system-praktyk-api/src/InternshipSystem.Core/Entity/Company.cs

using System;
using System.Collections.Generic;
using FluentValidation;
using FluentValidation.Validators;

namespace InternshipSystem.Core
{
    public class Company
    {
        public long Id { get; set; }
        public string Nip { get; set; }
        public string Name { get; set; }
        public List<BranchOffice> Branches { get; set; }

        public long Provider { get; set; }

        public static Company CreateCompany(string nip, string name, long provider = 0) =>
            new Company
            {
                Nip = nip,
                Name = name,
                Provider = provider
            };

        public void AddBranchOffice(BranchOffice createBranch)
        {
            Branches.Add(createBranch);
        }

        public class Validator : AbstractValidator<Company>
        {
            public Validator()
            {
                RuleFor(x => x.Nip).NotNull();
                RuleFor(x => x.Name).NotNull();
            }
        }
    }
}