Core_Be/Models/TenantCustomerLink.cs

using System.ComponentModel.DataAnnotations;

namespace Fitness_core_BE.Models
{
    // Tenant-DB only, one row per customer this gym has ever enrolled. Every tenant-local
    // table that used to FK straight to the central Customer.CusId keeps doing so, unchanged
    // -- TenantCustomerLinkId IS the central Customer.CusId (same GUID value), not a new
    // surrogate key. That's deliberate: a fresh surrogate key would mean "customerId" holds
    // a different value depending on whether it's about to query a central or a tenant table,
    // which is exactly the kind of silent, hard-to-spot bug this split needs to avoid. EF/MySQL
    // still can't enforce this as a real cross-schema FK constraint -- it's just data -- but the
    // ID space stays uniform everywhere, and this row is also the local anchor tenant tables
    // join against for cached display fields without a central round-trip.
    public class TenantCustomerLink
    {
        [Key]
        public Guid TenantCustomerLinkId { get; set; } // == central Customer.CusId

        // = the shared login User id (same GUID in Auth's Users table), cached.
        public Guid CentralUserId { get; set; }

        public string? DisplayName { get; set; }
        public string? PrimaryPhoneCached { get; set; }
        public string? EmailCached { get; set; }

        // What a client-initiated delete flips. Central Customer.IsActive is never touched
        // by a client-initiated delete -- see CustomerRepository.DeactivateCustomerForClient.
        public bool IsActiveAtThisClient { get; set; } = true;

        public DateTime CreatedAt { get; set; } = DateTime.UtcNow;
        public DateTime UpdatedAt { get; set; } = DateTime.UtcNow;
    }
}