C++ database

// Database.cpp
#include <iostream>
#include <stdexcept>
#include "Database.h"

using namespace std;
namespace Records
{
    Employee& Database::addEmployee(const string &firstName,
                                    const string &lastName)
    {
        Employee theEmployee{firstName, lastName};
        theEmployee.setEmployeeNumber(m_nextEmployeeNumber++);
        theEmployee.hire();
        m_employees.push_back(theEmployee);
        return m_employees.back();
    }

    Employee& Database::getEmployee(int employeeNumber)
    {
        for (auto &employee : m_employees)
        {
            if (employee.getEmployeeNumber() == employeeNumber)
            {
                return employee;
            }
        }
        throw logic_error{"No employee found."};
    }
    Employee& Database::getEmployee(const std::string& firstName, const std::string& lastName)
    {
        for (auto& employee : m_employees)
        {
            if (employee.getFirstName() == firstName && employee.getLastName() == lastName)
            {
                return employee;
            }
        }
        throw logic_error{ "No employee found." };
    }

    void Database::displayAll() const
    {
        for (const auto& employee : m_employees) { employee.display(); }
    }

    void Database::displayCurrent() const
    {
        for (const auto& employee : m_employees) {
            if (employee.isHired()) { employee.display(); }
        }
    }
    void Database::displayFormer() const
    {
        for (const auto& employee : m_employees) {
            if (!employee.isHired()) { employee.display(); }
        }
    }
}