try

Webshop.Domain/Entities/ApplicationUser.cs

@@ -1,13 +0,0 @@
-using Microsoft.AspNetCore.Identity;
-using System;
-using System.Collections.Generic;
-
-namespace Webshop.Domain.Entities
-{
-    public class ApplicationUser : IdentityUser
-    {
-        public DateTimeOffset CreatedDate { get; set; }
-        public DateTimeOffset? LastActive { get; set; }
-        public virtual Customer Customer { get; set; }
-    }
-}

Webshop.Domain/Entities/Customer.cs

@@ -1,25 +1,40 @@
-using System;
-
+// src/Webshop.Domain/Entities/Customer.cs
+using System;
 using System.ComponentModel.DataAnnotations;
+using System.Collections.Generic;
+using Webshop.Domain.Identity; // Für ApplicationUser
 
 namespace Webshop.Domain.Entities
 {
     public class Customer
     {
         [Key]
-        public Guid Id { get; set; }
-        [Required]
-        public string AspNetUserId { get; set; }
-        [Required]
-        [MaxLength(100)]
-        public string FirstName { get; set; }
-        [Required]
-        [MaxLength(100)]
-        public string LastName { get; set; }
+        public Guid Id { get; set; } = Guid.NewGuid(); // Default-Wert setzen
 
-        public virtual ApplicationUser User { get; set; }
+        [Required]
+        public string AspNetUserId { get; set; } // Fremdschlüssel zu ApplicationUser.Id
+
+        [Required]
+        [MaxLength(100)]
+        public string FirstName { get; set; } = string.Empty;
+
+        [Required]
+        [MaxLength(100)]
+        public string LastName { get; set; } = string.Empty;
+
+        // << ENTFERNT: Email ist auf ApplicationUser >>
+        // << ENTFERNT: PhoneNumber ist auf ApplicationUser >>
+        // << ENTFERNT: CreatedDate ist auf ApplicationUser >>
+
+        public Guid? DefaultShippingAddressId { get; set; } // Fremdschlüssel zur Standardversandadresse
+        public Guid? DefaultBillingAddressId { get; set; } // Fremdschlüssel zur Standardrechnungsadresse
+
+        // Navigation Property zum ApplicationUser
+        public virtual ApplicationUser User { get; set; } = default!; // Muss auf ApplicationUser verweisen
+
+        // Navigation Properties zu Collections
         public virtual ICollection<Address> Addresses { get; set; } = new List<Address>();
         public virtual ICollection<Order> Orders { get; set; } = new List<Order>();
         public virtual ICollection<Review> Reviews { get; set; } = new List<Review>();
     }
-}
+}

Webshop.Domain/Identity/ApplicationUser.cs

@@ -0,0 +1,16 @@
+// src/Webshop.Domain/Identity/ApplicationUser.cs
+using Microsoft.AspNetCore.Identity;
+using System;
+
+namespace Webshop.Domain.Identity // KORREKTER NAMESPACE
+{
+    public class ApplicationUser : IdentityUser
+    {
+        public DateTimeOffset CreatedDate { get; set; } = DateTimeOffset.UtcNow; // Setzt Standardwert
+        public DateTimeOffset? LastActive { get; set; }
+
+        // Navigation Property zur Customer-Entität (One-to-One)
+        // Customer ist nullable, falls nicht jeder ApplicationUser ein Customer-Profil hat
+        public virtual Entities.Customer? Customer { get; set; }
+    }
+}

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 >>
     }
 }