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public void Execute(IServiceProvider isp) {
            ITracingService iTrace = (ITracingService)isp.GetService(typeof(ITracingService));
            IPluginExecutionContext context = (IPluginExecutionContext)isp.GetService(typeof(IPluginExecutionContext));
            IOrganizationServiceFactory factory = (IOrganizationServiceFactory)isp.GetService(typeof(IOrganizationServiceFactory));
            IOrganizationService service = factory.CreateOrganizationService(context.UserId);
            if (context.PostEntityImages.Contains("postimage")&& context.PostEntityImages["postimage"] is Entity)
            {
                Entity account = (Entity)context.PostEntityImages["postimage"];
                if (account.Attributes.Contains("parentaccountid"))
                 {
                 if (account.Attributes.Contains("new_bigforagenciescustomer"))
                {
                   QueryExpression child = new QueryExpression{
                       EntityName = "account",
                       ColumnSet = new ColumnSet("parentaccountid"),
                       Criteria = new FilterExpression{
                       Conditions={
                           new ConditionExpression("parentaccountid",ConditionOperator.Equal,account.Id)
                       }}
                   };

                   EntityCollection ec = service.RetrieveMultiple(child);
                    foreach (Entity childs in ec.Entities)
                    {
                        childs["new_bigforagenciescustomer"] = account.Attributes["new_bigforagenciescustomer"];
                        service.Update(childs);
                    }
                }
                 }
            }
        }