Doesn''t acts_as_nested_set''s all_children() method return all 
descendants of a given node? Meaning that you would get all 
parent_things and child_things in the same query?

Also, according to the docs 
(http://api.rubyonrails.org/classes/ActiveRecord/Acts/NestedSet/ClassMethods.html#M000652),
acts_as_nested_set requires a full table rewrite to insert or remove a 
node.
>> Use the :has_many x, :through=>y semantics.  In this case you would
>> add:
>>
>> has_many :child_things, :through=>:parent_things
>>
>> to the GrandParentClass.  With that you can refer to
>> grand_parent_thing.child_things and get all the children.
>>     
>
> Yes, this will work too. I *think* acts_as_nested_set would be more
> efficient though, because it is optimized for retrieval--no joins are
> needed.
>
> -- Mark.
>
>
> >
>   
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