LookupField value handling corrected (atomic values are no longer thrown away).

src/Forms/LookupField.php

@@ -8,9 +8,9 @@ use SilverStripe\ORM\DataObjectInterface;
 use SilverStripe\ORM\FieldType\DBField;
 
 /**
- * Read-only complement of {@link DropdownField}.
+ * Read-only complement of {@link MultiSelectField}.
  *
- * Shows the "human value" of the dropdown field for the currently selected
+ * Shows the "human value" of the MultiSelectField for the currently selected
  * value.
  */
 class LookupField extends MultiSelectField

src/Forms/SingleLookupField.php

@@ -0,0 +1,134 @@
+<?php
+
+namespace SilverStripe\Forms;
+
+use SilverStripe\Core\Convert;
+use SilverStripe\ORM\DataObjectInterface;
+use SilverStripe\ORM\Map;
+use SilverStripe\ORM\FieldType\DBField;
+
+/**
+ * Read-only complement of {@link DropdownField}.
+ *
+ * Shows the "human value" of the dropdown field for the currently selected
+ * value.
+ */
+class SingleLookupField extends SingleSelectField
+{
+    /**
+     * @var bool
+     */
+    protected $readonly = true;
+
+    /**
+     * @return mixed|null
+     */
+    protected function valueToLabel()
+    {
+        $value = $this->value;
+        $source = $this->getSource();
+        $source = ($source instanceof Map) ? $source->toArray() : $source;
+
+        if (array_key_exists($value, $source)) {
+            return $source[$value];
+        }
+
+        return null;
+    }
+
+    /**
+     * Ignore validation as the field is readonly
+     *
+     * @param Validator $validator
+     * @return bool
+     */
+    public function validate($validator)
+    {
+        return true;
+    }
+
+    /**
+     * Stubbed so invalid data doesn't save into the DB
+     *
+     * @param DataObjectInterface $record DataObject to save data into
+     */
+    public function saveInto(DataObjectInterface $record)
+    {
+    }
+
+    /**
+     * @return SingleLookupField
+     */
+    public function performReadonlyTransformation()
+    {
+        $clone = clone $this;
+
+        return $clone;
+    }
+
+    /**
+     * @return bool
+     */
+    public function getHasEmptyDefault()
+    {
+        return false;
+    }
+
+    /**
+     * @return string
+     */
+    public function Type()
+    {
+        return 'single-lookup readonly';
+    }
+
+    /**
+     * Note: we need to transform value in here becaue React fields do not use Field() to display value
+     *
+     * @return mixed
+     */
+    public function Value()
+    {
+        $label = $this->valueToLabel();
+        if (!is_null($label)) {
+            return $label;
+        }
+
+        return $value;
+    }
+
+    /**
+     * @return string
+     */
+    public function getTemplate()
+    {
+        // this field uses the same default template as LookupField
+        return parent::getTemplate() ?: LookupField::class;
+    }
+
+    /**
+     * Returns a readonly span containing the correct value.
+     *
+     * @param array $properties
+     *
+     * @return string
+     */
+    public function Field($properties = [])
+    {
+        $label = $this->valueToLabel();
+        if (!is_null($label)) {
+            $attrValue = Convert::raw2xml($label);
+            $inputValue = $this->value;
+        } else {
+            $attrValue = '<i>(' . _t('SilverStripe\\Forms\\FormField.NONE', 'none') . ')</i>';
+            $inputValue = '';
+        }
+
+        $properties = array_merge($properties, array(
+            'AttrValue' => DBField::create_field('HTMLFragment', $attrValue),
+            'InputValue' => $inputValue
+        ));
+
+        return parent::Field($properties);
+    }
+}

src/Forms/SingleSelectField.php

@@ -160,4 +160,17 @@ abstract class SingleSelectField extends SelectField
         }
         return $field;
     }
+
+    /**
+     * @return SingleLookupField
+     */
+    public function performReadonlyTransformation()
+    {
+        /** @var SingleLookupField $field */
+        $field = $this->castedCopy(SingleLookupField::class);
+        $field->setSource($this->getSource());
+        $field->setReadonly(true);
+
+        return $field;
+    }
 }

tests/php/Forms/SingleLookupFieldTest.php

@@ -0,0 +1,47 @@
+<?php
+
+namespace SilverStripe\Forms\Tests;
+
+use SilverStripe\Forms\SingleLookupField;
+use SilverStripe\Dev\SapphireTest;
+use SilverStripe\Forms\DropdownField;
+
+/**
+ * Class SingleLookupFieldTest
+ *
+ * @package SilverStripe\Forms\Tests
+ */
+class SingleLookupFieldTest extends SapphireTest
+{
+    public function testValueFromSource()
+    {
+        /** @var SingleLookupField $testField */
+        $testField = DropdownField::create(
+            'FirstName',
+            'FirstName',
+            ['member1' => 'Member 1', 'member2' => 'Member 2', 'member3' => 'Member 3']
+        )->performReadonlyTransformation();
+
+        $this->assertInstanceOf(SingleLookupField::class, $testField);
+
+        $testField->setValue('member1');
+        preg_match('/Member 1/', $testField->Field(), $matches);
+        $this->assertEquals($matches[0], 'Member 1');
+    }
+
+    public function testValueNotFromSource()
+    {
+        /** @var SingleLookupField $testField */
+        $testField = DropdownField::create(
+            'FirstName',
+            'FirstName',
+            ['member1' => 'Member 1', 'member2' => 'Member 2', 'member3' => 'Member 3']
+        )->performReadonlyTransformation();
+
+        $this->assertInstanceOf(SingleLookupField::class, $testField);
+
+        $testField->setValue('member123');
+        preg_match('/\(none\)/', $testField->Field(), $matches);
+        $this->assertEquals($matches[0], '(none)');
+    }
+}