How to use?

I want to create a query according to the form filled in by the user.
The query will be run on the web server.

Client

 <riac:DomainDataSource x:Name="dsProducts" AutoLoad="True" QueryName="GetProduct" LoadSize="30" >
      <riac:DomainDataSource.DomainContext>
        <domain:TestDomainContext />
      </riac:DomainDataSource.DomainContext>
      <riac:DomainDataSource.QueryParameters>
        <riac:Parameter ParameterName="filter"  />
      </riac:DomainDataSource.QueryParameters>
      <riac:DomainDataSource.SortDescriptors>
        <riac:SortDescriptor PropertyPath="Name" Direction="Ascending" />
      </riac:DomainDataSource.SortDescriptors>
    </riac:DomainDataSource>

using ex = System.Linq.Expressions;

try {
        System.Linq.Expressions.Expression expRoot = null;
        ex.Expression<Func<Demo.Web.Product, bool>> cc;

        //Build Query
        //-- Price --
        if(!string.IsNullOrEmpty(txtPrice1.Text)) {
          cc = p => p.ListPrice >= decimal.Parse(txtPrice1.Text);
          expRoot = expRoot.LogicalAnd(cc);
        }
        if(!string.IsNullOrEmpty(txtPrice2.Text)) {
          cc = p => p.ListPrice <= decimal.Parse(txtPrice2.Text);
          expRoot = expRoot.LogicalAnd(cc);
        }
        //Size
        if(!string.IsNullOrEmpty(txtSize1.Text)) {
          cc = p => p.Size >= decimal.Parse(txtSize1.Text);
          expRoot = expRoot.LogicalAnd(cc);
        }
        if(!string.IsNullOrEmpty(txtSize2.Text)) {
          cc = p => p.Size <= decimal.Parse(txtSize2.Text);
          expRoot = expRoot.LogicalAnd(cc);
        }
        //Colors
        string[] bikeColors = new String[] { txtColor1.Text, txtColor2.Text, txtColor3.Text };
        ex.Expression expColor = null;
        foreach(var item in bikeColors) {
          if(!string.IsNullOrEmpty(item)) {
            string ss = item.ToUpper();
            cc = p => p.Color.ToUpper().Contains(ss);
            expColor = expColor.LogicalOr(cc);
          }
        }
        expRoot = expRoot.LogicalAnd(expColor);

        byte[] query = null;
        if(expRoot != null) {
          query = expRoot.Serialize();
        }

        dsProducts.QueryParameters[0].Value = query;
        dsProducts.Load();
      } catch {
        MessageBox.Show("Invalid Input");
      }

Server

namespace Demo.Web
{
  using System.Linq;
  using System.Linq.Expressions;
  using System.ServiceModel.DomainServices.Hosting;
  using System.ServiceModel.DomainServices.Server;
  using ExpressionSerialization;


  [EnableClientAccess()]
  public class TestDomainService : DomainService
  {
    [Query(HasSideEffects = true, IsComposable = true)]
    public IQueryable<Product> GetProduct(byte[] filter) //System.Data.Linq.Binary
    {
      ProductList li = System.Web.HttpContext.Current.Session["products"] as ProductList;
      var query = from n in li select n;
      IQueryable<Product> qq = query.AsQueryable();
      //--------------------------------
      if(filter != null) {
        qq = ExpressionExtension.ApplyFilter(qq, filter);
      }
      //--------------------------------
      return qq;
    }
  }
}