Using ToString() in LINQ queries?

Question

I have writting a LINQ query to fill a listview but it useses the .ToString() method which apparetly is not allowed. When I use the below code I get the error message:

Error: LINQ to Entities does not recognize the method 'System.String ToString()' method, and this method cannot be translated into a store expression

Is there a way to use the ToString() in LINQ or if that is not possible what is the solution to converting a DateTime to String in the query. Please knot that ReleaseDateName is a string and ReleaseDate is a DateTime

using (var db = new ReleaseInfo())
{
    lvReleaseInfo.DataSource = (from r in db.MediaReleases
                                join rn in db.ReleaseNames
                                on new { MediaReleaseID = r.MediaReleaseID, CultureCodeID } equals new { rn.MediaReleaseID, rn.CultureCodeID }
                                join plat in db.MediaPlatforms
                                on new { MediaPlatformID = r.MediaPlatformID, CultureCodeID } equals new { plat.MediaPlatformID, plat.CultureCodeID }
                                join pub in db.MediaPublishers
                                on new { MediaPublisherID = r.MediaPublisherID, CultureCodeID } equals new { pub.MediaPublisherID, pub.CultureCodeID }
                                join c in db.Countries
                                on new { CountryID = r.CountryID, CultureCodeID } equals new { c.CountryID, c.CultureCodeID }
                                join rd in db.ReleaseDates
                                on new { MediaReleaseID = r.MediaReleaseID, CultureCodeID } equals new { rd.MediaReleaseID, rd.CultureCodeID }
                                join a in db.AffiliateLinks
                                on new { MediaReleaseID = r.MediaReleaseID, CultureCodeID } equals new { a.MediaReleaseID, a.CultureCodeID }
                                where r.SectionID == SectionID
                                select new
                                {
                                    rn.ReleaseTitle,
                                    plat.MediaPlatformName,
                                    pub.MediaPublisherName,
                                    c.CountryName,
                                    ReleaseDate = (rd.ReleaseDate == null ? rd.ReleaseDateName : rd.ReleaseDate.ToString()),
                                    a.AffiliateLinkAddress
                                }).ToList();
    lvReleaseInfo.DataBind();
}

Sergey Kalinichenko Sergey Kalinichenko · Accepted Answer · 2013-05-14T00:43:42

Since you are materializing your query to list anyway, you could do the conversion on the .NET side, rather than in the RDBMS, like this:

...
select new {
   rn.ReleaseTitle,
   plat.MediaPlatformName,
   pub.MediaPublisherName,
   c.CountryName,
   rd.ReleaseDateName,
   rd.ReleaseDate,
   a.AffiliateLinkAddress
}).AsEnumerable() // <<== This forces the following Select to operate in memory
.Select(t => new {
   t.ReleaseTitle,
   t.MediaPlatformName,
   t.MediaPublisherName,
   t.CountryName,
   ReleaseDate = t.ReleaseDateName ?? t.ReleaseDate.ToString()
   t.AffiliateLinkAddress        
}).ToList();

Since the ToString() is called on an element from IEnumerable<T>, it will no longer fail. Also note the use of ?? operator in place of a null-checking ? : conditional.

Using ToString() in LINQ queries?

2 Answers