diff --git a/back_end/src/main/java/hackathon/FrisbYEE/rest/SessionResource.java b/back_end/src/main/java/hackathon/FrisbYEE/rest/SessionResource.java
index 183562d..e25b2d5 100644
--- a/back_end/src/main/java/hackathon/FrisbYEE/rest/SessionResource.java
+++ b/back_end/src/main/java/hackathon/FrisbYEE/rest/SessionResource.java
@@ -44,11 +44,11 @@ public class SessionResource {
     @PreAuthorize("hasRole('coach')")
     public ResponseEntity<?> create(@RequestBody SessionDTO dto) {
         try {
-            Session session = maptoEntity(dto);
-            if(sessionDAO.findById(session.getId()).isPresent()) {
-                return ResponseEntity.status(HttpStatus.OK).body("Session with ID " + session.getId() + " already exists.");
+            if(sessionDAO.findById(dto.getId()).isPresent()) {
+                return ResponseEntity.status(HttpStatus.OK).body("Session with ID " + dto.getId() + " already exists.");
 
             }
+            Session session = maptoEntity(dto);
             Coach c = coachDAO.findById(dto.getCoachId()).orElse(null);
             session.setCoach(c);
             sessionDAO.save(session);
@@ -161,7 +161,7 @@ public class SessionResource {
 
     private Session maptoEntity(SessionDTO dto) {
         Session session = new Session();
-        System.out.println("ID "+ dto.getId());
+        System.out.println("ID "+ session.getId());
         session.setName(dto.getName());
         session.setIsRecurrent(dto.getIsRecurrent());
         session.setCreneau(dto.getCreneau());
diff --git a/front_end/src/api.ts b/front_end/src/api.ts
index a7d0649..bd74948 100644
--- a/front_end/src/api.ts
+++ b/front_end/src/api.ts
@@ -45,7 +45,7 @@ export const athleteService = {
     delete: (id: number | string) => api.delete(`/athlete/${id}`),
 
     // session-related endpoints exposed by AthleteResource
-    getSessionsForAthlete: (athleteId: number | string) => api.get(`/athletes/athlete/${athleteId}/session`),
+    getSessionsForAthlete: (athleteId: number | null) => api.get(`/athletes/athlete/${athleteId}/session`),
     getAllSessions: () => api.get(`/athletes/session`),
     getActivitiesForSession: (sessionId: number | string) => api.get(`/athletes/session/${sessionId}/activities`),
     getSessionsAfterDate: (athleteId: number | string, date: string) => api.get(`/athletes/${athleteId}/session/after/${encodeURIComponent(date)}`),
@@ -84,7 +84,7 @@ export const coachService = {
     getByKeycloakId: (keycloakId: string) => api.get(`/coach/keycloak/${keycloakId}`),
     update: (id: number | string, data: any) => api.put(`/coach/update/${id}`, data),
     delete: (id: number | string) => api.delete(`/coach/delete/${id}`),
-    getSessionsForCoach: (coachId: number | string) => api.get(`/coach/${coachId}/session`),
+    getSessionsForCoach: (coachId: number | null) => api.get(`/coach/${coachId}/session`),
 };
 
 export const userService = {
diff --git a/front_end/src/classes.tsx b/front_end/src/classes.tsx
index 74ae159..b176e37 100644
--- a/front_end/src/classes.tsx
+++ b/front_end/src/classes.tsx
@@ -4,20 +4,21 @@ export type Groupe = "Entrainement" | "Competition" | "Loisir"| "";
 
 
 export class Ligne{
-    id!: number;
+    id: number|null = null;
     nom!: string;
     composition!: Athlete[] //les joueurs compososant la ligne
     tempsDeJeu!: number; // en minutes
 }
 
 export class User{
-    id!: number;
+    id: number|null = null;
     keycloakId!: string;
     nom!: string;
     prenom!:string;
     email!: string;
 }
 
+
 export class Admin extends User{
 
     constructor(dto:AdminDTO);
@@ -25,7 +26,7 @@ export class Admin extends User{
 
     constructor(dto?:AdminDTO){
         super();
-        this.id = dto?.id ?? 0;
+        this.id = dto?.id ?? null;
         this.keycloakId = dto?.id_keycloak ?? "";
         this.nom = dto?.name ?? "";
         this.prenom = dto?.prenom ?? "";
@@ -113,7 +114,7 @@ export class Coach extends User{
 }
 
 export class Session{
-    id!: number;
+    id: number|null = null;
     name!: string;
     activitesID: number[] = [];
     activites: Activite[] = [];
@@ -147,7 +148,7 @@ export class Session{
 
     toDTO():SessionDTO{
         const dto:SessionDTO = {
-            id: 0,
+            id: this.id,
             name: this.name,
             isRecurrent: this.isRecurrent,
             creneau: this.creneau.toISOString(),
@@ -162,7 +163,7 @@ export class Session{
 }
 
 export class Activite{
-    id!: number;
+    id: number|null = null;
     nom!: string;
     session!: Session;
     theme!: string;
@@ -184,7 +185,7 @@ export class Activite{
 
     toDTO():ActiviteDTO{
         const dto:ActiviteDTO = {
-            id: 0,
+            id: this.id,
             name: this.nom,
             duree: this.duree,
             dataActivite: [],
diff --git a/front_end/src/classesDTO.tsx b/front_end/src/classesDTO.tsx
index 5f7d466..cffde60 100644
--- a/front_end/src/classesDTO.tsx
+++ b/front_end/src/classesDTO.tsx
@@ -1,23 +1,23 @@
 import { Groupe } from "./classes";
 
 export type ActiviteDTO = {
-  id: number;
+  id: number|null;
   name: string;
   theme: string;
   duree: number;
   dataActivite: string[];
-  sessionId: number;
+  sessionId: number|null;
 }
 
 export type AdminDTO = {
-  id: number;
+  id: number|null;
   id_keycloak: string;
   name: string;
   prenom: string;
 }
 
 export type AthleteDTO = {
-  id:number;
+  id:number|null;
   id_keycloak: string;
   name: string;
   prenom: string;
@@ -28,7 +28,7 @@ export type AthleteDTO = {
 };
 
 export type CoachDTO = {
-  id: number;
+  id: number|null;
   id_keycloak: string;
   name: string;
   prenom: string;
@@ -36,14 +36,14 @@ export type CoachDTO = {
 };
 
 export type SessionDTO = {
-  id: number;
+  id: number|null;
   name: string;
   isRecurrent: boolean;
   creneau: string; // LocalDateTime → ISO string
   duree: number;
   groupe: Groupe;
 
-  coachId: number;
+  coachId: number|null;
   athleteIds: number[];
   activiteIds: number[];
 };
diff --git a/front_end/src/components/ressourceList.tsx b/front_end/src/components/ressourceList.tsx
index 27acfaa..a11730f 100644
--- a/front_end/src/components/ressourceList.tsx
+++ b/front_end/src/components/ressourceList.tsx
@@ -145,7 +145,7 @@ function LigneList({ lignes, tempsDeJeuParLigne }: LigneListProps) {
                     </div>
                     <div>
                         <strong>Temps de jeu total :</strong>{" "}
-                        {tempsDeJeuParLigne.get(lignes.id) ?? 0} min
+                        {/* {tempsDeJeuParLigne.get(lignes.id) ?? 0} min */}
                     </div>
                 </li>
             ))}
diff --git a/front_end/src/requetes.tsx b/front_end/src/requetes.tsx
index ff7a949..b5ff9c4 100644
--- a/front_end/src/requetes.tsx
+++ b/front_end/src/requetes.tsx
@@ -210,10 +210,14 @@ export async function getAllUserAPI(): Promise<User[]> {
     }
 }
 
-export async function getCoachByIdAPI(id:number): Promise<Coach|null> {
+export async function getCoachByIdAPI(id:number|null): Promise<Coach|null> {
     try{
-        const response = await coachService.getById(id);
-        return new Coach(response.data);
+        if(id!==null){
+            const response = await coachService.getById(id);
+            return new Coach(response.data);
+        }
+        console.error("Error fetching coach by id : id null");
+        return null;
     }catch (error) {
         console.error("Error fetching coach by id:", error);
         return null;