diff --git a/public/main/inc/lib/sessionmanager.lib.php b/public/main/inc/lib/sessionmanager.lib.php
index 851c384018..17e4f3ffd1 100644
--- a/public/main/inc/lib/sessionmanager.lib.php
+++ b/public/main/inc/lib/sessionmanager.lib.php
@@ -5558,13 +5558,10 @@ class SessionManager
                                 }
                             }
 
-                            $userList[] = $user_id;
-                            // Insert new users.
-                            $sql = "INSERT IGNORE INTO $tbl_session_user SET
-                                    user_id = '$user_id',
-                                    session_id = '$session_id',
-                                    registered_at = '".api_get_utc_datetime()."'";
-                            Database::query($sql);
+                            $userEntity = api_get_user_entity($user_id);
+                            $sessionEntity = api_get_session_entity($session_id);
+                            $sessionEntity->addUserInSession(Session::STUDENT, $userEntity);
+
                             if ($debug) {
                                 $logger->debug("Adding User #$user_id ($user) to session #$session_id");
                             }
diff --git a/src/CoreBundle/Entity/Session.php b/src/CoreBundle/Entity/Session.php
index 0bda39bde5..d190a2ad86 100644
--- a/src/CoreBundle/Entity/Session.php
+++ b/src/CoreBundle/Entity/Session.php
@@ -260,7 +260,7 @@ class Session implements ResourceWithAccessUrlInterface, Stringable
         'session:write',
     ])]
     #[ORM\Column(name: 'show_description', type: 'boolean', nullable: true)]
-    protected ?bool $showDescription;
+    protected ?bool $showDescription = false;
 
     #[Groups(['session:read', 'session:write', 'user_subscriptions:sessions'])]
     #[ORM\Column(name: 'duration', type: 'integer', nullable: true)]
@@ -446,7 +446,7 @@ class Session implements ResourceWithAccessUrlInterface, Stringable
 
     public function getShowDescription(): bool
     {
-        return $this->showDescription;
+        return $this->showDescription ?? false;
     }
 
     public function setShowDescription(bool $showDescription): self
@@ -810,7 +810,18 @@ class Session implements ResourceWithAccessUrlInterface, Stringable
 
     public function addUserInSession(int $relationType, User $user): self
     {
-        $sessionRelUser = (new SessionRelUser())->setUser($user)->setRelationType($relationType);
+        foreach ($this->getUsers() as $existingSubscription) {
+            if (
+                $existingSubscription->getUser()->getId() === $user->getId() &&
+                $existingSubscription->getRelationType() === $relationType
+            ) {
+                return $this;
+            }
+        }
+
+        $sessionRelUser = (new SessionRelUser())
+            ->setUser($user)
+            ->setRelationType($relationType);
         $this->addUserSubscription($sessionRelUser);
 
         return $this;
@@ -985,8 +996,12 @@ class Session implements ResourceWithAccessUrlInterface, Stringable
      * If user status in session is student, then increase number of course users.
      * Status example: Session::STUDENT.
      */
-    public function addUserInCourse(int $status, User $user, Course $course): SessionRelCourseRelUser
+    public function addUserInCourse(int $status, User $user, Course $course): ?SessionRelCourseRelUser
     {
+        if ($this->hasUserInCourse($user, $course, $status)) {
+            return null;
+        }
+
         $userRelCourseRelSession = (new SessionRelCourseRelUser())
             ->setCourse($course)
             ->setUser($user)
@@ -998,7 +1013,9 @@ class Session implements ResourceWithAccessUrlInterface, Stringable
 
         if (self::STUDENT === $status) {
             $sessionCourse = $this->getCourseSubscription($course);
-            $sessionCourse->setNbrUsers($sessionCourse->getNbrUsers() + 1);
+            if ($sessionCourse) {
+                $sessionCourse->setNbrUsers($sessionCourse->getNbrUsers() + 1);
+            }
         }
 
         return $userRelCourseRelSession;