Associate/Disassociate plugin messages in CRM

Sample Code –

 public class MyPlugin: IPlugin
    {
        public void Execute(IServiceProvider serviceProvider)
        {
            ITracingService tracingService = (ITracingService)serviceProvider.GetService(typeof(ITracingService));
            IPluginExecutionContext context = (IPluginExecutionContext)serviceProvider.GetService(typeof(IPluginExecutionContext));
            IOrganizationServiceFactory factory = (IOrganizationServiceFactory)serviceProvider.GetService(typeof(IOrganizationServiceFactory));
            IOrganizationService orgService = factory.CreateOrganizationService(context.UserId);

            try
            {
                tracingService.Trace("start plugin execution: {0}", this.GetType().FullName);
                if (context.InputParameters.Contains("Target") && context.InputParameters["Target"] is EntityReference && context.ParentContext == null)
                {
                    tracingService.Trace("Parent Context is null");
                    if (context.MessageName == "Associate")
                    {
                        if(context.InputParameters.Contains("Relationship") &&
                            ((Relationship)context.InputParameters["Relationship"]).SchemaName.Equals("schemaname"))
                        {
                            tracingService.Trace("Relationship Found");
                            if (context.InputParameters.Contains("RelatedEntities") && context.InputParameters["RelatedEntities"] is EntityReferenceCollection)
                            {                                
                                var primaryEntity= (EntityReference)context.InputParameters["Target"];
                                var  relatedEntities= context.InputParameters["RelatedEntities"] as EntityReferenceCollection;
                                                           
                            }                           
                        }  
                    }
                }

                tracingService.Trace("end plugin execution: {0}", this.GetType().FullName);
            }
            catch(InvalidPluginExecutionException)
            {
                throw;
            }
            catch (System.ServiceModel.FaultException<OrganizationServiceFault> ex)
            {
                tracingService.Trace(ex.Detail.Message);
                throw;
            }
            catch (Exception ex)
            {
                tracingService.Trace(ex.ToString());
                throw;
            }
        }

      
    }