Issues omitting the 'where' clause when using System.Linq.Dynamic (Dymanic LINQ API)

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I'm trying to use the LINQ Dynamic Query Library posted here - http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx

The following works great:

List<string> paramsList = new List<string> {"CustomerID"};
        var customer =
            ctx.Customers.Where(cus=>cus.CompanyName.Contains("A")).Select("new(" +
                                 string.Join(", ", paramsList.ToArray()) +
                                 ")");

However if I omit the "Where" clause and do something like this

XML

List<string> paramsList = new List<string> {"CustomerID"};
        var customer =
            ctx.Customers.Select("new(" +
                                 string.Join(", ", paramsList.ToArray()) +
                                 ")");

I get the following error:

CSS

'new' cannot be resolved into a valid type constructor or function., near function, method or type constructor

What am I missing here?

Posted 26-Jan-11 13:43pm

cranialsurge

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dasblinkenlight 26-Jan-11 20:14pm

Are you certain that ctx.Customers has at least one customer with a company name containing capital "A"?..

cranialsurge 26-Jan-11 20:22pm

@dasblinkenlight: Yea, which is why the first code block returns those results. The second one should return everything, but I get the error I posted above instead.

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cranialsurge · Answer 1 · 2011-01-28T10:21:00

Solution 2

Got a reply to my question on the MSDN forums:

http://goo.gl/KwikB

Posted 28-Jan-11 10:21am

cranialsurge

dasblinkenlight · Answer 2 · 2011-01-26T15:28:00

I tried both your examples, and they completed fine. The first query returned 75 rows; the second one returned 91 rows. I downloaded samples from Scott's page, opened his DynamicQuery project, and modified the Main() as follows:

C#

//Copyright (C) Microsoft Corporation.  All rights reserved.

using System;
using System.IO;
using System.Collections;
using System.Collections.Generic;
using System.Text;
using System.Linq;
using System.Linq.Expressions;
using System.Reflection;
using System.Linq.Dynamic;
using System.Windows.Forms;
using NorthwindMapping;

namespace Dynamic
{
    class Program
    {
        static void Main(string[] args)
        {
            Northwind db = new Northwind("Data Source=localhost;Initial Catalog=northwind;Integrated Security=SSPI;"); 
            List<string> paramsList = new List<string> { "CustomerID" };
            var customer =
                db.Customers.
                //Where(cus=>cus.CompanyName.Contains("A")).
                Select("new(" +
                                     string.Join(", ", paramsList.ToArray()) +
                                     ")");
            var count = 0;
            foreach (var x in customer) {
                Console.WriteLine(x);
                count++;
            }
            Console.WriteLine("Returned {0} customers", count);
            Console.ReadLine();
        }
    }
}

This code ran to completion with no errors, with Where clause commented and uncommented.

Are we running different versions of his System.Linq.Dynamic? I was unable to locate the code that would produce the error message that you reported in Scott's implementation.