Fix issue processwire/processwire-issues#1649

wire/core/Field.php

@@ -38,6 +38,7 @@
  * @property array $allowContexts Names of settings that are custom configured to be allowed for context. #pw-group-properties
  * @property bool|int|null $flagUnique Non-empty value indicates request for, or presence of, Field::flagUnique flag. #pw-internal
  * @property Fieldgroup|null $_contextFieldgroup Fieldgroup field is in context for or null if not in context. #pw-internal
+ * @property true|null $distinctAutojoin When true and flagAutojoin is set, a distinct autojoin will be used. 3.0.208+ #pw-internal
  *
  * Common Inputfield properties that Field objects store:  
  * @property int|bool|null $required Whether or not this field is required during input #pw-group-properties
@@ -812,7 +813,7 @@ class Field extends WireData implements Saveable, Exportable {
 				$ids[] = (int) $role->id;
 			} else if(is_string($role) && strlen($role)) {
 				$rolePage = $this->wire()->roles->get($role); 
-				if($rolePage && $rolePage->id) {
+				if($rolePage instanceof Role && $rolePage->id) {
 					$ids[] = $rolePage->id;
 				} else {
 					$this->error("Unknown role '$role'"); 

wire/core/FieldtypeMulti.php

@@ -875,6 +875,7 @@ abstract class FieldtypeMulti extends Fieldtype {
 		$schema = $this->trimDatabaseSchema($this->getDatabaseSchema($field)); 
 		$fieldName = $this->database->escapeCol($field->name); 
 		$separator = self::multiValueSeparator; 
+		if($field->distinctAutojoin) $table = "DISTINCT $table";
 		foreach($schema as $key => $unused) {
 			$query->select("GROUP_CONCAT($table.$key SEPARATOR '$separator') AS `{$fieldName}__$key`"); // QA
 		}		

wire/core/PagesLoader.php

@@ -629,6 +629,7 @@ class PagesLoader extends Wire {
 		$languages = $this->wire()->languages;
 		$languageIds = array();
 		$templatesById = array();
+		$tmpAutojoinFields = array(); // fields to autojoin temporarily, just during this method call
 
 		if($languages) foreach($languages as $language) $languageIds[$language->id] = $language->id;
 		
@@ -706,15 +707,21 @@ class PagesLoader extends Wire {
 				}
 			}
 			
-			// set blank values where joinField didn't appear on page row 
 			foreach($joinFields as $joinField) {
-				if(isset($row["{$joinField}__data"])) continue;
 				if(empty($joinResults[$joinField])) continue; // field did not support autojoin
 				if(!$template->fieldgroup->hasField($joinField)) continue;
 				$field = $page->getField($joinField);
 				if(!$field || !$field->type) continue;
-				$blankValue = $field->type->getBlankValue($page, $field);
+				if(isset($row["{$joinField}__data"])) {
-				$page->setFieldValue($field->name, $blankValue, false);
+					if(!$field->hasFlag(Field::flagAutojoin)) {
+						$field->addFlag(Field::flagAutojoin);
+						$tmpAutojoinFields[$field->id] = $field;
+					}
+				} else {
+					// set blank values where joinField didn't appear on page row 
+					$blankValue = $field->type->getBlankValue($page, $field);
+					$page->setFieldValue($field->name, $blankValue, false);
+				}
 			}
 
 			$page->setIsLoaded(true);
@@ -731,6 +738,10 @@ class PagesLoader extends Wire {
 		$pageArray->setTotal($paginationTotal);
 		$pageArray->resetTrackChanges(true);
 		
+		foreach($tmpAutojoinFields as $field) { /** @var Field $field */
+			$field->removeFlag(Field::flagAutojoin)->untrackChange('flags');
+		}
+		
 		if($useCache) {
 			$selectorString = $pageArray->getSelectors(true);
 			$this->pages->cacher()->selectorCache($selectorString, $options, $pageArray);

wire/modules/Fieldtype/FieldtypePage.module

@@ -914,6 +914,19 @@ class FieldtypePage extends FieldtypeMulti implements Module, ConfigurableModule
 		return $query;
 	}
 
+	/**
+	 * Return the query used for Autojoining this field
+	 *
+	 * @param Field $field
+	 * @param DatabaseQuerySelect $query
+	 * @return DatabaseQuerySelect|null
+	 *
+	 */
+	public function getLoadQueryAutojoin(Field $field, DatabaseQuerySelect $query) {
+		$field->setQuietly('distinctAutojoin', true);
+		return parent::getLoadQueryAutojoin($field, $query);
+	}
+
 	/**
 	 * Update a DatabaseQuerySelect object to match a Page
 	 *