IEnumerable<> to IList<>

Question

I am using Linq to query my database and returning a generic IList.

Whatever I tried I couldn't convert an IQueryable to an IList.

Here is my code.

I cannot write simpler than this and I don't understand why it is not working.

public  IList<IRegion> GetRegionList(string countryCode)
{
    var query = from c in Database.RegionDataSource
                where (c.CountryCode == countryCode)
                orderby c.Name
               select new {c.RegionCode, c.RegionName}; 

     return query.Cast<IRegion>().ToList(); 
}

This returns an list with the right number of items but they are all empty Please help, I am bloqued with this for a couple of days now

Answer 1

Your select statement returns an anonymous type: new {c.RegionCode, c.RegionName}

This can't be converted to IRegion - that would basically be Duck-typing, which C# doesn't support.

Your linq statement should return a type that implements IRegion - then your code should work.

However it shouldn't run - the Cast<IRegion> should throw a runtime exception.

Basically:

// this isn't anonymous, and should cast
public class MyRegion : IRegion {
    public string RegionCode {get;set;}
    public string RegionName {get;set;}
}

public  IList<IRegion> GetRegionList(string countryCode)
{
    var query = from c in Database.RegionDataSource
                where (c.CountryCode == countryCode)
                orderby c.Name
               select new MyRegion {RegionCode = c.RegionCode, RegionName = c.RegionName}; 

     return query.Cast<IRegion>().ToList(); 
}

---

Update

If the underlying Linq type implements IRegion this can be a lot simpler:

public  IList<IRegion> GetRegionList(string countryCode)
{
    var query = 
        from region in Database.RegionDataSource
        where region.CountryCode == countryCode
        orderby region.Name
        select region; 

     return query.ToList(); 
}

Answer 2

I'm surprised it's not just failing completely - you're trying to cast each result to an IRegion, but you're generating instances of an anonymous type, which certainly won't implement IRegion.

Do you have a concrete type which implements IRegion?