Problem with converting int to string in Linq to entities

Question

var items   from c in contacts             select new ListItem                               Value   c ContactId    Cannot implicitly convert type  int   ContactId  to  string   Value                   Text   c Name                var items   from c in contacts             select new ListItem                               Value   c ContactId ToString      Throws exception  ToString is not supported in linq to entities                  Text   c Name                  Is there anyway I can achieve this  Note  that in VB NET there is no problem use the first snippet it works just great  VB is flexible  im unable to get used to C  s strictness

User · Answer

Brian Cauthon s answer is excellent  Just a little update  for EF 6  the class got moved to another namespace  So  before EF 6  you should include    System Data Objects SqlClient   If you update to EF 6  or simply are using this version  include   System Data Entity SqlServer   By including the incorrect namespace with EF6  the code will compile just fine but will throw a runtime error   I hope this note helps to avoid some confusion

User · Answer

If your  contact  is acting as generic list  I hope the following code works well   var items   contact Distinct   OrderBy c   gt  c Name                                 Select  c   gt  new ListItem                                                                 Value   c ContactId ToString                                    Text   c Name                                     Thanks

User · Answer

I ran into this same problem when I was converting my MVC 2 app to MVC 3 and just to give another  clean  solution to this problem I want to post what I did     IEnumerable lt SelectListItem gt  producers   new SelectList Services GetProducers         ID    Name   model ProducerID     GetProducers   simply returns an entity collection of Producers   P S  The SqlFunctions StringConvert didn t work for me

User · Answer

I solved a similar problem by placing the conversion of the integer to string out of the query  This can be achieved by putting the query into an object    var items   from c in contacts             select new                                Value   c ContactId                  Text   c Name                var itemList   new SelectList    foreach  var item in items        itemList Add new SelectListItem  Value   item ContactId  Text   item Name

User · Answer

Can you try   var items   from c in contacts         select new ListItem                       Value   Convert ToString c ContactId                Text   c Name

User · Answer

My understanding is that you have to create a partial class  to  extend  your model and add a property that is readonly that can utilize the rest of the class s properties   public partial class Contact      public string ContactIdString            get               return this ContactId ToString                      Then  var items   from c in contacts select new ListItem       Value   c ContactIdString       Text   c Name

User · Answer

SqlFunctions StringConvert will work  but I find it cumbersome  and most of the time  I don t have a real need to perform the string conversion on the SQL side   What I do if I want to do string manipulations is perform the query in linq-to-entities first  then manipulate the stings in linq-to-objects  In this example  I want to obtain a set of data containing a Contact s fullname  and ContactLocationKey  which is the string concatination of two Integer columns  ContactID and LocationID       perform the linq-to-entities query  query execution is triggered by ToArray   var data       from c in Context Contacts    select new          c ContactID         c FullName         c LocationID       ToArray        at this point  the database has been called and we are working in    linq-to-objects where ToString   is supported    Key2 is an extra example that wouldn t work in linq-to-entities var data2       from c in data     select new          c FullName         ContactLocationKey   c ContactID ToString           c LocationID ToString           Key2   string Join      c ContactID ToString    c LocationID ToString           ToArray      Now  I grant that it does get cumbersome to have to write two anonymous selects  but I would argue that is outweighed by the convenience of which you can perform string  and other  functions not supported in L2E  Also keep in mind that there is probably a performance penalty using this method

User · Answer

public static IEnumerable lt SelectListItem gt  GetCustomerList                         using  SiteDataContext db   new SiteDataContext                                  var list   from l in db Customers AsEnumerable                              orderby l CompanyName                            select new SelectListItem   Value   l CustomerID ToString    Text   l CompanyName                     return list ToList

User · Answer

if you use entity framework and you want to make the only int acceptable then you can use this in linq query you can try this   var items   from c in contacts         select new ListItem                       Value    int ContractId              Text   c Name              it will work because using  int  will cast your value to the int so you don t need any conversion for string to int and you get the result you want   this worked for me in my project i think it would be helpful for you

User · Answer

Using MySql  the SqlFunctions StringConvert didn t work for me   Since I use SelectListItem in 20  places in my project  I wanted a solution that work without contorting the 20  LINQ statements   My solution was to sub-class SelectedListItem in order to provide an integer setter  which moves type conversion away from LINQ   Obviously  this solution is difficult to generalize  but was quite helpful for my specific project   To use  create the following type and use in your LINQ query in place of SelectedListItem and use IntValue in place of Value   public class BtoSelectedListItem   SelectListItem       public int IntValue               get   return string IsNullOrEmpty Value    0   int Parse Value             set   Value   value ToString

User · Answer

One more solution   c ContactId        Just add empty string and it will be converted to string

User · Answer

Use LinqToObject    contacts AsEnumerable    var items   from c in contacts AsEnumerable               select new ListItem                               Value   c ContactId ToString                    Text   c Name

User · Answer

var selectList   db NewsClasses ToList lt NewsClass gt    Select a   gt  new SelectListItem       Text   a ClassName      Value   a ClassId ToString         Firstly  convert to object  then toString   will be correct

User · Answer

var items   from c in contacts select new ListItem       Value   String Concat c ContactId     This Works in Linq to Entity      Text   c Name      I found that SqlFunctions StringConvert  double c Age  did not work for me either the field is of type Nullable lt Int32 gt   Took me a lot of searching over the last few days of trial and error to find this   I hope this helps a few coders out there

User · Answer

With EF v4 you can use SqlFunctions StringConvert   There is no overload for int so you need to cast to a double or a decimal   Your code ends up looking like this   var items   from c in contacts             select new ListItem                               Value   SqlFunctions StringConvert  double c ContactId  Trim                    Text   c Name

[c#] Problem with converting int to string in Linq to entities

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