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

user_259227 0
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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?

exception-handling linq-to-entities linq .net c#
7 Answers

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).

user_111273830
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