I created a gridfield with the modul gridfieldextension to edit the records of a dataobject inline.
Unfortunately the documentation of the modul doesn't help.

I have the dataobject games which has_many goals. In the gridfield for a goal I want to edit the goals for one game. Here is a has_one with players for the player who scored the goal. But I have no idea how to put a dropdownfield for the scorer into the gridfield. Maybe someone can help.

Code for the games

<?php

class Spiele extends DataObject {
	
	private static $db = array(
	"Datum" => "Date",
	"Zeit" => "Time",
	"ToreHeim" => "Int",
	"ToreGast" => "Int",
	"Zuschauer" => "Int",
	"Gespielt" => "Boolean",
	"Stats" => "Boolean",
	"Spieldauer" => "Time"
	);
	
	private static $has_one = array(
	"Heim" => "Teams",
	"Gast" => "Teams",
	"Saison" => "Saison",
	"SpielTyp" => "SpielTyp",
	"ErgebnisArt" => "ErgebnisArt"
	);
	private static $has_many = array(
	"Tore" => "Tore",
	"Strafen" => "Strafen",
	"Aufstellung" => "Aufstellung"
	);

	private static $singular_name = "Spiel";
	private static $plural_name = "Spiele";


	static $default_sort = '';
	
	
	
	private static $searchable_fields = array(
	"Saison.Name"
	);
	
	private static $summary_fields = array(
	"Datum",
	"Zeit",
	"SpielTyp.Name",
	"Heim.Name",
	"Gast.Name"
	);
			 
function getCMSFields() {
		

		$fields = parent::getCMSFields();
		$fields->addFieldToTab("Root.Main", new CheckboxField("Gespielt","Gespielt"));
		$fields->addFieldToTab("Root.Main", new DropdownField("SpielTypID","Art des Spiels",SpielTyp::get()->Map("ID", "Name","-")));
		$fields->addFieldToTab("Root.Main", new TextField("Zuschauer","Zuschauer"));
		if ($this->SpielTypID == 1) {
		$fields->addFieldToTab("Root.Main", new DropdownField("HeimID","Heimteam",Teams::get()->Map("ID", "Name","-")));
		$fields->addFieldToTab("Root.Main", new DropdownField("GastID","Gastteam",Teams::get()->Map("ID", "Name","-")));	
		} else {
		$fields->addFieldToTab("Root.Main", new DropdownField("HeimID","Heimteam",Teams::get()->filter(array("Saison.ID" => $this->SaisonID))->Map("ID", "Name","-")->toArray(),1));
		$fields->addFieldToTab("Root.Main", new DropdownField("GastID","Gastteam",Teams::get()->filter(array("Saison.ID" => $this->SaisonID))->Map("ID", "Name","-")->toArray(),1));}
	 	$fields->addFieldToTab("Root.Main", new TextField("ToreHeim","Tore Heim"));
		$fields->addFieldToTab("Root.Main", new TextField("ToreGast","Tore Gast"));
	 	$fields->addFieldToTab("Root.Main", new CheckboxField("Stats","Stats"));
	 	$fields->addFieldToTab("Root.EigeneTore", 
		//$grid = new GridField('Tore', 'Alle Tore', Tore::get()->filter(array("SpielID" => $this->ID))->exclude('TorID', 0))
		$grid = new GridField(
    'EigeneTore',
    'Eigene Tore',
    //Tore::get()->filter(array("SpielID" => $this->ID))->exclude('TorID', 0),
    $this->Tore()->filter(array("SpielID" => $this->ID))->exclude('TorID', 0),
    GridFieldConfig::create()
		->addComponent(new GridFieldButtonRow('before'))
	    ->addComponent(new GridFieldToolbarHeader())
        ->addComponent(new GridFieldTitleHeader())
        ->addComponent(new GridFieldEditableColumns())
        ->addComponent(new GridFieldDeleteAction())
        ->addComponent(new GridFieldAddNewInlineButton())
		));
	
	$grid->getConfig()->getComponentByType('GridFieldEditableColumns')->setDisplayFields(array(
	    'TorID'  => function($record, $column, $grid) {
	        return new DropdownField($column);
	    }
	));
				
		$fields->removeFieldFromTab("Root.Main",'Spieldauer');
		$fields->removeFieldFromTab('Root', 'Tore');
	 	return $fields;
	 }
}

Code for goals

<?php

class Tore extends DataObject {
	
	private static $db = array(
	"Zeit" => "Varchar(6)",
	"Drittel" => "Int",
	"Art" => "Varchar(50)",
	"TorGegner" => "Varchar(200)",
	"A1Gegner" => "Varchar(200)",
	"A2Gegner" => "Varchar(200)",
	);
	
	private static $has_one = array(
	"Tor" => "Spieler",
	"A1" => "Spieler",
	"A2" => "Spieler",
	"TW" => "Spieler",
	"Spiel" => "Spiele",
	"Gegner" => "Teams"
	);

	private static $singular_name = "Tor";
	private static $plural_name = "Tore";


	static $default_sort = '';
	
	
	
	private static $searchable_fields = array(
	);
	
	private static $summary_fields = array(
	'Drittel',
	'Zeit',
	'Tor.Name',
	'A1.Name',
	'A2.Name',
	'TorGegner',
	'A1Gegner',
	'A2Gegner',
	'Art',
	'SpielID'
	);
			 
function getCMSFields() {
		
echo $this->SaisonID;
		$fields = parent::getCMSFields();
		$fields->addFieldToTab("Root.Main", new DropdownField("TorID","Torschütze",Spieler::get()->Map("ID", "Name","-")->toArray(),1));
		$fields->addFieldToTab("Root.Main", new DropdownField("A1ID","Assist 1",Spieler::get()->Map("ID", "Name","-")->toArray(),1));
		$fields->addFieldToTab("Root.Main", new DropdownField("A2ID","Assist 2",Spieler::get()->Map("ID", "Name","-")->toArray(),1));
		
	 	
	 	return $fields;
	 }

    public function onBeforeWrite() {
        $Team = Spiele::get()->byID($this->SpielID);
        if ($Team->Heim.Teamname == "EHC München" ){
        $this->Gegner = $Team->GastID;}
		else {
        $this->Gegner = $Team->HeimID;}
		
        parent::onBeforeWrite();
    }
}

It was easier than I thought

return new DropdownField("SpielerID", "Spieler", Spieler::get());