Update the repositories to solve the N+1 problem.

src/main/java/space/kklochko/jpa_hospital_example/db/repositories/AbstractRepository.java

@@ -3,7 +3,7 @@ package space.kklochko.jpa_hospital_example.db.repositories;
 import jakarta.persistence.EntityManager;
 import lombok.Setter;
 
-import java.util.ArrayList;
+import java.util.List;
 import java.util.UUID;
 
 @Setter
@@ -18,7 +18,7 @@ public abstract class AbstractRepository<T> {
 
     public abstract T read(UUID id);
 
-    public abstract ArrayList<T> readAll();
+    public abstract List<T> readAll();
 
     public abstract boolean update(T object);
 

src/main/java/space/kklochko/jpa_hospital_example/db/repositories/DepartmentRepository.java

@@ -1,13 +1,15 @@
 package space.kklochko.jpa_hospital_example.db.repositories;
 
+import jakarta.persistence.EntityGraph;
 import jakarta.persistence.EntityManager;
 import jakarta.persistence.TypedQuery;
 import space.kklochko.jpa_hospital_example.db.repositories.blocks.TransactionalInsert;
 import space.kklochko.jpa_hospital_example.db.repositories.blocks.TransactionalRemove;
 import space.kklochko.jpa_hospital_example.db.repositories.blocks.TransactionalUpdate;
 import space.kklochko.jpa_hospital_example.models.Department;
+import space.kklochko.jpa_hospital_example.models.Patient;
 
-import java.util.ArrayList;
+import java.util.List;
 import java.util.UUID;
 
 public class DepartmentRepository extends AbstractRepository<Department> {
@@ -25,10 +27,28 @@ public class DepartmentRepository extends AbstractRepository<Department> {
         return manager.find(Department.class, id);
     }
 
-    public ArrayList<Department> readAll() {
+    public List<Department> readAll() {
+        EntityGraph<Department> entityGraph = manager.createEntityGraph(Department.class);
+        entityGraph.addAttributeNodes("patients");
+        //entityGraph.addSubgraph("patients")
+                   //.addAttributeNodes("indicators");
+
         TypedQuery<Department> query = manager.createQuery("SELECT d FROM Department d", Department.class);
+        query.setHint( "javax.persistence.fetchgraph", entityGraph);
+
+        List<Department> departments = query.getResultList();
+
+        for(Department department : departments) {
+            EntityGraph<Patient> patientEntityGraph = manager.createEntityGraph(Patient.class);
+            patientEntityGraph.addAttributeNodes("indicators");
+
+            TypedQuery<Patient> patientQuery = manager.createQuery("SELECT p FROM Patient p", Patient.class);
+            patientQuery.setHint( "javax.persistence.fetchgraph", patientEntityGraph);
+
+            department.setPatients(patientQuery.getResultList());
+        }
 
-        return (ArrayList<Department>) query.getResultList();
+        return departments;
     }
 
     public boolean update(Department object) {

src/main/java/space/kklochko/jpa_hospital_example/db/repositories/IndicatorRepository.java

@@ -7,7 +7,7 @@ import space.kklochko.jpa_hospital_example.db.repositories.blocks.TransactionalR
 import space.kklochko.jpa_hospital_example.db.repositories.blocks.TransactionalUpdate;
 import space.kklochko.jpa_hospital_example.models.Indicator;
 
-import java.util.ArrayList;
+import java.util.List;
 import java.util.UUID;
 
 public class IndicatorRepository extends AbstractRepository<Indicator> {
@@ -25,10 +25,10 @@ public class IndicatorRepository extends AbstractRepository<Indicator> {
         return manager.find(Indicator.class, id);
     }
 
-    public ArrayList<Indicator> readAll() {
+    public List<Indicator> readAll() {
         TypedQuery<Indicator> query = manager.createQuery("SELECT i FROM Indicator i", Indicator.class);
 
-        return (ArrayList<Indicator>) query.getResultList();
+        return query.getResultList();
     }
 
     public boolean update(Indicator object) {

src/main/java/space/kklochko/jpa_hospital_example/db/repositories/PatientRepository.java

@@ -1,5 +1,6 @@
 package space.kklochko.jpa_hospital_example.db.repositories;
 
+import jakarta.persistence.EntityGraph;
 import jakarta.persistence.EntityManager;
 import jakarta.persistence.TypedQuery;
 import space.kklochko.jpa_hospital_example.db.repositories.blocks.TransactionalInsert;
@@ -7,7 +8,7 @@ import space.kklochko.jpa_hospital_example.db.repositories.blocks.TransactionalR
 import space.kklochko.jpa_hospital_example.db.repositories.blocks.TransactionalUpdate;
 import space.kklochko.jpa_hospital_example.models.Patient;
 
-import java.util.ArrayList;
+import java.util.List;
 import java.util.UUID;
 
 public class PatientRepository extends AbstractRepository<Patient> {
@@ -25,10 +26,14 @@ public class PatientRepository extends AbstractRepository<Patient> {
         return manager.find(Patient.class, id);
     }
 
-    public ArrayList<Patient> readAll() {
+    public List<Patient> readAll() {
+        EntityGraph<Patient> entityGraph = manager.createEntityGraph(Patient.class);
+        entityGraph.addAttributeNodes("indicators");
+
         TypedQuery<Patient> query = manager.createQuery("SELECT p FROM Patient p", Patient.class);
+        query.setHint( "javax.persistence.fetchgraph", entityGraph);
 
-        return (ArrayList<Patient>) query.getResultList();
+        return query.getResultList();
     }
 
     public boolean update(Patient object) {