Question

I know IQueryable yields no result but just an expression builder, my problem is how can actually use it to execute query and return the set as List to be able to bind it on a grid.

  IQueryable query = _campaignManager.GetCampaign(filter, values);

  // this line returns error
  List<Campaign> campaigns = query.Cast<Campaign>().ToList();

  grdCampaigns.DataSource = campaigns;
  grdCampaigns.DataBind();

additional details: GetCampaign()

    public IQueryable GetCampaign(string filter, params object[] values)
    {
        string parameters = string.Empty;
        foreach (object obj in values)
        {
            parameters += obj.ToString() + ",";
        }

        parameters.Remove(parameters.Count() - 1, 1);

        var query = context.Campaigns.Where(filter, parameters)
           .Select("new(CampaignID,CampaignName)");

        return query;
    }

I’m using DynamicQueryable for dynamic linq queries

The .Select Extension method of the DynamicQueryable

     public static IQueryable Select(this IQueryable source, string selector, params object[] values)
    {
        if (source == null) throw new ArgumentNullException("source");
        if (selector == null) throw new ArgumentNullException("selector");
        LambdaExpression lambda = DynamicExpression.ParseLambda(source.ElementType, null, selector, values);
        return source.Provider.CreateQuery(
            Expression.Call(
                typeof(Queryable), "Select",
                new Type[] { source.ElementType, lambda.Body.Type },
                source.Expression, Expression.Quote(lambda)));
    }

IQueryable .Where() extension

       public static IQueryable Where(this IQueryable source, string predicate, params object[] values)
    {
        if (source == null) throw new ArgumentNullException("source");
        if (predicate == null) throw new ArgumentNullException("predicate");
        LambdaExpression lambda = DynamicExpression.ParseLambda(source.ElementType, typeof(bool), predicate, values);
        return source.Provider.CreateQuery(
            Expression.Call(
                typeof(Queryable), "Where",
                new Type[] { source.ElementType },
                source.Expression, Expression.Quote(lambda)));
    }

thanks…

Answer 1

IQueryable can be of type T e.g.
IQueryable query=+CampaignManager.GetCampaign

but since you are using IQueryable you can use

var enumerator= c.GetEnumerator();
            while (enumerator.MoveNext())
            {
             //add these records to some collection say Collection or Campaign or Create any entity with Name and Id and then assign that collection to DataSource    
            }

i have tried that it’s working you can proceed wit it.