From: Paul Vudmaska <paul@...>
Date: 2004-04-16T06:28:24+09:00
Subject: Re: dbi: parent / child relationship

Kirk Haines wrote:

>On Fri, 16 Apr 2004, Paul Vudmaska wrote:
>
>  
>
>>I've got a few situations where i'm selecting a parent child 
>>relationship with a join. I'm looking for an elegant way of iterating 
>>through the children. Using the join, the parent table data is redundant 
>>when there are muliple children.
>>
>>for example, some pseudo code:
>>db.select_all('select * from parent,child where parent.id = 
>>child.idParent') .each do |r|
>>    if this_parent_id = old_parent_id
>>       #must be a child, or first parent
>>       paint_child
>>   else
>>        paint_new_parent
>>    end
>>end
>>#or this.
>>db.select_all('select id from parent').each do |r|
>>    paint_parent
>>    db.select_all('select * from child where idParent = ?,r['id']).each 
>>do |r|
>>       paint_parent
>>    end
>>end
>>
>>Neither of these is elegant or efficient. Does anyone have a more ruby 
>>way of  working with a db parent/child relationship?
>>    
>>
>
>Using Kansas, back wherever I was setting up my database handle, I'd 
>define the relationship:
>
>KSDatabase::Parent.to_many(:children, :Child, :idParent)
>
>This says to create a relationship, 'children', from Parent to Child, 
>relating the primary key of Parent to the idParent field of child.
>
>Then, to do the query and iterate:
>
># ksdbh is the Kansas object.
>ksdbh.select(:Parent).each do |parent|
>  paint_parent
>  parent.children do |child|
>    paint_child
>  end
>end
>
>
>
>Kirk Haines
>
>
>
>  
>
That sure likes like a ruby way, i'll look into Kansas, thank you.
:Paul