Sort parents by date field in children?

[MarcC]

On the front end of a website I'm working on, I would like to sort some pages ("Project") by the nearest due date of their children. Here's an example:

Before:

Project 1

    Assignment -- Due Date 20 January 2012

    Assignment -- Due Date 21 January 2012

Project 2

    Assignment -- Due Date 18 January 2012

    Assignment -- Due Date 19 January 2012

After:

Project 2

    Assignment -- Due Date 18 January 2012

    Assignment -- Due Date 19 January 2012

Project 1

    Assignment -- Due Date 20 January 2012

    Assignment -- Due Date 21 January 2012

Any tips on a good way to do this? Thanks. I can already sort the children fine, but the parents I dunno.

[Soma]

I don't see an easy option to do that, but with a little module you could on each save of a child page update a date field on the parent. Then sort it by that field. Let us know so we can help you get started.

[Soma]

Edit well if there not too many projects you could try and evaluate the dates and store them on runtime to sort by that value afterwards when you loop them out.

$pa = $pages->find("template=project");
if(count($pa)){
    foreach($pa as $p){
        if(!$p->numChildren) continue; // no assignments
        // store a temporary value to the project page
        $p->tmp_date = $p->children("sort=-due_date")->first()->due_date;
    }
    // output the projects
    foreach($pa->sort("-tmp_date") as $p){
        echo "<li>$p->title</li>";     
        if(!$p->numChildren) continue;
        foreach($p->children("sort=-due_date") as $a){
            // output assignments
        }        
    }
}

This will work well if you don't have thousands of pages. The module approach would be the more efficient and scaleable.

[MarcC]

Thanks Soma. We won't have thousands of pages, maybe a hundred max. So I'll try the code you were kind enough to provide.

[antknight]

I had a problem here but figured it out, with Somas help