(B) Validate duplicate serial number in create employee method

Clinics.Backend/Application/Employees/Commands/Create/CreateEmployeeCommandHandler.cs

 using Application.Abstractions.CQRS.Commands;
 using Domain.Entities.People.Employees;
+using Domain.Errors;
 using Domain.Repositories;
 using Domain.Shared;
 using Domain.UnitOfWork;
@@ -33,6 +34,14 @@ public class CreateEmployeeCommandHandler : ICommandHandler<CreateEmployeeComman
         if (employeeResult.IsFailure)
             return Result.Failure(employeeResult.Error);
 
+
+        #region Check existed serial number
+        Result<Employee> existedResult = await _employeesRepository.GetEmployeeBySerialNumberAsync(request.SerialNumber);
+        if (existedResult.IsSuccess)
+            return Result.Failure(DomainErrors.EmployeeAlreadyExist);
+        #endregion
+
+
         try
         {
             _employeesRepository.Create(employeeResult.Value);

Clinics.Backend/Domain/Errors/DomainErrors.cs

@@ -25,6 +25,9 @@ public static class DomainErrors
     public static Error PhoneAlreadyExist =>
         new("Domain.PhoneAlreadyExist", "رقم الهاتف موجود بالفعل");
 
+    public static Error EmployeeAlreadyExist =>
+        new("Domain.EmployeeAlreadyExist", "الموظف موجود بالفعل");
+
     public static Error VisitAlreadyHasThisMedicine =>
         new("Domain.VisitAlreadyHasThisMedicine", "تحتوي الوصفة الطبية بالفعل على الدواء الذي تحاول اضافته");
 
@@ -32,6 +35,6 @@ public static class DomainErrors
         new("Domain.VisitAlreadyHasThisMedicalTest", "تحتوي هذه الزيارة بالفعل على التحليل الطبي الذي تحاول اضافته");
 
     public static Error VisitAlreadyHasThisMedicalImage =>
-    new("Domain.PatientAlreadyHasThisMedicine", "تحتوي هذه الزيارة بالفعل على الصورة التي تحاول اضافتها");
+        new("Domain.PatientAlreadyHasThisMedicine", "تحتوي هذه الزيارة بالفعل على الصورة التي تحاول اضافتها");
 
 }

Clinics.Backend/Domain/Errors/PersistenceErrors.cs

@@ -6,4 +6,7 @@ public static class PersistenceErrors
 {
     public static Error UnableToCompleteTransaction =>
         new("Persistence.UnableToCompleteTransaction", "حدثت مشكلة عند الاتصال مع قاعدة البيانات");
+
+    public static Error NotFound =>
+        new("Persistence.NotFound", "الغرض المطلوب غير موجود");
 }

Clinics.Backend/Domain/Repositories/IEmployeesRepository.cs

 using Domain.Entities.People.Employees;
 using Domain.Repositories.Base;
+using Domain.Shared;
 
 namespace Domain.Repositories;
 
 public interface IEmployeesRepository : IRepository<Employee>
 {
+    #region Get by serial number
+    public Task<Result<Employee>> GetEmployeeBySerialNumberAsync(string serialNumber);
+
+    #endregion
 }

Clinics.Backend/Persistence/Repositories/EmployeesRepository.cs

 using Domain.Entities.People.Employees;
+using Domain.Errors;
 using Domain.Repositories;
+using Domain.Shared;
 using Microsoft.EntityFrameworkCore;
 using Persistence.Context;
 using Persistence.Repositories.Base;
@@ -18,4 +20,14 @@ public class EmployeesRepository : Repositroy<Employee>, IEmployeesRepository
 
     }
     #endregion
+
+    #region Get by serial Number
+    public async Task<Result<Employee>> GetEmployeeBySerialNumberAsync (string serialNumber)
+    {
+        var all = await _context.Set<Employee>().Where(employee => employee.SerialNumber == serialNumber).ToListAsync();
+        if (all.Count != 1)
+            return Result.Failure<Employee>(PersistenceErrors.NotFound);
+        return Result.Success<Employee>(all.First());
+    }
+    #endregion
 }