DomainService.cs

public class DomainService
{
    public class DenyOtherCompaniesProposals(Proposal proposal)
    {
        var proposalsToDeny = _repository.FindOpenForCandidate(proposal.CandidateId);
        foreach(var proposal in proposalsToDeny)
          proposal.Deny();
          
        _repository.Save(proposalsToDeny);
    }
}