Rails - Aug 2006 - How to show if there are children in a list?

I have the following parent - child models.

class Parent
  has_many :children
end

class Child
  belongs_to :parent, :foreign_key => "parent_id"
end



Now, in my list of parents,  the user can click a link to see the children
for a parent.  What I''d want to do is to show whether a parent has any
children on the parent list page, without the user having to click on the
link to find out.

My current query to populate the table is as follows:

@parents = Parent.find(:all, :order => "name")

Can this query be modified to get the number of children as well?  Or,
return  true if the parent has at least one child?

-- 
Best Regards,
-Larry
"Work, work, work...there is no satisfactory alternative."
            --- E.Taft Benson


--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk
-~----------~----~----~----~------~----~------~--~---

Larry Kelly wrote:
> I have the following parent - child models.
> 
> class Parent
>   has_many :children
> end
> 
> class Child
>   belongs_to :parent, :foreign_key => "parent_id"
> end
> 
> Now, in my list of parents,  the user can click a link to see the 
> children for a parent.  What I''d want to do is to show whether a
parent
> has any children on the parent list page, without the user having to 
> click on the link to find out.
> 
> My current query to populate the table is as follows:
> 
> @parents = Parent.find(:all, :order => "name")
> 
> Can this query be modified to get the number of children as well?  Or, 
> return  true if the parent has at least one child?
You can use Rails'' automatic association size caching by adding
a children_count field to the parents table, then testing whether
parent.children_count == 0.

Otherwise you''d have to add :joins, :group, and :select options to your
find call to add a attribute to each parent instance that reflects
the number of or presence of children.

-- 
We develop, watch us RoR, in numbers too big to ignore.


--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk
-~----------~----~----~----~------~----~------~--~---

In the controller:
@parents = Parent.find(:all, :order => "name", :include =>
:children)

In the view (while iterating through @parents):
<%= ''Has children'' if parent.children.any? %>
or
<%= "Has #{pluralize(parent.children.count, ''child'',
''children'')}" %>

--
Building an e-commerce site with Rails?
http://www.agilewebdevelopment.com/rails-ecommerce


On Aug 24, 2006, at 11:26 AM, Larry Kelly wrote:
> I have the following parent - child models.
>
> class Parent
>   has_many :children
> end
>
> class Child
>   belongs_to :parent, :foreign_key => "parent_id"
> end
>
>
>
> Now, in my list of parents,  the user can click a link to see the  
> children for a parent.  What I''d want to do is to show whether a  
> parent has any children on the parent list page, without the user  
> having to click on the link to find out.
>
> My current query to populate the table is as follows:
>
> @parents = Parent.find(:all, :order => "name")
>
> Can this query be modified to get the number of children as well?   
> Or, return  true if the parent has at least one child?
>
> -- 
> Best Regards,
> -Larry
> "Work, work, work...there is no satisfactory alternative."
>             --- E.Taft Benson
> >


--~--~---------~--~----~------------~-------~--~----~
You received this message because you are subscribed to the Google Groups
"Ruby on Rails: Talk" group.
To post to this group, send email to
rubyonrails-talk-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
To unsubscribe from this group, send email to
rubyonrails-talk-unsubscribe-/JYPxA39Uh5TLH3MbocFFw@public.gmane.org
For more options, visit this group at
http://groups.google.com/group/rubyonrails-talk
-~----------~----~----~----~------~----~------~--~---