SilverStripe - DataObject to add tab and save data in Page - silverstripe

Question

I am looking to make a DataObject class which injects fields into a Page object but I'm having a bit of trouble doing so. The only solutions I've found so far require me to do something within the Page (other than adding in a relationship between the two classes), I'm not all that certain as to what I'm doing wrong...
What I need would be for the DataObject to add a tab and some fields within Page and have the data for that Page to save to the DataObjects table.
In a sense I would like them to be somewhat independent of each other, so that I can link it to Article now and then some other page types at some later date.
This is what I have so far :
Article.php
class Article extends Page {
private static $description = 'An article page for writing and posting content';
private static $has_many = array(
'MyExtraFields' => 'MyExtraFields'
);
}
The DataObject
class MyExtraFields extends DataObject {
private static $db = array(
'ExtraText' => 'Varchar(255)',
'ExtraWYSIWYG' => 'HTMLText'
);
private static $has_many = array(
'Article' => 'Article'
);
private static $summary_fields = array(
'ExtraText' => 'ExtraText',
'ExtraWYSIWYG' => 'ExtraWYSIWYG'
);
public function updateCMSFields(){
$fields = parent::getCMSFields();
$fields->addFieldsToTab('Root.Content.Translation', array(
TextField::create('ExtraText'),
HTMLEditorField::create('ExtraWYSIWYG')
)
);
return $fields;
}
}

Answer 1

If I understand it correctly, you want to be able to add the DataObject MyExtraField to the Pagetype Article. If the MyExtraField is dependent on the Article, then you need to change the Relation of the ExtraField to has_one like jberculo says:
class MyExtraField extends DataObject {
...
private static $has_one = array(
'Article' => 'Article'
);
}
Then you have to add a GridField to the Article's CMS view manage the DataObject:
class Article extends Page {
...
private static $has_many = array(
'MyExtraFields' => 'MyExtraField'
);
public function getCMSFields() {
$fields = parent::getCMSFields();
$gridFieldConfig = GridFieldConfig_RecordEditor::create();
$gridfield = new GridField( "MyExtraFields", "MyExtraField", $this->MyExtraField(), $gridFieldConfig );
$fields->addFieldToTab( 'Root.ExtraFields', $gridfield );
return $fields;
}
If you want to reuse the DataObject in different Articles, you need to use a many to many relation and a different GridField-Configuration:
$gridFieldConfig = GridFieldConfig_RelationEditor::create();
You will find the documentation of GridField here:
https://docs.silverstripe.org/en/3.4/developer_guides/forms/field_types/gridfield
If you want to manage has_one relation to be able to add just one optional instance of MyExtraField, you could use:
https://github.com/burnbright/silverstripe-hasonefield