diff --git a/src/main/java/fr/la_banquise/backend/data/model/Instance.java b/src/main/java/fr/la_banquise/backend/data/model/Instance.java
index 42da592..aab3b06 100644
--- a/src/main/java/fr/la_banquise/backend/data/model/Instance.java
+++ b/src/main/java/fr/la_banquise/backend/data/model/Instance.java
@@ -34,7 +34,7 @@ public class Instance {
     public User user;
 
     @ManyToOne
-    @JoinColumn(name = "practical_id")
+    @JoinColumn(name = "practical_id", nullable = false)
     public Tp tp;
 
     public Instance(String name, String ssh, String pwd, Long port, User user, Tp tp) {
diff --git a/src/main/java/fr/la_banquise/backend/data/model/Ji.java b/src/main/java/fr/la_banquise/backend/data/model/Ji.java
index 95d9151..987761b 100644
--- a/src/main/java/fr/la_banquise/backend/data/model/Ji.java
+++ b/src/main/java/fr/la_banquise/backend/data/model/Ji.java
@@ -10,6 +10,8 @@ import jakarta.persistence.Table;
 import lombok.AllArgsConstructor;
 import lombok.NoArgsConstructor;
 import java.util.List;
+import jakarta.persistence.ManyToOne;
+import jakarta.persistence.JoinColumn;
 
 @Entity
 @NoArgsConstructor
@@ -24,13 +26,16 @@ public class Ji {
     public String description;
     public String respo;
     public String date;
-    public Long   siteId;
 
-    public Ji(String name, String description, String respo, String date, Long siteId) {
+    @ManyToOne
+    @JoinColumn(name = "site_id")
+    public Site   site;
+
+    public Ji(String name, String description, String respo, String date, Site site) {
         this.name = name;
         this.description = description;
         this.respo = respo;
         this.date = date;
-        this.siteId = siteId;
+        this.site = site;
     }
 }
diff --git a/src/main/java/fr/la_banquise/backend/data/model/Site.java b/src/main/java/fr/la_banquise/backend/data/model/Site.java
index db3fc61..d832eef 100644
--- a/src/main/java/fr/la_banquise/backend/data/model/Site.java
+++ b/src/main/java/fr/la_banquise/backend/data/model/Site.java
@@ -14,6 +14,9 @@ import lombok.AllArgsConstructor;
 import lombok.NoArgsConstructor;
 import java.util.Set;
 import java.util.HashSet;
+import jakarta.persistence.OneToMany;
+import java.util.List;
+import java.util.ArrayList;
 
 @Entity
 @NoArgsConstructor
@@ -31,13 +34,15 @@ public class Site {
     public String name;
     public String description;
     public String address;
-    public Set<Long> jiInSite;
+
+    @OneToMany(mappedBy = "site")
+    public List<Ji> jiInSite;
 
     public Site(String name, String description, String address) {
         this.name = name;
         this.description = description;
         this.address = address;
-        this.jiInSite = new HashSet<Long>();
+        this.jiInSite = new ArrayList<Ji>();
     }
 
 
diff --git a/src/main/java/fr/la_banquise/backend/rest/JiResource.java b/src/main/java/fr/la_banquise/backend/rest/JiResource.java
index 13a409d..9c81679 100644
--- a/src/main/java/fr/la_banquise/backend/rest/JiResource.java
+++ b/src/main/java/fr/la_banquise/backend/rest/JiResource.java
@@ -73,7 +73,7 @@ public class JiResource {
 })
     public Response deleteJiByName(@QueryParam("name") String name) {
         try {
-            jiService.deleteJiByName(name);
+            jiService.deleteJi(name);
             return Response.ok().build();
         } catch (Exception e) {
             return Response.status(500).entity(Map.of("error", e.getMessage())).build();
diff --git a/src/main/java/fr/la_banquise/backend/services/JiService.java b/src/main/java/fr/la_banquise/backend/services/JiService.java
index 03b1e4c..a956d29 100644
--- a/src/main/java/fr/la_banquise/backend/services/JiService.java
+++ b/src/main/java/fr/la_banquise/backend/services/JiService.java
@@ -20,9 +20,9 @@ public class JiService {
     @Transactional
     public Ji createJi(String name, String description, String address, String respo, String site_name) {
         Site site = siteService.getSiteByName(site_name);
-        Ji ji = new Ji(name, description, address, respo, site.id);
+        Ji ji = new Ji(name, description, address, respo, site);
         jiRepository.persist(ji);
-        siteService.addJi(site, ji.id);
+        siteService.addJi(site, ji);
         return ji;
     }
 
@@ -45,15 +45,16 @@ public class JiService {
     }
 
     @Transactional
-    public void deleteJiById(Long id) {
-        siteService.removeJi(siteService.getSiteById(getJiById(id).siteId), id);
+    public void deleteJi(Long id) {
+        Ji ji = getJiById(id);
+        siteService.removeJi(ji.site, ji);
         jiRepository.deleteById(id);
     }
 
     @Transactional
-    public void deleteJiByName(String name) {
+    public void deleteJi(String name) {
         Ji ji = getJiByName(name);
-        siteService.removeJi(siteService.getSiteById(ji.siteId), ji.id);
+        siteService.removeJi(ji.site, ji);
         jiRepository.delete(ji);
     }
 }
diff --git a/src/main/java/fr/la_banquise/backend/services/SiteService.java b/src/main/java/fr/la_banquise/backend/services/SiteService.java
index 2ea1743..0086770 100644
--- a/src/main/java/fr/la_banquise/backend/services/SiteService.java
+++ b/src/main/java/fr/la_banquise/backend/services/SiteService.java
@@ -1,6 +1,7 @@
 package fr.la_banquise.backend.services;
 
 import fr.la_banquise.backend.data.model.Site;
+import fr.la_banquise.backend.data.model.Ji;
 import fr.la_banquise.backend.data.repository.SiteRepository;
 import jakarta.enterprise.context.ApplicationScoped;
 import jakarta.inject.Inject;
@@ -39,13 +40,13 @@ public class SiteService {
     }
 
     @Transactional
-    public void addJi(Site site, Long id){
-        site.jiInSite.add(id);
+    public void addJi(Site site, Ji ji){
+        site.jiInSite.add(ji);
     }
 
     @Transactional
-    public void removeJi(Site site, Long id){
-        site.jiInSite.remove(id);
+    public void removeJi(Site site, Ji ji){
+        site.jiInSite.remove(ji);
     }
 
     @Transactional