Hello,

inside the SS template i got

<% cached Children.max(LastEdited) %> 
  <% loop Children %> 
   <h3>$Title</h3>
   $Thumbnail 
  <% end_loop %> 
<% end_cached %> 

Each sub page got a thumb-nail image attached. In CMS, if i change the thumb-nail image via the UploadField, click 'Save and Publish', the 'LastEdited' field doesn't change (probably because i did not change the content of it?) and thus the change is not reviewed on the front pages. Is this a SS bug that the field 'LastEdited' not changed even though i click on the 'Save and Publish" ?

How to get around this partial caching problem?

One solution is to subclass Image, then your page can have a relation to that class instead of a relation to image. So:

class MyImage extends Image {
}

class MyPage extends Page {
    public static $has_one = array(
         'Image'=>'MyImage'
    );
}

Then in your template, you can do <% cached Children.Max(LastEdited), List(MyImage).Max(LastEdited) %>

Hope this helps

I guess List(MyImage).Max(LastEdited) will force SS to search all 'MyImage' objects in database and get the lastest LastEdited field value as part of the cache key.

The problem is: MyPage and MyImage is a many-many relation. The LastEdited field will not work because the image itself is not edited. the image is linked to another page. we just built a new link.

I guess I have to write a function to find out all the related images of the sub page and work out a key, and pass that function to SS template

class MySubPage {
   static $many_many = array('Images' =>'MyImage')
}

}

Yep, you can calculate the cache key in your controller: http://doc.silverstripe.org/framework/en/trunk/reference/partial-caching#cache-key-calculated-in-controller

I don't really know the best way to approach it, though. Perhaps you could fetch all records from the join table (e.g 'MyImage_MySubPage'), implode it to a string and md5 hash it?

That's what i thought, but then how do you 'aggregate' all the md5 strings? using max,min,avg, or sum is not going to work. I think I just concatenate all the md5 string together to build a large key.