根据我从数据库中获得的另一个类属性将数据提供给一个类属性答案

【问题标题】：Giving data to a class property according to another classes property which I get from the database根据我从数据库中获得的另一个类属性将数据提供给一个类属性
【发布时间】：2013-06-19 08:55:57
【问题描述】：

我正在从数据库的两个表中获取数据。

表 1 - 成员：

        public List<Member> ListMembers()
        {
            List<Member> Members = new List<Member>();

            string SELECT = "SELECT * FROM Members ORDER BY Id";

            using (sqlConnection = new SqlConnection(sqlConnectionString_WORK))
            {
                sqlConnection.Open();

                using (SqlCommand sqlCommand = new SqlCommand(SELECT, sqlConnection))
                {
                    var sqlReader = sqlCommand.ExecuteReader();

                    while (sqlReader.Read())
                    {
                        var member = new Member
                        {
                            Id = Convert.ToInt32(sqlReader["Id"]),
                            Name = sqlReader["Name"].ToString(),
                            Surname = sqlReader["Surname"].ToString(),
                            EntryDate = Convert.ToDateTime(sqlReader["EntryDate"])
                        };

                        if (member.EntryDate < DateTime.Today)
                        {
                            member.Status = Status.Unpaid.ToString();
                        }

                        else
                        {
                            member.Status = Status.Paid.ToString();
                        }

                        Members.Add(member);
                    }
                }
            }

            return Members;
        }

表 2 - 付款：

        public List<Payment> ListPayments(Payment entity)
        {
            List<Payment> Payments = new List<Payment>();

            string SELECT = "SELECT * FROM Payments WHERE Id = @Id";

            using (sqlConnection = new SqlConnection(sqlConnectionString_WORK))
            {
                sqlConnection.Open();

                using (SqlCommand sqlCommand = new SqlCommand(SELECT, sqlConnection))
                {
                    sqlCommand.Parameters.Add("@Id", SqlDbType.Int).Value = entity.Id;

                    var sqlReader = sqlCommand.ExecuteReader();

                    while (sqlReader.Read())
                    {
                        var payment = new Payment
                        {
                            Id = Convert.ToInt32(sqlReader["Id"]),
                            Amount = Convert.ToDecimal(sqlReader["Amount"]),
                            StartDay = Convert.ToDateTime(sqlReader["StartDay"]),
                            EndDay = Convert.ToDateTime(sqlReader["EndDay"])
                        };

                        Payments.Add(payment);
                    }
                }
            }

            return Payments;
        }

付款的 ID 等于特定会员的 ID。（如果会员 ID 为 100，则他/她的所有付款都将具有相同的 ID 100）。

现在...在 ListMembers() 中，我根据他们的 EntryDate 给状态“已付款”和“未付款”，但我想根据他们的 LAST Payment 给他们状态。所以，而不是：

if (member.EntryDate < DateTime.Today)
{
     member.Status = Status.Unpaid.ToString();
}

应该是：

if (lastPayment < DateTime.Today) // lastPayment is just a word I'm using, It's not declared anywhere, I don't know how to get that value.
{
     member.Status = Status.Unpaid.ToString();
}

我真的迷路了，有人可以帮助我吗？我不知道该怎么办。

【问题讨论】：

“lastPayment”会是最近EndDay 的那个吗？
@ColmPrunty 是的。所以实际上它会是“if(theLastEndDay
你搞定了吗？

标签： c# winforms sql-server-2008-r2

【解决方案1】：

获取会员付款：

public List<Payment> GetMemberPaymnets(int memberId)
    {
        List<Payment> Payments = new List<Payment>();

        string SELECT = "SELECT ID,AMOUNT,STARTDAY,ENDDAY FROM Payments WHERE Id = @Id order by endday desc";

        using (sqlConnection = new SqlConnection(sqlConnectionString_WORK))
        {
            sqlConnection.Open();

            using (SqlCommand sqlCommand = new SqlCommand(SELECT, sqlConnection))
            {
                sqlCommand.Parameters.Add("@Id", SqlDbType.Int).Value = entity.Id;

                var sqlReader = sqlCommand.ExecuteReader();

                while (sqlReader.Read())
                {
                    var payment = new Payment
                    {
                        Id = Convert.ToInt32(sqlReader["Id"]),
                        Amount = Convert.ToDecimal(sqlReader["Amount"]),
                        StartDay = Convert.ToDateTime(sqlReader["StartDay"]),
                        EndDay = Convert.ToDateTime(sqlReader["EndDay"])
                    };

                    Payments.Add(payment);
                }
            }
        }

        return Payments;
    }

而不是

if (member.EntryDate < DateTime.Today)
{
     member.Status = Status.Unpaid.ToString();
}

你可以使用这样的东西

 foreach(Member memeber in memeberList)
 {
        List<Payment> memberPayments=GetMemberPayments(member.Id);
        //also you need to check that memberPayments.Count>0
        if(memberPayments[0].EndDay<DateTime.Today)
        {
           member.Status = Status.Unpaid.ToString();
        }
 }

但如果您不需要对会员付款进行一些操作，您可以制作数据库方法，通过会员ID返回会员付款状态。

【讨论】：

【解决方案2】：

您可以尝试使用Member 查询获取最新的付款日期。而不是

string SELECT = "SELECT * FROM Members ORDER BY Id";

试试

string SELECT = "SELECT m.Id, m.Name, 
m.Surname, m.EntryDate, MAX(p.EndDay) AS EndDay FROM Members m
JOIN Payments p ON p.Id = m.Id
ORDER BY m.Id";

然后替换这个：

if (member.EntryDate < DateTime.Today)
{
     member.Status = Status.Unpaid.ToString();
}

用这个：

var endDate = Convert.ToDateTime(sqlReader["EndDay"])
if (endDate < DateTime.Today)
{
    member.Status = Status.Unpaid.ToString();
}

这假设会员总是有一次付款。如果可能有成员没有付款，则必须进行一些空值检查和左连接。

【讨论】：