Hi,
I have a Many to Many relation between myPage and myDataObject.
In the frontend I would like to sort the output descending on date LastEdited (instead of the default ascending on ID).
I'm afraid I have to use joins, but I don have any experience with that...
Could someone help me out?

Some code of what I'm trying:

class myPage extends Page{
static $many_many = array (
'myDataObject' => 'myDataObject'
);
}

class myPage_Controller extends Page_Controller{
function MyObject(){
$myobject=DataObject::get('myDataObject',.......?.......,'LastEdited DESC');
return $myobject;
}}

class myDataObject extends DataObject{
static $belongs_many_many = array(
'myPage'=>'myPage'
);
}

For this instance, the join should be generated automatically. Not sure exactly what you are trying to do, but maybe you should add something like:

"myPageID = {$this->ID}"

This should add a filter to the returned myDataObject dataobjectset to only use dataobjects linked to the current page ID. Then you can use a control loop in your template to generate whatever html you want to display the data, EG:

<% if MyObject %>
    <ul>
        <% control MyObject %>
            <li>$YouObjectVariables</li>
        <% end_control %>
    </ul>
<% end_if %>

Is that the sort of thing you were after?

Mo

Mo is right, try add the line he had written 'myPageID={$this->ID}' into your query where you have hightlighted '...............?..............'
just remember that 'myPageID' is depend on how you declared the relationship in your dataobject class. In your code it is:

static $belongs_many_many = array(
'myPage'=>'myPage'
);

if your real code is

static $belongs_many_many = array(
'BelongToMyPage'=>'myPage'
);

then in your query it would have to be 'BelongToMyPageID={$this->ID}'

Hopefully I didn't make the matter worse. ^_^

Surely the most simple solution to this is:

function getSortedmyDataObject() {
    return $this->myDataObject(null,'LastEdited DESC');
}

then in your template it is

<% control SortedmyDataObject %>
...
<% end_control %>

Hmm, I wasn't aware you could do that. Would the getSortedmyDataObject() method return a dataobjectset of all linked dataobjects?

Mo,

I believe it does return a DOS, but it might just be a component set, i'm not sure. either way, you can manipulate it as usual.

I've only used this functionality once. A little gem i discovered by just 'trying it out', not documented anywhere that i could find.

Yes, you can pass WHERE, SORT, JOIN and LIMIT as parameters in relation getters.
AFAIK these actually map to the getComponents and getManyManyComponents methods in sapphire/core/model/DataObject.php. At least that's the place I look up the parameter order when I forget it ;)

Yes, i thought as much.

Pretty useful