DAO实现:使DAO对象成为其他DAO的属性

Question

如何使DAO对象成为其他DAO的属性？

假设我有一个带有Department属性的Employee对象

public class Employee {
     public Department;

      //setter and getters
  }

我有这个EmployeeDAO和DepartmentDAO接口以及相应的实现

我有DAOFactory

public abstract class DAOFactory {

// db connection instantiation here

public IEmployeeDAO getEmployeeDAO() {
    return new EmployeeDAOImpl(this);
}

public IDepartmentDAO getDepartmentDAO() {
    return new DepartmentDAOImpl(this);
}

}

我有一个servlet来实例化这个DAOfactory

public class EmployeeController extends HttpServlet {

public EmployeeController() {
    super();
    DBUtils dbInstance = DBUtils.getInstance("mysql");
    System.out.println("DAOFactory successfully obtained: " + dbInstance);

    // Obtain UserDAO.
    employeeDAO = dbInstance.getEmployeeDAO();
    departmentDAO = dbInstance.getDepartmentDAO();
    jobDAO = dbInstance.getJobDAO();

}
protected void doGet(HttpServletRequest request,
        HttpServletResponse response) throws ServletException, IOException {

            employees = employeeDAO.findAll();

            request.setAttribute("employees", employees);

}

我的问题是，当我调用employeeDAO的findAll方法时，如何映射employeeDAO内部的Department或它的实现？

在我试图绘制结果的过程中，我遇到了这样的情况：

    private  Employee map(ResultSet rs) throws SQLException {
    Employee employee = new Employee();

    employee.setEmployeeID(rs.getInt("EMPLOYEE_ID"));
    employee.setFirstName(rs.getString("FIRST_NAME"));
    employee.setLastName(rs.getString("LAST_NAME"));

    Department department = new DepartmentDAOImpl().getDepartmentByID(rs
            .getInt("DEPARTMENT_ID"));

    employee.setDepartment(department);

    return employee;
}

但我认为这是一个错误的方法。有人能帮我吗？

Answer 1

您的EmployeeDAOImpl依赖于IDepartmentDAO。与其直接实例化EmployeeDAOImpl，不如将其声明为依赖项，并让构造该的代码知道如何解决该问题。

假设

interface IEmployeeDAO {
    Employee load(long id);
}
interface IDepartmentDAO  {
    Department load(long id);
}

由于接口需要构造函数中所需的dao

class EmployeeDAOImpl implements IEmployeeDAO {

    private final DAOFactory factory;
    private final IDepartmentDAO departmentDAO;

    public EmployeeDAOImpl(DAOFactory factory, IDepartmentDAO departmentDAO) {
        this.factory = factory;
        this.departmentDAO = departmentDAO;
    }
    ...

现在你可以在任何地方使用它了。例如：

@Override
public Employee load(long id) {
    ...
    long departmentId = ....
    Department department = departmentDAO.load(departmentId);
    employee.department = department;
    return employee;
}

知道使用哪种实现的DAOFactory现在可以通过添加一个简单的参数来提供依赖关系。

public IEmployeeDAO getEmployeeDAO() {
    return new EmployeeDAOImpl(this, getDepartmentDAO());
}