From eedad00ebef73c0e6841fd8dd93232dbc4c67ce0 Mon Sep 17 00:00:00 2001
From: Loz Calver <lozcalver@bigfork.co.uk>
Date: Thu, 22 Oct 2020 15:14:15 +0100
Subject: [PATCH 1/2] NEW: Expose TreeDropdownField root node ID in schema

Forms part of a fix for silverstripe-admin#954
---
 src/Forms/TreeDropdownField.php | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/Forms/TreeDropdownField.php b/src/Forms/TreeDropdownField.php
index d51fc85f6..c884d3dcf 100644
--- a/src/Forms/TreeDropdownField.php
+++ b/src/Forms/TreeDropdownField.php
@@ -901,6 +901,7 @@ class TreeDropdownField extends FormField
         $data['data'] = array_merge($data['data'], [
             'urlTree' => $this->Link('tree'),
             'showSearch' => $this->getShowSearch(),
+            'treeBaseId' => $this->getTreeBaseID(),
             'emptyString' => $this->getEmptyString(),
             'hasEmptyDefault' => $this->getHasEmptyDefault(),
             'multiple' => false,

From 440c7cad35edb49a13547a432591b141cb7e72e1 Mon Sep 17 00:00:00 2001
From: Maxime Rainville <maxime@silverstripe.com>
Date: Fri, 23 Apr 2021 17:53:54 +1200
Subject: [PATCH 2/2] MNT Add test to cover TreeDropdownField::TreeBaseId

---
 tests/php/Forms/TreeDropdownFieldTest.php | 31 +++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/tests/php/Forms/TreeDropdownFieldTest.php b/tests/php/Forms/TreeDropdownFieldTest.php
index c06bc54d7..c9619abff 100644
--- a/tests/php/Forms/TreeDropdownFieldTest.php
+++ b/tests/php/Forms/TreeDropdownFieldTest.php
@@ -8,6 +8,8 @@ use SilverStripe\Control\Session;
 use SilverStripe\Dev\CSSContentParser;
 use SilverStripe\Dev\SapphireTest;
 use SilverStripe\Control\HTTPRequest;
+use SilverStripe\Forms\FieldList;
+use SilverStripe\Forms\Form;
 use SilverStripe\Forms\TreeDropdownField;
 use SilverStripe\ORM\Tests\HierarchyTest\TestObject;
 
@@ -246,4 +248,33 @@ class TreeDropdownFieldTest extends SapphireTest
             $result
         );
     }
+
+    public function testTreeBaseID()
+    {
+        $treeBaseID = $this->idFromFixture(Folder::class, 'folder1');
+        $field = new TreeDropdownField('TestTree', 'Test tree', Folder::class);
+
+        // getSchemaDataDefaults needs the field to be attach to a form
+        new Form(
+            null,
+            'mock',
+            new FieldList($field)
+        );
+
+        $this->assertEmpty($field->getTreeBaseID(), 'TreeBaseId does not have an initial value');
+
+        $field->setTreeBaseID($treeBaseID);
+        $this->assertEquals(
+            $treeBaseID,
+            $field->getTreeBaseID(),
+            'Value passed to setTreeBaseID is returned by getTreeBaseID'
+        );
+
+        $schema = $field->getSchemaDataDefaults();
+        $this->assertEquals(
+            $treeBaseID,
+            $schema['data']['treeBaseId'],
+            'TreeBaseId is included in the default schema data'
+        );
+    }
 }