按日期分组的实体框架总和时间

Question

I have the following code and I get the error

Cannot implicitly convert type 'string' to 'long'

The error is coming from (i => i.TotalHours) .

What am I doing wrong? Or what do I have to change?

Table

ViewModel

private void CalculateTime()
{
    var result = context.TimeSheets.GroupBy(o => o.StartDate)
                        .Select(g => new { StartDate = g.Key, total = g.Sum(i => i.TotalHours) });

    foreach (var group in result)
    {
        Console.WriteLine("StartDate = {0} TotalHours={1}", group.StartDate, group.total);
    }
}

Class:

public class TimeSheet
{
    [Key]
    public int ID { get; set; }

    [StringLength(255)]
    public string MachineID { get; set; }

    public DateTime StartDate { get; set; }

    public DateTime StartTime { get; set; }

    public DateTime EndDate { get; set; }

    public DateTime EndTime { get; set; }

    [StringLength(225)]
    public string WorkDescription { get; set; }

    [StringLength(225)]
    public string ClientName { get; set; }

    [StringLength(225)]
    public string UserName { get; set; }

    public string TotalHours { get; set; }
}

Answer 1

According to your error I believe you need either to change your TotalHours type to long or to make a type conversion, try: (long)Convert.ToDouble(i.TotalHours)

var result = context.TimeSheets.GroupBy(o => o.StartDate)
                    .Select(g => new { StartDate = g.Key, total = g.Sum(i => (long)Convert.ToDouble(i.TotalHours)) });