Fix backend validation

src/main/java/com/petshop/backend/config/DataInitializer.java

@@ -2,6 +2,7 @@ package com.petshop.backend.config;
 
 import com.petshop.backend.entity.User;
 import com.petshop.backend.repository.UserRepository;
+import com.petshop.backend.service.StoreAssignmentService;
 import com.petshop.backend.service.UserBusinessLinkageService;
 import org.springframework.boot.CommandLineRunner;
 import org.springframework.security.crypto.password.PasswordEncoder;
@@ -13,11 +14,13 @@ public class DataInitializer implements CommandLineRunner {
     private final UserRepository userRepository;
     private final PasswordEncoder passwordEncoder;
     private final UserBusinessLinkageService userBusinessLinkageService;
+    private final StoreAssignmentService storeAssignmentService;
 
-    public DataInitializer(UserRepository userRepository, PasswordEncoder passwordEncoder, UserBusinessLinkageService userBusinessLinkageService) {
+    public DataInitializer(UserRepository userRepository, PasswordEncoder passwordEncoder, UserBusinessLinkageService userBusinessLinkageService, StoreAssignmentService storeAssignmentService) {
         this.userRepository = userRepository;
         this.passwordEncoder = passwordEncoder;
         this.userBusinessLinkageService = userBusinessLinkageService;
+        this.storeAssignmentService = storeAssignmentService;
     }
 
     @Override
@@ -62,7 +65,7 @@ public class DataInitializer implements CommandLineRunner {
             }
         }
         // Ensure linked employee
-        userBusinessLinkageService.ensureLinkedEmployee(admin);
+        storeAssignmentService.assignStoreIfMissing(userBusinessLinkageService.ensureLinkedEmployee(admin), 1L);
 
         User staff = userRepository.findByUsername("staff").orElse(null);
         if (staff == null) {
@@ -102,7 +105,7 @@ public class DataInitializer implements CommandLineRunner {
             }
         }
         // Ensure linked employee
-        userBusinessLinkageService.ensureLinkedEmployee(staff);
+        storeAssignmentService.assignStoreIfMissing(userBusinessLinkageService.ensureLinkedEmployee(staff), 1L);
 
         User customer = userRepository.findByUsername("customer").orElse(null);
         if (customer == null) {

src/main/java/com/petshop/backend/controller/AuthController.java

@@ -17,6 +17,7 @@ import org.springframework.http.ResponseEntity;
 import org.springframework.security.authentication.AuthenticationManager;
 import org.springframework.security.authentication.BadCredentialsException;
 import org.springframework.security.authentication.DisabledException;
+import org.springframework.security.authentication.InternalAuthenticationServiceException;
 import org.springframework.security.authentication.UsernamePasswordAuthenticationToken;
 import org.springframework.security.core.Authentication;
 import org.springframework.security.core.context.SecurityContextHolder;
@@ -126,6 +127,13 @@ public class AuthController {
             Map<String, String> error = new HashMap<>();
             error.put("message", "Invalid username or password");
             return ResponseEntity.status(HttpStatus.UNAUTHORIZED).body(error);
+        } catch (InternalAuthenticationServiceException e) {
+            if (e.getCause() instanceof DisabledException disabledException) {
+                Map<String, String> error = new HashMap<>();
+                error.put("message", disabledException.getMessage());
+                return ResponseEntity.status(HttpStatus.FORBIDDEN).body(error);
+            }
+            throw e;
         } catch (DisabledException e) {
             Map<String, String> error = new HashMap<>();
             error.put("message", e.getMessage());

src/main/java/com/petshop/backend/exception/GlobalExceptionHandler.java

@@ -2,6 +2,7 @@ package com.petshop.backend.exception;
 
 import org.springframework.http.HttpStatus;
 import org.springframework.http.ResponseEntity;
+import org.springframework.dao.DataIntegrityViolationException;
 import org.springframework.validation.FieldError;
 import org.springframework.web.bind.MethodArgumentNotValidException;
 import org.springframework.web.bind.annotation.ExceptionHandler;
@@ -71,6 +72,16 @@ public class GlobalExceptionHandler {
         return ResponseEntity.status(HttpStatus.BAD_REQUEST).body(error);
     }
 
+    @ExceptionHandler(DataIntegrityViolationException.class)
+    public ResponseEntity<ErrorResponse> handleDataIntegrityViolationException(DataIntegrityViolationException ex) {
+        ErrorResponse error = new ErrorResponse(
+                HttpStatus.BAD_REQUEST.value(),
+                "Operation violates existing data relationships",
+                LocalDateTime.now()
+        );
+        return ResponseEntity.status(HttpStatus.BAD_REQUEST).body(error);
+    }
+
     @ExceptionHandler(Exception.class)
     public ResponseEntity<ErrorResponse> handleGenericException(Exception ex) {
         ErrorResponse error = new ErrorResponse(

src/main/java/com/petshop/backend/service/StoreAssignmentService.java

@@ -0,0 +1,34 @@
+package com.petshop.backend.service;
+
+import com.petshop.backend.entity.Employee;
+import com.petshop.backend.entity.EmployeeStore;
+import com.petshop.backend.entity.StoreLocation;
+import com.petshop.backend.exception.ResourceNotFoundException;
+import com.petshop.backend.repository.EmployeeStoreRepository;
+import com.petshop.backend.repository.StoreRepository;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+@Service
+public class StoreAssignmentService {
+
+    private final EmployeeStoreRepository employeeStoreRepository;
+    private final StoreRepository storeRepository;
+
+    public StoreAssignmentService(EmployeeStoreRepository employeeStoreRepository, StoreRepository storeRepository) {
+        this.employeeStoreRepository = employeeStoreRepository;
+        this.storeRepository = storeRepository;
+    }
+
+    @Transactional
+    public void assignStoreIfMissing(Employee employee, Long storeId) {
+        if (employeeStoreRepository.findByEmployeeEmployeeId(employee.getEmployeeId()).isPresent()) {
+            return;
+        }
+
+        StoreLocation store = storeRepository.findById(storeId)
+                .orElseThrow(() -> new ResourceNotFoundException("Store not found with id: " + storeId));
+
+        employeeStoreRepository.save(new EmployeeStore(employee, store));
+    }
+}