Question

I’ve a method that returns this exception.
LINQ to Entities does not recognize the method ‘System.String stringCutter(System.String)’ method, and this method cannot be translated into a store expression.

      public List<ProductReqNoDate> GetRequestsQuery()
    {
      var query = (from r in db.talepler
                     select new ProductReqNoDate
                     {
                         talepEdenBirim = r.talepEdenBirim,
                         talepNo = r.talepNo,
                         talepTarihi = r.talepTarihi,
                         urunAdi = stringCutter((from p in db.urunler
                                                 where p.talepNo == r.talepNo
                                                 select p.urunAd).FirstOrDefault()) // <--This
                     }).AsQueryable();
     return query.ToList();
     }
       string stringCutter(string txt)
    {
        return string.IsNullOrEmpty(txt) ? "" : txt.Length <= 30 ? txt : txt.Substring(0, 30) + "...";
    }

when i use this string operations inline, it works. but its too long,

      urunAdi = ((from p in db.urunler where p.talepNo == r.talepNo select p.urunAd).FirstOrDefault()).Length <= 30 ?
                         ((from p in db.urunler where p.talepNo == r.talepNo select p.urunAd).FirstOrDefault()) :
                         ((from p in db.urunler where p.talepNo == r.talepNo select p.urunAd).FirstOrDefault()).Substring(0, 30) + "..."

How can i refer (from p in db.urunler where p.talepNo == r.talepNo select p.urunAd).FirstOrDefault()) as txt maybe; so i can use stringCutter method inline like:

     urunAdi=string.IsNullOrEmpty(txt) ? "" : txt.Length <= 30 ? txt : txt.Substring(0, 30) + "...";

Is there a way of shortening this code. , thanks

Answer 1

IQueryable<> cannot convert your expression to be used with the back-end store. You need to bring a string into memory first, then you can use IEnumerable<>‘s projection method to call your method, like this:

return (from r in db.talepler
    select new // First, use an anonymous type to read the building blocks
    {
        r.talepEdenBirim,
        r.talepNo,
        r.talepTarihi,
        urunAdiStr = (from p in db.urunler
            where p.talepNo == r.talepNo
            select p.urunAd).FirstOrDefault()
    }
).AsQueryable()
.ToList() // Force the data into memory
.Select(anon => new ProductReqNoDate {
    talepEdenBirim = anon.talepEdenBirim,
    talepNo = anon.talepNo,
    talepTarihi = anon.talepTarihi,
    urunAdi = stringCutter(anon.urunAdiStr) // Now stringCutter is available
}).ToList();