getting opportunity products relating to opportunity

Senario: 

we need to retrieve the Opportunity Products relating to opportunity. and update the fields in opportunity product entity.

first retrieve the opportunity products relating to the particular opportunity:


string fetchquery = "<fetch version='1.0' output-format='xml-platform' mapping='logical' distinct='false'>" +
  "<entity name='new_opportunityitproduct'>" +
    "<attribute name='new_opportunityitproductid' />" +
    "<attribute name='new_name' />" +
    "<attribute name='new_category' />" +
    "<attribute name='new_subcategory' />" +
    "<attribute name='new_productservice' />" +
    "<attribute name='new_price' />" +
    "<attribute name='new_actuvalclosedate' />" +
    "<attribute name='new_estclosedate' />" +
    "<attribute name='createdon' />" +
    "<order attribute='new_name' descending='false' />" +
    "<filter type='and'>" +
      "<condition attribute='new_opportunityid' operator='eq' uitype='opportunity' value='" + entity1.Id + "' />" +
    "</filter>" +
  "</entity>" +
"</fetch>";

here : condition attribute is the 1:N  relation between opportunity and opportunity product.

reading the Fetch xml data:


RetrieveMultipleRequest req = new RetrieveMultipleRequest();
                FetchExpression fetch = new FetchExpression(fetchquery);
                req.Query = fetch;
                RetrieveMultipleResponse resp = (RetrieveMultipleResponse)service.Execute(req);

                //oipt.Id = leadids;

                EntityCollection col = resp.EntityCollection;


Ex  Plugin:


using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using Xrm;
using System.Diagnostics;
using System.ServiceModel;
using Microsoft.Xrm.Sdk;
using Microsoft.Xrm.Sdk.Query;
using System.Windows.Browser;
using System.Net;
using System.IO;
using System.ServiceModel.Description;
using Microsoft.Xrm.Sdk.Discovery;
using Microsoft.Xrm.Sdk.Messages;
using Microsoft.Crm.Sdk.Messages;
using Microsoft.Xrm.Sdk.Client;

namespace Kryptos.Actual.Est.dates
{
   public class dateonupdate:IPlugin
    {
        public DateTime actualdate;
        public DateTime estimateddate;

        public IOrganizationService service;
        public IPluginExecutionContext context;

        public void Execute(IServiceProvider serviceProvider)
        {


            IPluginExecutionContext context = (IPluginExecutionContext)
            serviceProvider.GetService(typeof(IPluginExecutionContext));

            Entity entity;

            // Check if the input parameters property bag contains a target
            // of the create operation and that target is of type Entity.
            if (context.InputParameters.Contains("Target") && context.InputParameters["Target"] is Entity)
            {
                if (context.Depth > 1)
                {
                    return;
                }

                // Obtain the target business entity from the input parameters.
                entity = (Entity)context.InputParameters["Target"];

                // Verify that the entity represents a contact.
                if (entity.LogicalName != "opportunity")
                {
                    return;
                }
            }
            else
            {
                return;
            }

            try
            {
                IOrganizationServiceFactory serviceFactory = (IOrganizationServiceFactory)serviceProvider.GetService(typeof(IOrganizationServiceFactory));
                IOrganizationService service = serviceFactory.CreateOrganizationService(context.UserId);

                Entity entity1 = (Entity)context.InputParameters["Target"];

                string fetchquery = "<fetch version='1.0' output-format='xml-platform' mapping='logical' distinct='false'>" +
  "<entity name='new_opportunityitproduct'>" +
    "<attribute name='new_opportunityitproductid' />" +
    "<attribute name='new_name' />" +
    "<attribute name='new_category' />" +
    "<attribute name='new_subcategory' />" +
    "<attribute name='new_productservice' />" +
    "<attribute name='new_price' />" +
    "<attribute name='new_actuvalclosedate' />" +
    "<attribute name='new_estclosedate' />" +
    "<attribute name='createdon' />" +
    "<order attribute='new_name' descending='false' />" +
    "<filter type='and'>" +
      "<condition attribute='new_opportunityid' operator='eq' uitype='opportunity' value='" + entity1.Id + "' />" +
    "</filter>" +
  "</entity>" +
"</fetch>";

                RetrieveMultipleRequest req = new RetrieveMultipleRequest();
                FetchExpression fetch = new FetchExpression(fetchquery);
                req.Query = fetch;
                RetrieveMultipleResponse resp = (RetrieveMultipleResponse)service.Execute(req);

                //oipt.Id = leadids;

                EntityCollection col = resp.EntityCollection;
                EntityReference opp = new EntityReference();
                opp.Id = entity.Id;
                opp.LogicalName = entity.LogicalName;

                Entity opp_product = new Entity();
                opp_product.LogicalName = "new_opportunityitproduct";

                if (entity1.Attributes.Keys.Contains("actualclosedate") == false)
                {
                  
                }


                else
                {                  

                    actualdate = (DateTime)entity1["actualclosedate"];

                  
                }

                if (entity1.Attributes.Keys.Contains("estimatedclosedate") == false)
                {


                }
                else
                {
                    estimateddate = (DateTime)entity1["estimatedclosedate"];
                }


                foreach (var c in col.Entities)
                {
                    opp_product["new_actuvalclosedate"] = actualdate;
                    opp_product["new_estclosedate"] = estimateddate;
                    //opp_product["new_price"] = (Money)c["new_price"];//new Money() { Value = 0 };
                    //opp_product["new_opportunityid"] =
                    opp_product.Id = c.Id;
                    opp_product.LogicalName = c.LogicalName;
                    service.Update(opp_product);
                }          
                  
              


            }

            catch (FaultException<OrganizationServiceFault> ex)
            {
                throw new InvalidPluginExecutionException("An error occurred in the plug-in.", ex);
            }

        }

    }
}