Question

We are trying to cast an instance of IQueryable<EntityObject> to an IQueryable<SpecificEntityObject>, the SpecificEntityObject type is only known at runtime.

We have tried using the code below, which does not compile because The type or namespace ‘objType’ does not exist.

var t = query.ElementType;
Type objType = typeof(IQueryable<>).MakeGenericType(t);
var typed = query.Cast<IEnumerable<objType>>();


var grouped = typed.GroupByMany(groupBy.Select(grp => grp.Expression).ToArray());

Any ideas?

Answer 1

Use following IQueryable extension generic method query.ToDTO<sourceType,DestType>();:

public static class QueryableExtensions
{
    public static IQueryable<TDest> ToDTO<TSource, TDest>(this IQueryable<TSource> source)
    {
        List<TDest> destinationList = new List<TDest>();
        List<TSource> sourceList = source.ToList<TSource>();

        var sourceType = typeof(TSource);
        var destType = typeof(TDest);
        foreach (TSource sourceElement in sourceList)
        {
            TDest destElement = Activator.CreateInstance<TDest>();
            //Get all properties from the object 
            PropertyInfo[] sourceProperties = typeof(TSource).GetProperties();
            foreach (PropertyInfo sourceProperty in sourceProperties)
            {
                //and assign value to each propery according to property name.
                PropertyInfo destProperty = destType.GetProperty(sourceProperty.Name);
                destProperty.SetValue(destElement, sourceProperty.GetValue(sourceElement, null), null);
            }
            destinationList.Add(destElement);
        }

        return destinationList.AsQueryable();
    }
}