c# - 2つのクラスからデータを取得するDataReaderの問題

Question

私は SQL に非常に不慣れで、1 回しかレッスンを受けていません。DataReader を使用して 2 つのクラスから情報を取得する方法を理解しようとしています。

私の顧客クラス:

public class Customer
{
    private CreditCard _creditCard;
    private List<Subscription> _subscriptions;
    private int _customerId;
    private string _name;
    private string _address;
    private int _zipCode;
    private string _city;
    private string _email;
    private string _password;


    public Customer(int id, string name, string email, string password)
    {
        this._customerId = id;
        this._name = name;
        this._email = email;
        this._password = password;
        this._subscriptions = new List<Subscription>();
    }

    public Customer(int id, string name)
    {
        this._customerId = id;
        this._name = name;
        _subscriptions = new List<Subscription>();
    }

    public override string ToString()
    {
        return _customerId + " " + _name;
    }

    public int CustomerId
    {
        get { return _customerId; }
        set { _customerId = value; }
    }

    public string Name
    {
        get { return _name; }
        set { _name = value; }
    }

    public string Address
    {
        get { return _address; }
        set { _address = value; }
    }

    public int ZipCode
    {
        get { return _zipCode; }
        set { _zipCode = value; }
    }

    public string City
    {
        get { return _city; }
        set { _city = value; }
    }

    public string Email
    {
        get { return _email; }
        set { _email = value; }
    }

    public string Password
    {
        get { return _password; }
        set { _password = value; }
    }



    public List<Subscription> Subscriptions
    {
        get { return _subscriptions; }
    }

    public void AddSubscription(Subscription s)
    {
        _subscriptions.Add(s);
    }

    public Subscription FindSubscription(int sId)
    {
        bool found = false;
        int i = 0;
        while (!found && i < _subscriptions.Count)
        {
            if (_subscriptions[i].SubscriptionId == sId)
                found = true;
            else
                i++;
        }
        if (found)
            return _subscriptions[i];
        else
            return new Subscription();
    }

}

私の購読クラス:

public class Subscription
{
    private SubscriptionType _subscriptionType;
    private CarModel _carModel;
    private List<Booking> _bookings;
    private int _subscriptionId;

    public Subscription(int subscriptionId, SubscriptionType subscriptionType, CarModel carModel)
    {
        this._subscriptionId = subscriptionId;
        this._subscriptionType = subscriptionType;
        this._carModel = carModel;
        _bookings = new List<Booking>();
    }

    public Subscription()
    { }

    public int SubscriptionId
    {
        get { return _subscriptionId; }
        set { _subscriptionId = value; }
    }

    public SubscriptionType SubscriptionType
    {
        get { return _subscriptionType; }
    }

    public CarModel CarModel
    {
        get { return _carModel; }
    }

    public override string ToString()
    {
        return this.SubscriptionId + "\t " + this.SubscriptionType + "\t " + this.CarModel;
    }
}

私のデータベースクラス:

public class DBCustomer
{
    private static SqlCommand dbCmd = null;

    public static List<Customer> GetCustomers()
    {
        List<Customer> returnList = new List<Customer>();
        string sql = "select * from Customer";
        dbCmd = AccessDBSQLClient.GetDbCommand(sql);

        IDataReader dbReader;
        dbReader = dbCmd.ExecuteReader();

        Customer c;

        while (dbReader.Read())
        {
            c = new Customer(Convert.ToInt32(dbReader["cId"].ToString()), dbReader["cName"].ToString());
            returnList.Add(c);
        }
        AccessDBSQLClient.Close();
        return returnList;

    }

    public static List<Customer> GetCustomersByEmail(string email)
    {
        List<Customer> returnList = new List<Customer>();
        string sql = "select * from Customer where cEmail = '" + email+"'";
        dbCmd = AccessDBSQLClient.GetDbCommand(sql);

        IDataReader dbReader;
        dbReader = dbCmd.ExecuteReader();

        Customer c;

        while (dbReader.Read())
        {
            c = new Customer(Convert.ToInt32(dbReader["cId"].ToString()), dbReader["cName"].ToString());
            returnList.Add(c);
        }
        AccessDBSQLClient.Close();
        return returnList;

    }

    public static List<Subscription> GetCustomerSubscriptions(int cId)
    {
        List<Subscription> returnList = new List<Subscription>();
        string sql = "select S.sId, ST.stName,CM.cmDescription "
                   + "from Customer C, Subscription S, SubscriptionType ST, CarModel CM "
                   + "where C.cId = S.cId "
                   + "and S.stId = ST.stId "
                   + "and S.cmId = CM.cmId "
                   + "and C.cId = " + cId;
        dbCmd = AccessDBSQLClient.GetDbCommand(sql);

        IDataReader dbReader;
        dbReader = dbCmd.ExecuteReader();

        Subscription s;

        while (dbReader.Read())
        {
            //s = new Subscription();
            s = new Subscription((int)(dbReader["sId"]).ToString(),
                    dbReader["stName"],
                    dbReader["cmDescription"]);
            returnList.Add(s);
        }
        AccessDBSQLClient.Close();
        return returnList;

    }

明らかに、GetCustomers メソッドと GetCustomersByEmail メソッドは機能していますが、GetCustomerSubscriptions メソッドを作成する方法がわかりません。これは、2 つのクラスからデータを返す必要があり、Customer を作成して結果セットに追加することはできません。