sql datetime与字符串进行比较

Question

if i have the following to access an sql database for a date to compare it to a string that a user enters:

public IQueryable<Audit> FindAllAuditsByNameDate(String name, String date)
        {
            return from audit in db.Audits
                   where audit.EventTime.ToString().Contains(date) && audit.User.UserName.Contains(name)
                   orderby audit.User.UserName
                   select audit;
        }

it fails is the user enters the "/" character in a date. how do i work around this?

Answer 1

Try DateTime.Parse . It's able to understand a lot of the common formats for entering DateTimes.

DateTime dateStart = DateTime.Parse(date);
DateTime dateEnd = dateStart.AddDays(1);

return from audit in db.Audits
       where audit.EventTime >= dateStart &&
             audit.EventTime < dateEnd &&
             audit.User.UserName.Contains(name)
       orderby audit.User.UserName
       select audit;

If DateTime.Parse doesn't parse the format you want, you can always use DateTime.ParseExact and provide your own format strings.

Answer 2

Considering EventTime is of type DateTime? you need to check it against its value. First convert the string date to DateTime

DateTime newDate = Convert.ToDateTime(date);
return from audit in db.Audits
                   where audit.EventTime.Value == newDate && audit.User.UserName.Contains(name)
                   orderby audit.User.UserName
                   select audit;

Answer 3

Warning - Don't use Contains .

Disadvantages of Contains

Suppose I have two list objects.

List 1      List 2
  1           12
  2            7
  3            8
  4           98
  5            9
  6           10
  7            6

Using Contains, it will search for each List-1 item in List-2 that means iteration will happen 49 times !!!

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Answer to your original Question

public IQueryable<Audit> FindAllAuditsByNameDate(String name, String date)
{
    DateTime Dt;
    if (DateTime.TryParse(date, out Dt))
    {
        return from audit in db.Audits
                where audit.EventTime.ToString().Contains(date) && audit.User.UserName.Contains(name)
                orderby audit.User.UserName
                select audit;
    }
    return null;
}

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TryParse

1. Returns a bool indicating whether it succeeded.
2. It just try/catch internally that why is implemented without exceptions so that it is fast.
3. Use it in case the value may be InValid.

Parse

1. Throws an exception.
2. Use it if you are sure the value will be valid