using Microsoft.EntityFrameworkCore;
public sealed class LabDb : DbContext
{
    public string TenantId { get; }
    public LabDb(DbContextOptions<LabDb> options, string tenantId) : base(options)
    { if (string.IsNullOrWhiteSpace(tenantId)) throw new System.ArgumentException("Trusted tenant required", nameof(tenantId)); TenantId = tenantId; }
    public DbSet<Item> Items => Set<Item>();
    protected override void OnModelCreating(ModelBuilder model)
    {
        model.Entity<Item>().HasQueryFilter("Tenant", x => x.TenantId == TenantId).HasQueryFilter("NotDeleted", x => !x.IsDeleted);
    }
}
public sealed class Item { public int Id { get; set; } public string Name { get; set; } = ""; public string TenantId { get; set; } = ""; public bool IsDeleted { get; set; } }