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+---
+title: How to handle nested data in forms
+summary: Forms can save into arrays, including has_one relations
+iconBrand: wpforms
+---
+
+# How to: Save nested data
+
+## Overview
+
+Forms often save into fields `DataObject` records, through [Form::saveInto()](api:Form::saveInto()).
+There are a number of ways to save nested data into those records, including their relationships.
+
+Let's take the following data structure, and walk through different approaches.
+
+```php
+<?php
+use SilverStripe\ORM\DataObject;
+
+class Player extends DataObject
+{
+    private static $db = [
+        'Name' => 'Varchar',
+    ];
+
+    private static $has_one = [
+        'HometownTeam' => Team::class,
+    ];
+
+    private static $many_many = [
+        'Teams' => Team::class,
+    ];
+}
+```
+
+```
+<?php
+use SilverStripe\ORM\DataObject;
+
+class Team extends DataObject
+{
+    private static $db = [
+        'Name' => 'Varchar',
+    ];
+
+    private static $belongs_many_many = [
+        'Players' => Player::class,
+    ];
+}
+```
+
+## Form fields
+
+Some form fields like [MultiSelectField](api:MultiSelectField) and [CheckboxSetField](api:CheckboxSetField)
+support saving lists of identifiers into a relation. Naming the field by the relation name will
+trigger the form field to write into the relationship.
+
+Example: Select teams for an existing player
+
+```php
+<?php
+
+use SilverStripe\Control\Controller;
+use SilverStripe\Forms\CheckboxSetField;
+use SilverStripe\Forms\FieldList;
+use SilverStripe\Forms\Form;
+use SilverStripe\Forms\FormAction;
+use SilverStripe\Forms\HiddenField;
+use SilverStripe\Forms\RequiredFields;
+use SilverStripe\Forms\TextField;
+
+class MyController extends Controller
+{
+    private static $allowed_actions = ['Form'];
+
+    private static $url_segment = 'MyController';
+
+    public function Form()
+    {
+        $player = Player::get()->byID(1);
+        return Form::create(
+            $this,
+            'Form',
+            FieldList::create([
+                TextField::create('Name'),
+                CheckboxSetField::create('Teams')
+                    ->setSource(Team::get()->map()),
+                HiddenField::create('ID'),
+            ]),
+            FieldList::create([
+                FormAction::create('doSubmitForm', 'Submit')
+            ]),
+            RequiredFields::create([
+                'Name',
+                'Teams',
+                'ID',
+            ])
+        )->loadDataFrom($player);
+    }
+
+    public function doSubmitForm($data, $form)
+    {
+        $player = Player::get()->byID($data['ID']);
+
+        // Only works for updating existing records
+        if (!$player) {
+            return false;
+        }
+
+        // Check permissions for the current user.
+        if (!$player->canEdit()) {
+            return false;
+        }
+
+        // Automatically writes Teams() relationship
+        $form->saveInto($player);
+
+        $form->sessionMessage('Saved!', 'good');
+
+        return $this->redirectBack();
+    }
+}
+```
+
+
+## Dot notation
+
+For single record relationships (e.g. `has_one`),
+forms can automatically traverse into this relationship by using dot notation
+in the form field name. This also works with custom getters returning 
+`DataObject` instances. 
+
+Example: Update team name (via a `has_one` relationship) on an existing player.
+
+```php
+<?php
+
+use SilverStripe\Control\Controller;
+use SilverStripe\Forms\FieldList;
+use SilverStripe\Forms\Form;
+use SilverStripe\Forms\FormAction;
+use SilverStripe\Forms\HiddenField;
+use SilverStripe\Forms\RequiredFields;
+use SilverStripe\Forms\TextField;
+
+class MyController extends Controller
+{
+    private static $allowed_actions = ['Form'];
+
+    private static $url_segment = 'MyController';
+
+    public function Form()
+    {
+        return Form::create(
+            $this,
+            'Form',
+            FieldList::create([
+                TextField::create('Name'),
+                TextField::create('HometownTeam.Name'),
+                HiddenField::create('ID'),
+            ]),
+            FieldList::create([
+                FormAction::create('doSubmitForm', 'Submit')
+            ]),
+            RequiredFields::create([
+                'Name',
+                'HometownTeam.Name',
+                'ID',
+            ])
+        );
+    }
+
+    public function doSubmitForm($data, $form)
+    {
+        $player = Player::get()->byID($data['ID']);
+
+        // Only works for updating existing records
+        if (!$player) {
+            return false;
+        }
+
+        // Check permissions for the current user.
+        if (!$player->canEdit() || !$player->HometownTeam()->canEdit()) {
+            return false;
+        }
+
+        $form->saveInto($player);
+
+        // Write relationships *before* the original object
+        // to avoid changes being lost when flush() is called after write().
+        // CAUTION: This will create a new record if none is set on the relationship.
+        // This might or might not be desired behaviour.
+        $player->HometownTeam()->write();
+        $player->write();
+
+        $form->sessionMessage('Saved!', 'good');
+
+        return $this->redirectBack();
+    }
+}
+```
+
+## Array notation
+
+This is the most advanced technique, since it works with the form submission directly,
+rather than relying on form field logic. 
+
+Example: Create one or more new teams for existing player
+
+```
+<?php
+
+use SilverStripe\Control\Controller;
+use SilverStripe\Forms\FieldList;
+use SilverStripe\Forms\Form;
+use SilverStripe\Forms\FormAction;
+use SilverStripe\Forms\HiddenField;
+use SilverStripe\Forms\RequiredFields;
+use SilverStripe\Forms\TextField;
+
+class MyController extends Controller
+{
+    private static $allowed_actions = ['Form'];
+
+    private static $url_segment = 'MyController';
+
+    public function Form()
+    {
+        $player = Player::get()->byID(1);
+        return Form::create(
+            $this,
+            'Form',
+            FieldList::create([
+                TextField::create('Name'),
+                // The UI could duplicate this field to allow creating multiple fields
+                TextField::create('NewTeams[]', 'New Teams'),
+                HiddenField::create('ID'),
+            ]),
+            FieldList::create([
+                FormAction::create('doSubmitForm', 'Submit')
+            ]),
+            RequiredFields::create([
+                'Name',
+                'MyTeams[]',
+                'ID',
+            ])
+        )->loadDataFrom($player);
+    }
+
+    public function doSubmitForm($data, $form)
+    {
+        $player = Player::get()->byID($data['ID']);
+
+        // Only works for updating existing records
+        if (!$player) {
+            return false;
+        }
+
+        // Check permissions for the current user.
+        // if (!$player->canEdit()) {
+        //     return false;
+        // }
+
+        $form->saveInto($player);
+
+        // Manually create teams based on provided data
+        foreach ($data['NewTeams'] as $teamName) {
+            // Caution: Requires data validation on model
+            $team = Team::create()->update(['Name' => $teamName]);
+            $team->write();
+            $player->Teams()->add($team);
+        }
+
+        $form->sessionMessage('Saved!', 'good');
+
+        return $this->redirectBack();
+    }
+}
+```