MDL-15070 dml: recordset rewinding now forbidden - not all databases support it, sorry

lib/dml/adodb_moodle_recordset.php

@@ -27,10 +27,6 @@ class adodb_moodle_recordset extends moodle_recordset {
         $this->rs->MoveNext();
     }
 
-    public function rewind() {
-        $this->rs->MoveFirst();
-    }
-
     public function valid() {
         return !$this->rs->EOF;
     }

lib/dml/moodle_recordset.php

@@ -31,10 +31,13 @@ abstract class moodle_recordset implements Iterator {
     //public abstract function next();
 
     /**
-     * Revinds back to the first row
+     * Revinds are not supported!
      * @return void
      */
-    //public abstract function rewind();
+    public function rewind() {
+        // no seeking, sorry - let's ignore it ;-)
+        return;
+    }
 
     /**
      * Did we reach the end?

lib/dml/mysqli_native_moodle_recordset.php

@@ -40,10 +40,6 @@ class mysqli_native_moodle_recordset extends moodle_recordset {
         $this->current = $this->fetch_next();
     }
 
-    public function rewind() {
-        // we can not seek, sorry - let's ignore it ;-)
-    }
-
     public function valid() {
         return !empty($this->current);
     }

lib/dml/pdo_moodle_recordset.php

@@ -34,13 +34,6 @@ class pdo_moodle_recordset extends moodle_recordset {
         return $this->fields !== false;
     }
 
-    public function rewind() {
-        $this->fields = $this->sth->fetch();
-        if ($this->fields) {
-            $this->rowCount = 0;
-        }
-    }
-
     public function valid() {
         if($this->rowCount < 0) {
             $this->rewind();

lib/dml/pgsql_native_moodle_recordset.php

@@ -58,10 +58,6 @@ class pgsql_native_moodle_recordset extends moodle_recordset {
         $this->current = $this->fetch_next();
     }
 
-    public function rewind() {
-        // we can not seek, sorry - let's ignore it ;-)
-    }
-
     public function valid() {
         return !empty($this->current);
     }

user/index.php

@@ -531,16 +531,14 @@
     // of rows anyway. On a large course it will explode badly...
     //
     if ($mode===MODE_ENROLDETAILS) {
-        $userids = array();
-
-        foreach ($userlist as $user) {
-            $userids[] = $user->id;
+        if ($context->id != $frontpagectx->id) {
+            $userids = $DB->get_fieldset_sql("SELECT DISTINCT u.id $from $where $wheresearch $sort", $params,
+                                             $table->get_page_start(),  $table->get_page_size());
+        } else {
+            $userids = $DB->get_fieldset_sql("SELECT u.id $from $where $wheresearch $sort", $params,
+                                             $table->get_page_start(),  $table->get_page_size());
         }
         $userlist_extra = get_participants_extra($userids, $avoidroles, $course, $context);
-
-        // Only Oracle cannot seek backwards
-        // and must re-query...
-        $userlist->rewind();
     }
 
     if ($context->id == $frontpagectx->id) {