modify linq query to turn field from datetime to string

Question

So I have a linq expression that that selects a group of records between a certain datetime, as chosen by the user. However, after the callDate is used as a datetime type I need it turned into a string before it is output

Current Code:

[ResponseType(typeof(Detail))]
public IHttpActionResult GetDetail(string StartDate, string EndDate)
{
    DateTime StartDateTime = DateTime.ParseExact(StartDate, "yyyyMMddhhmm", null);
    DateTime EndDateTime = DateTime.ParseExact(EndDate, "yyyyMMddhhmm", null);

    var detail = from a in db.Details where (a.callDate >= StartDate && a.callDate <= EndDate) select a

Model:

[Required]
public DateTime callDate { get; set; }

score 1 · Accepted Answer · edited May 23 '17 at 12:30

If you want CallDate to be returned as a string, you need to select your results as a new object type. This can either be a class you have created, or an anonymous type, or just the date. Examples:

//class
IEnumerable<MyConvertedClass> details = db.Details.Where(a => a.callDate >= StartDate && a.callDate <= EndDate)
                                                  .ToList().Select(a => new MyConvertedClass { Id = a.Id, CallDate = a.CallDate.ToShortDateString() });

//where MyConvertedClass looks like this: 
public class MyConvertedClass {
    public int Id { get; set; }
    public string CallDate { get; set; }
}

//just the dates
IEnumerable<DateTime> details = from a in db.Details where (a.callDate >= StartDate && a.callDate <= EndDate) 
                                select a.CallDate;

//anonymous type
var detail = from a in db.Details where (a.callDate >= StartDate && a.callDate <= EndDate) 
             select new { Id = a.Id, CallDate = a.CallDate.ToShortDateString() };

If you are using the anonymous type in the same block it's fine, or returning it from your API, but maybe don't return it from a method to be used elsewhere. It's hard to deal with anonymous types. (http://codeblog.jonskeet.uk/2009/01/09/horrible-grotty-hack-returning-an-anonymous-type-instance/)

EDIT: Okay, so it looks like you are returning the Detail model from your api controller. In this case, you can't change the type of CallDate (unless you create a new class as above), but you can control the format that the Date is serialized in (default is ISO 8601 [2009-02-15T00:00:00Z]. Check this stackoverflow question to see how to set up a custom formatter to output the date in a particular format:

Specifying a custom DateTime format when serializing with Json.Net

I'm attempting to use the class one but on the callDate I get an error of `Cannot implicitly convert type string to System.Date.Time` — Mr.Smithyyy, Jan 28 '16 at 20:17
@Mr.Smithyyy , to confirm, what types are StartDate and EndDate, and what type is CallDate on your Details class and your converted class? — Simon C, Jan 28 '16 at 20:19
Updated my question hopefully it helps. Also I don't think I understand what you mean by converted class, I'm attempting your example with my Model class — Mr.Smithyyy, Jan 28 '16 at 20:23
Ok, so I've made a converted class and no build errors but when I try to run it I get `LINQ to Entities does not recognize the method 'System.String ToString(System.String)' method` — Mr.Smithyyy, Jan 28 '16 at 20:48
K. Updated. Added a tolist so the SQL will execute before it does the string conversion. — Simon C, Jan 28 '16 at 21:06
It worked! I have so much to learn about linq, thank you for the knowledge. — Mr.Smithyyy, Jan 28 '16 at 21:12

modify linq query to turn field from datetime to string

1 Answers1