Linq无法转换为ToShortDateString（）

Question

Can you please tell me how to fix the query below. LINQ was formating my dates as written out example: August 8th 2015. I need 8/8/2015. Every attempt i try gives me a different error message. What am i doing wrong.

var orgData = (from d in db.tbl_FormsSubmittedValues
               where d.SiteID == _siteID
               & d.FormID == _formID
               & ((d.tbl_FormsSubmitted.UserID == _userID && _viewOwnOnly) || !_viewOwnOnly)
               & ((_search != "" && d.Value.Contains(_search)) || _search == "")
               select new
               {
                   d.FormSubmissionID,
                   Value = d.ValueDate.HasValue ? d.ValueDate.Value.ToShortDateString(): d.ValueLong != null ? d.ValueLong : d.Value,
                   d.FieldID,
                   d.FormID,
                   d.SiteID,
                   d.tbl_FormsSubmitted,
                   d.tbl_FormsSubmitted.UserID,
               }).ToList();

Original Line That was giving me written out date instead of mm/dd/yyyy

 Value = d.ValueDate != null ? d.ValueDate.ToString() : d.ValueLong != null ? d.ValueLong : d.Value,

Problem Line:

Value = d.ValueDate.HasValue ? d.ValueDate.Value.ToShortDateString(): d.ValueLong != null ? d.ValueLong : d.Value,

Error:

Could not translate expression 'd.ValueDate.Value.ToShortDateString()' into SQL and could not treat it as a local expression.

Answer 1

An alternative to creating a new anonymous object would be to create a new typed object (eg select new Submission() { ... } ) that exposes a read-only property for rendering a short date. This may add some overhead for such a simple operation, but it offers some flexibility (you can format more fields later) and performance (any additional query or filter operations are performed against the database instead of in memory).

Or, you could push the work down the pipe to the presentation layer. Let the code responsible for displaying the data to the user handle converting or displaying the short date and keep your data/business layers lean and open to other interpretations. This would keep you from having to go back and change the query or modify your POCO to accommodate a change in the preference for date format. For example, what if you had another person who preferred the date to be shown as YYYY-dd-MM?

Answer 2

Do the formatting outside of the actual sql. Something like:

orgData = (from d in db.tbl_FormsSubmittedValues
           where d.SiteID == _siteID
           & d.FormID == _formID
           & ((d.tbl_FormsSubmitted.UserID == _userID && _viewOwnOnly) || !_viewOwnOnly)
           & ((_search != "" && d.Value.Contains(_search)) || _search == "")
           select new {
                       d.FormSubmissionID,
                       Value = d.ValueDate.HasValue ? d.ValueDate.Value: d.ValueLong != null ? d.ValueLong : d.Value,
                       d.FieldID,
                       d.FormID,
                       d.SiteID,
                       d.tbl_FormsSubmitted,
                       d.tbl_FormsSubmitted.UserID
                      }).AsEnumerable() //Using this to get the query to run.
           //Anything after this should not be done on the database side.
           .Select(d => new
           {
               d.FormSubmissionID,
               Value = d.ValueDate.HasValue ? FormatDate(d.ValueDate.Value): d.ValueLong != null ? d.ValueLong : d.Value,
               d.FieldID,
               d.FormID,
               d.SiteID,
               d.tbl_FormsSubmitted,
               d.tbl_FormsSubmitted.UserID,
           }).ToList();


static string FormatDate(DateTime date)
{
    return  date.Value.ToShortDateString();
}

This keeps the formatting out of the actual generated sql.

Answer 3

I will recommend:

Value = d.ValueDate.HasValue ? (d.ValueDate.Value.Day + "/" + d.ValueDate.Value.Month + "/" + d.ValueDate.Value.Year) : (d.ValueLong != null ? d.ValueLong : d.Value),

Or doing the toshortstring when displaying the data (If you are using it on a website)

Or even parse the date through javascript using the parsed date (json)