try

Webshop.Domain/Interfaces/ICustomerRepository.cs

@@ -1,4 +1,5 @@
-using System;
+// src/Webshop.Domain/Interfaces/ICustomerRepository.cs
+using System.Collections.Generic;
 using System.Threading.Tasks;
 using Webshop.Domain.Entities;
 
@@ -6,7 +7,12 @@ namespace Webshop.Domain.Interfaces
 {
     public interface ICustomerRepository
     {
-        Task<Customer?> GetByUserIdAsync(string userId);
-        Task UpdateAsync(Customer customer);
+        Task<IEnumerable<Customer>> GetAllAsync(); // Standard CRUD
+        Task<Customer?> GetByIdAsync(Guid id); // Standard CRUD
+        Task AddAsync(Customer entity); // Standard CRUD
+        Task UpdateAsync(Customer entity); // Standard CRUD
+        Task DeleteAsync(Guid id); // Standard CRUD
+
+        Task<Customer?> GetByUserIdAsync(string userId); // << DIESE METHODE IST NEU UND WICHTIG >>
     }
 }