SilverStripe - limiting the number of many relations a dataobject can have - silverstripe

Question

If I have a $has_many relationship that I want to manage with a GridField in the cms, how would I go about putting a limit on the number of how many relations one object can have? Is this possible?
Can I do this in the model or would it have to be a check I add into the GridField I'm using to add and remove relations?
I'm looking at implementing GridField_SaveHandler to make a custom GridFieldComponent but not sure how I can use this to abort the save if i detect something is wrong.

Answer 1

the following 2 solutions are not the cleanest way to solve this, but the most pragmatic and easiest to implement.
basically, what I suggest to do, is just count the objects and remove the ability to add new records once the count is above a certain number.
if you want to limit the number of records on a single relation/grid (lets say max 5 players per team):
class Player extends Dataobject {
private static $db = array('Title' => 'Varchar');
private static $has_one = array('TeamPage' => 'TeamPage');
}
class TeamPage extends Page {
private static $has_one = array('Players' => 'Player');
public function getCMSFields() {
$fields = parent::getCMSFields();
$config = GridFieldConfig_RecordEditor::create();
if ($this->Players()->count > 5) {
// remove the buttons if we don't want to allow more records to be added/created
$config->removeComponentsByType('GridFieldAddNewButton');
$config->removeComponentsByType('GridFieldAddExistingAutocompleter');
}
$grid = GridField::create('Players', 'Players on this Team', $this->Players(), $config);
$fields->addFieldToTab('Root.Main', $grid);
return $fields;
}
}
if you want to limit the total number of records globally (if we limit this way to 5, this means if 1 Team already has 3 Players, then the 2nd team can only have 2):
class Player extends Dataobject {
private static $db = array('Title' => 'Varchar');
private static $has_one = array('TeamPage' => 'TeamPage');
public function canCreate($member = null) {
if (Player::get()->count() > 5) {
return false;
}
return parent::canCreate($member);
}
}
class TeamPage extends Page {
private static $has_one = array('Players' => 'Player');
public function getCMSFields() {
$fields = parent::getCMSFields();
$config = GridFieldConfig_RecordEditor::create();
$grid = GridField::create('Players', 'Players on this Team', $this->Players(), $config);
$fields->addFieldToTab('Root.Main', $grid);
return $fields;
}
}

Answer 2

I have wrote a quick jQuery plugin to limit the number of items a GridField can have: -
Download the plugin here: - gridfieldlimit.js
https://letscrate.com/f/monkeyben/silverstripe/gridfieldlimit.js
Set up the plugin in the getCMSFields function: -
// Pass GridField configs, each one containing field name and item limit
$vars = array(
"GridFieldLimits" => "[['GRIDFIELD_NAME_1', 3], ['GRIDFIELD_NAME_2', 6]]",
);
// Load the jquery gridfield plugin
Requirements::javascriptTemplate("themes/YOUR_THEME_NAME/javascript/gridfieldlimit.js", $vars);

Answer 3

works for me: make the canCreate method of the DataObject that's managed by your GridField check for existing objects.
of course, this doesn't allow you to implement a customg GridFieldComponent, as you need to modify the DataObject code.