FIX Add extraEmptyValues to TreedropdownField

src/Forms/RequiredFields.php

@@ -116,8 +116,15 @@ public function php($data)
                     $error = (count($value ?? [])) ? false : true;
                 }
             } else {
-                // assume a string or integer
-                $error = (strlen($value ?? '')) ? false : true;
+                $stringValue = (string) $value;
+                if ($formField instanceof TreeDropdownField) {
+                    // test for blank string as well as '0' because older versions of silverstripe/admin FormBuilder
+                    // forms created using redux-form would have a value of null for unsaved records
+                    // the null value will have been converted to '' by the time it gets to this point
+                    $error = in_array($stringValue, ['0', '']);
+                } else {
+                    $error = strlen($stringValue) > 0 ? false : true;
+                }
             }
 
             if ($formField && $error) {

src/Forms/TreeDropdownField.php

@@ -249,7 +249,12 @@ public function __construct(
 
         $this->addExtraClass('single');
 
-        parent::__construct($name, $title);
+        // Set a default value of 0 instead of null
+        // Because TreedropdownField requires SourceObject to have the Hierarchy extension, make the default
+        // value the same as the default value for a RelationID, which is 0.
+        $value = 0;
+
+        parent::__construct($name, $title, $value);
     }
 
     /**
@@ -981,4 +986,16 @@ public function setShowSelectedPath($showSelectedPath)
         $this->showSelectedPath = $showSelectedPath;
         return $this;
     }
+
+    /**
+     * @return array
+     */
+    public function getSchemaValidation()
+    {
+        $validationList = parent::getSchemaValidation();
+        if (array_key_exists('required', $validationList)) {
+            $validationList['required'] = ['extraEmptyValues' => ['0']];
+        }
+        return $validationList;
+    }
 }

tests/php/Forms/RequiredFieldsTest.php

@@ -4,14 +4,16 @@
 
 use SilverStripe\Dev\SapphireTest;
 use SilverStripe\Forms\RequiredFields;
+use SilverStripe\Forms\Form;
+use SilverStripe\Forms\TreeDropdownField;
+use SilverStripe\Security\Group;
 
 /**
  * @todo Test the validation method php()
  * @skipUpgrade
  */
 class RequiredFieldsTest extends SapphireTest
 {
-
     public function testConstructingWithArray()
     {
         //can we construct with an array?
@@ -290,4 +292,18 @@ public function testFieldIsRequired()
             "Unexpectedly returned true for a non-existent field"
         );
     }
+
+    public function testTreedropFieldValidation()
+    {
+        $form = new Form();
+        $field = new TreeDropdownField('TestField', 'TestField', Group::class);
+        $form->Fields()->push($field);
+        $validator = new RequiredFields('TestField');
+        $validator->setForm($form);
+        // blank string and '0' are fail required field validation
+        $this->assertFalse($validator->php(['TestField' => '']));
+        $this->assertFalse($validator->php(['TestField' => '0']));
+        // '1' passes required field validation
+        $this->assertTrue($validator->php(['TestField' => '1']));
+    }
 }

tests/php/Forms/TreeDropdownFieldTest.php

@@ -10,6 +10,7 @@
 use SilverStripe\Control\HTTPRequest;
 use SilverStripe\Forms\FieldList;
 use SilverStripe\Forms\Form;
+use SilverStripe\Forms\RequiredFields;
 use SilverStripe\Forms\TreeDropdownField;
 use SilverStripe\ORM\DataObject;
 use SilverStripe\ORM\Tests\HierarchyTest\HierarchyOnSubclassTestObject;
@@ -52,6 +53,22 @@ public function testSchemaStateDefaults()
         );
     }
 
+    public function testGetSchemaValidation(): void
+    {
+        // field is not required
+        $field = new TreeDropdownField('TestTree', 'Test tree', Folder::class);
+        $expected = [];
+        $this->assertSame($expected, $field->getSchemaValidation());
+        // field is required
+        $fieldList = new FieldList([$field]);
+        $validator = new RequiredFields('TestTree');
+        new Form(null, null, $fieldList, null, $validator);
+        $expected = [
+            'required' => ['extraEmptyValues' => ['0']],
+        ];
+        $this->assertSame($expected, $field->getSchemaValidation());
+    }
+
     public function testTreeSearchJson()
     {
         $field = new TreeDropdownField('TestTree', 'Test tree', Folder::class);