Question

我有一个包含以下列的DataTable：

| ID |客户编号|付款金额| NextScheduleDate |

所有列均包含字符串值（例如， NextScheduleDate 的第0行单元格可能是字符串“ 11/1/2020”）。我想对其进行过滤，并创建一个仅由 NextScheduleDate 值落在日期范围内的行组成的新DataTable。因此，用户选择范围，该方法应相应地过滤表。 NextScheduleDate 某些单元格值可能为null。我对Linq还是很陌生，因此非常感谢您提供的所有帮助。到目前为止，这是我的方法，根本无法使用。

protected void LoadPayments()
{
    // User provides textbox values
    string startDate = txtStartDateRange.Text;
    string endDate = txtEndDateRange.Text;

    // This methods gets ALL payments, some of which have already happened
    // and some of which are scheduled as future payments
    DataTable tblPayments = Payments.GetAllRecurringPayments();

    // We only want payments where the NextScheduleDate column value is the range selected by the user

    // How to filter so that NextScheduleDate is in between startDate and endDate?
    // (Needs to return values where startDate > NextScheduleDate > endDate

    DataTable futurePayments = tblPayments.AsEnumerable()
    .Where(r => r.Field<string>("NextScheduleDate") == ?????)
    .CopyToDataTable();

    // Bind
    grdPayments.DataSource = futurePayments;
    grdPayments.DataBind();
}

Answer 1

我按原样显示以下代码，但尚未运行。我指出了代码可能在何处中断以及在哪种情况下。

为清楚起见，我假设可以使用Parse方法将您提供的日期转换为DateTime。如果不能，则推理仍然有效，只有您将使用TryParse并为日期无效的情况提供逻辑。

此外，我假设当日期字段的内容为空时，您的数据库返回DBNull.Value。

protected void LoadPayments()
{
    // User provides textbox values
    string startDate = txtStartDateRange.Text;
    string endDate = txtEndDateRange.Text;
    // Converts dates to DateTime (breaks if Dates are not valid)
    DateTime s = DateTime.Parse(startDate);
    DateTime e = DateTime.Parse(endDate);

    // This methods gets ALL payments, some of which have already happened
    // and some of which are scheduled as future payments
    DataTable tblPayments = Payments.GetAllRecurringPayments();

    // We only want payments where the NextScheduleDate column value is the range selected by the user

    // How to filter so that NextScheduleDate is in between startDate and endDate?
    // (Needs to return values where startDate > NextScheduleDate > endDate

    DataTable futurePayments = tblPayments.AsEnumerable()
    .Where(r =>
    {
        // Excludes if there is no date.
        // Assumes the DB returns DBNull.Value if the Field is null
        if (r.Field("NextScheduleDate") == DBNull.Value) { return false; }
        // Breaks if Date is not valid
        DateTime d = DateTime.Parse(r.Field<string>("NextScheduleDate"));
        if (d < s) { return false; }
        if (d > e) { return false; }
        return true;
    });

    .CopyToDataTable();

    // Bind
    grdPayments.DataSource = futurePayments;
    grdPayments.DataBind();
}

查询按日期范围过滤数据表

1 个答案: