Linq Error "Could not find an implementation of the query pattern for source type 'System.Linq.IQueryable' Join Not Found'...

Question

What the hell does this mean? Ignore the return, and the get, The results will be flattened and stuck in the application mem (so this will be a set... probably)

"Could not find an implementation of the query pattern for source type 'System.Linq.IQueryable'. 'Join' not found. Consider explicitly specifying the type of the range variable 'a'."

private CommonDataResponse toCommonData
        {
            get
            {
                CommonDataResponse toCommonData = this.gatewayReference.GetCommonData();
                Array dCountries = toCommonData.PropertyCountries.ToArray(); //Webservice sends KeyValuePairOfString
                Array dRegions = toCommonData.Regions; //Webservice sends Array
                Array dAreas = toCommonData.Areas; //Webservice sends Array

                    var commonRAR = from a in dAreas
                        join r in dRegions
                         on a.RegionID equals r.Id
                        join c in dCountries
                         on r.CountryCode equals c.Key
                        select new {c.Value, r.Name, a.Name, a.Id };



                    return toCommonData;
            }
        }

dRegions/dAreas Both arrays, dCountries is .toArray()

Answer 1

Array is a very loose type, and doesn't implement IEnumerable<T> etc. You could try just switching the Array lines to var (let the compiler pick the type). If it still uses Array, then perhaps use .Cast<T>() to specify the type (or Array.ConvertAll, etc).

From Array (without more information) all it knows is object.

Basically, Join is defined (as an extension method) on IEnumerable<T> and IQueryable<T> - not IEnumerable (without the <T>).