Silverstripe $many_many relationship with an attribute on the relationship

Question

When adding a many_many relationship much like the projects to mentors relationship in the silverstripe guide: http://doc.silverstripe.org/framework/en/tutorials/5-dataobject-relationship-management I'd like to record an attribute against the relationship. So for example "active" - yes /no field for the mentor on the project. But the mentor might have a different value for active for different projects she is related to. Whats the best way to achieve this with Silverstripe's built in tools? UPDATE with some help from IRC & the answer below. ive gotten a bit closer, bit its not working. Ive found this: https://github.com/chillu/silverstripe-framework/blob/c8136f5d4c8a37a4da274cd1c93907c0a2af86a7/docs/en/reference/grid-field.md which seems very relevant. so DebatePages have many_many panelists who can vote differently on each debate. DebatePage.php ``` private static $many_many = array( 'Panelists' => 'Panelist', 'RelationTags' => 'Tag' ); public static $many_many_extraFields = array( '…

Accepted Answer

you could use `$many_many_extraFields` on the `$many_many` relation, like this (here on the Project class I guess):

```
static $many_many = array(
    'Mentors' => 'Mentor'
);

static $many_many_extraFields = array(
    'Mentors' => array(
        'Active' => 'Boolean'
    )
);
```

Then for each Project a specific Mentor can be active or not (you can always add other fields than `'Active'`...).

If you are using SS 3.1 you can have those extra fields edited easily via a `GridField` with the `GridFieldDetailForm` component:

```
function getCMSFields(){

--[snip]--

$detailFormFields = new FieldList();
    $detailFormFields->push( new CheckBoxField(
        'ManyMany[Active]',
        'Is Mentor active?'
    ));
    $detailFormFields->push( new TextField(
        'SomeOtherField',
        'Some other title'
    ));
    $config = new GridFieldConfig_RelationEditor();
    $config->getComponentByType('GridFieldDetailForm')->setFields($detailFormFields);

$f = new GridField('Mentors', 'Mentors', $this->Mentors(), $config);
    //push() or addFieldToTab() $f to CMSFields

--[snip]--

}
```

Doc on this is here: http://doc.silverstripe.com/framework/en/3.1/reference/grid-field#customizing-detail-forms

And when retrieving the data in your code, you can use the `getExtraData($componentName, $itemID)` method on the `ManyManyList` to retrieve those extra fields values: http://api.silverstripe.org/3.1/source-class-ManyManyList.html#178-210

Silverstripe $many_many relationship with an attribute on the relationship

Solution

Problem