CODEWITHSUNDEEP
c#.netlinqexceptionlinq-to-entities
netmajor
netmajor

Reputation: 6585

Cannot implicitly convert type 'System.Linq.IQueryable' to 'System.Collections.Generic.IList'

I have a method:

public DzieckoAndOpiekunCollection GetChildAndOpiekunByFirstnameLastname(string firstname, string lastname)
{
    DataTransfer.ChargeInSchoolEntities db = new DataTransfer.ChargeInSchoolEntities();
    DzieckoAndOpiekunCollection result = new DzieckoAndOpiekunCollection();
    if (firstname == null && lastname != null)
    {
        IList<DzieckoAndOpiekun> resultV = from p in db.Dziecko
                      where lastname == p.Nazwisko
                      **select** new DzieckoAndOpiekun(
                     p.Imie,
                     p.Nazwisko,
                     p.Opiekun.Imie,
                     p.Opiekun.Nazwisko)
                  ;
        result.AddRange(resultV);
    }
    return result;
}

and error in selected place :

Error 1 Cannot implicitly convert type 'System.Linq.IQueryable<WcfService1.DzieckoAndOpiekun>' to 'System.Collections.Generic.IList<WcfService1.DzieckoAndOpiekun>'. An explicit conversion exists (are you missing a cast?)

Any idea how solve my problem?

Upvotes: 35

Views: 116075

Answers (7)

Daniel Danielecki
Daniel Danielecki

Reputation: 10590

SonarQube reported Return an empty collection instead of null. and I had a problem with the error with casting as in the title of this question. I was able to get rid of both only using return XYZ.ToList().AsQueryable(); in a method with IQueryable like so:

public IQueryable<SomeType> MethodName (...) {
  IQueryable<SomeType> XYZ;
  ...
  return XYZ.ToList().AsQueryable();
}

Hope so it helps for those in a similar scenario(s).

Upvotes: 1

X-Coder
X-Coder

Reputation: 2736

I've got solved my problem this way in EF on list of records from db

ListOfObjectToBeOrder.OrderBy(x => x.columnName).ToList();

Upvotes: 1

kravits88
kravits88

Reputation: 13049

If using a where clause be sure to include .First() if you do not want a IQueryable object.

Upvotes: 6

fuwaneko
fuwaneko

Reputation: 1165

You can replace IList<DzieckoAndOpiekun> resultV with var resultV.

Upvotes: 11

Arseni Mourzenko
Arseni Mourzenko

Reputation: 52371

To convert IQuerable or IEnumerable to a list, you can do one of the following:

IQueryable<object> q = ...;
List<object> l = q.ToList();

or:

IQueryable<object> q = ...;
List<object> l = new List<object>(q);

Upvotes: 54

fletcher
fletcher

Reputation: 13780

You can use the .ToList() method to convert the IQueryable result returned to an IList, as shown below, after the linq query.

   public DzieckoAndOpiekunCollection GetChildAndOpiekunByFirstnameLastname(string firstname, string lastname)
{
    DataTransfer.ChargeInSchoolEntities db = new DataTransfer.ChargeInSchoolEntities();
    DzieckoAndOpiekunCollection result = new DzieckoAndOpiekunCollection();
    if (firstname == null && lastname != null)
    {
        IList<DzieckoAndOpiekun> resultV = from p in db.Dziecko
                      where lastname == p.Nazwisko
                      **select** new DzieckoAndOpiekun(
                     p.Imie,
                     p.Nazwisko,
                     p.Opiekun.Imie,
                     p.Opiekun.Nazwisko).ToList()
                  ;
        result.AddRange(resultV);
    }
    return result;
}

Upvotes: 2

Ryk
Ryk

Reputation: 3102

Try this -->

 new DzieckoAndOpiekun(
                         p.Imie,
                         p.Nazwisko,
                         p.Opiekun.Imie,
                         p.Opiekun.Nazwisko).ToList()

Upvotes: 4

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