Order Across Associations: Is It Possible?

[Neil C]

Imagine Parent and Child classes as you might expect:

class Parent

  include DataMapper::Resource

  property :id, Serial

  property :name, String, :required => true

  has n, :children, :order => :age.desc   #Note default order by age descending (i.e. oldest to youngest)

end

class Child

  include DataMapper::Resource

  property :id, Serial

  property :name, String, :required => true

  property :age, String, :required => true

  belongs_to :parent

end

I now want the names of the kids from oldest to youngest so I do this

parent.children.name

The problem is that the order by age descending isn't being applied; in fact, it is ignored. I am getting the names sorted by id.

Is it even possible to maintain order across associations? If so, how?

Thanks.

[Neil C]

I made a mistake in my earlier question since I just typed it out. Obviously parent.children.name wouldn't work because Collection doesn't have a name property.

So the better question is: Given the class definitions above, how would I get the names of the kids from oldest to youngest?

Thanks and sorry for the confusion.

[abu...@gmail.com]

*bump*

Did you find a solution to this Neil?

I found an old thread: https://groups.google.com/forum/?fromgroups=#!topic/datamapper/BChZ83gDSqQ

It is 3 years old now though. Is there a way to achieve this?

Cheers all....

Adam

[Neil C]

The best I could do is a hack using collect. Something like 

parent.children.collect {|child| child.name}

Whether this is sound depends on whether you have the memory for it. Otherwise, you probably have to write a native SQL query if you want to put the burden on the DB engine. Or wait for DM 2.0.

Thanks.

[abu...@gmail.com]

Thanks Neil, much obliged

[Martin Gamsjaeger]

guys, maybe this helps: http://rhnh.net/2010/12/01/ordering-by-a-field-in-a-join-model-with-datamapper

cheers

snusnu

Thanks Neil, much obliged

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