Wednesday, September 16, 2015

LINQ: Problem with Deferred execution

This morning I started my day googling for an exception in the code:
Some part of your SQL statement is nested too deeply. Rewrite the query or break it up into smaller queries
And as most cases, I ended up with a Stackover solution:

The code that I was cleaning up was as bellow:

This was breaking for large data but working fine for small data.

It was breaking when the Except() is used to compare large data – the reason is EF most cases does Deferred execution- so all the incompleteCourseId, completedCourseId and requeriedCourseId are evaluated when the Except() is called. For small data it can execute – but for large data it breaks.

Similar thing can happen when complex query needs to be executed through LINQ; So possibly its a good idea to split the queries into multiple ones and evaluate whenever required/whenever requires fetching large data.

So the solution is I forcefully evaluated each of the query using ToList() and it seems it is working good now. Off course cost is multiple SQL call.


Monday, June 15, 2015

Passing EventArguments to RelayCommand in MVVM

I was to override the default behavior of the editable ComboBox control. Where if clicked the in the combobox the text will always be selected.

The View :
<ComboBox x:Name="cboList" FontSize="25"
     TabIndex="8" MaxDropDownHeight="270"
     Style="{DynamicResource ComboBoxStyleLargeScroll}"
     DisplayMemberPath="Name" SelectedValuePath="RepID"
     ItemsSource="{Binding VisitorHostList, UpdateSourceTrigger=PropertyChanged
   ,ValidatesOnExceptions=True, ValidatesOnDataErrors=True, NotifyOnValidationError=True}"
     SelectedItem="{Binding UpdateSourceTrigger=PropertyChanged, ValidatesOnExceptions=True, ValidatesOnDataErrors=True
   ,NotifyOnValidationError=True, Path=SelectedVisitorHost}"
     SelectedValue="{Binding Inductee.HostRepID, UpdateSourceTrigger=PropertyChanged
   ,ValidatesOnExceptions=True, ValidatesOnDataErrors=True, NotifyOnValidationError=True}" IsEditable="True" VerticalContentAlignment="Bottom" MinWidth="0" MaxWidth="351">
                                        <Style TargetType="{x:Type ScrollBar}">
                                            <Setter Property="Width" Value="50" />
                                        <i:EventTrigger EventName="GotFocus">
                                            <cmd:EventToCommand Command="{Binding GotFocusCommand, Mode=OneWay}" MustToggleIsEnabledValue="True"/>
                                        <i:EventTrigger EventName="PreviewMouseUp">
                                            <cmd:EventToCommand Command="{Binding PreviewMouseUpCommand, Mode=OneWay}" MustToggleIsEnabledValue="True" PassEventArgsToCommand="True" />

The ViewModel :
#region Commands
  public ICommand PreviewMouseUpCommand { get; set; }
#region Constructor
        public MyViewModel()
            PreviewMouseUpCommand = new RelayCommand<MouseButtonEventArgs>(PreviewMouseUp);
#region eventhandler
private void PreviewMouseUp(MouseButtonEventArgs e)
                System.Windows.Controls.ComboBox cboHostList = e.Source as System.Windows.Controls.ComboBox;
                if (cboHostList != null)
                    var cboEditableTextBox = (cboHostList.Template.FindName("PART_EditableTextBox", cboHostList) as System.Windows.Controls.TextBox);
                    if (cboEditableTextBox != null && !cboHostList.IsDropDownOpen)
                        Application.Current.Dispatcher.BeginInvoke(new Action(() =>
            catch(Exception ex)
                Util.Logger(typeof(MyViewModel)).Error("Error in PreviewMouseUp of ComboboxList", ex);

Friday, May 22, 2015

Custom ActionFilter in ASP .Net MVC

I had a scenario like if a person doesn't have proper access to a resource he will receive a message on a page.
Initially I thought I should implement custom Authorization Filter [customize the existing Authorization Filter] - but it looked like Authorization filter is implemented [at least in my application] more like if the filter is not met you are redirected to login page - kind of session checking and stuffs like mandatory things for each of the Actions.
But in my case I was putting this check on a single Action - off course having option to reuse the filter later.
Following is the Controller with Filter:

public ActionResult Siteinfo(int id = 0, string nodeType = "")
RASSiteDetailsModel model = null;
return View(model);

The  PermittedSiteActionAttribute lokked like :
public class PermittedSiteActionAttribute : FilterAttribute, IActionFilter
        bool _IsAuthorised = false;
        void IActionFilter.OnActionExecuted(ActionExecutedContext filterContext)
                if (!_IsAuthorised)
                    filterContext.Controller.ViewData.Model = null;
            catch (Exception ex)
                Logger.Error("Error in PermittedSiteActionAttribute>OnActionExecuted", ex);
        void IActionFilter.OnActionExecuting(ActionExecutingContext filterContext)
                var actionParams = filterContext.ActionParameters;
                object siteId;
                actionParams.TryGetValue("id", out siteId);
                if (siteId != null && decimal.Parse(siteId.ToString()) > 0)
                    Util util = new Util();
                    _IsAuthorised = util.IsPermittedSite(decimal.Parse(siteId.ToString()));
                if (!_IsAuthorised)
                    filterContext.Controller.ViewBag.AuthorizationMessage = "You are not Authorised to access this resource; Please select a different site.";
            catch(Exception ex)
                Logger.Error("Error in PermittedSiteActionAttribute>OnActionExecuting", ex);
Here OnActionExecuting event I am checking the permission and if fails I am setting the Model to be Null at OnActionExecuted event - so that the user doesn't views the resource returned by the Action. May be not the perfect way of doing this - but a way around, I guess :)

To get started with these Asp .Net Action filters following tutorial is a good one:

Open source Push Server

  • PushSharp: [C#] :A server-side library for sending Push Notifications to iOS (iPhone/iPad APNS), OSX (APNS 10.8+) Android (C2DM and GCM - Google Cloud Message), Chrome (GCM) Windows Phone, Windows 8, Blackberry (PAP), and Amazon (ADM) devices!
  • PushSharp.Web: [C#] A web wrapper for PushSharp
  • AeoroGear UnifiedPushSeerver: [JAVA]: Easy and promising - does have a Openshift gear and can be tested over Openshift
  • Pushd:[Node.js] :Pushd is a pluggable "unified" push server for server-side notification to mobile native apps, web apps etc. With pushd you can send push notifications to any supported mobile platform, web app or HTTP server from a single entry point. Pushd takes care of which device is subscribed to which event and is designed to support an unlimited amount of subscribable events.
  • [Node.js]: Loopback is basically a nodejs framework to easily create api - but it does have component to create push servers.
  • Node-Push-Server: [Node.js]: It looks like a stripped down version of Pushd.

Thursday, May 21, 2015

Logging in DotNet applications

  • log4net: log4net from Apache is a library tool to help the programmer output log statements to
    a variety of output targets. log4net is a port of the excellent Apache log4j™ framework to the Microsoft® .NET runtime. We have kept the framework similar in spirit to the original log4j while taking advantage of new features in the .NET runtime.
  • ELMAHELMAH (Error Logging Modules and Handlers) is an application-wide error logging facility that is completely pluggable. It can be dynamically added to a running ASP.NET web application, or even all ASP.NET web applications on a machine, without any need for re-compilation or re-deployment.For applications to log without putting any code inside the applications

WCF vs Asp.Net Web API

When I first learnt about Web API, I got confused - as I was always doing the RESTful services using the WCF - why then another way to accomplish the same thing ?

  • Back-end Services
  • SOAP, WS-*
  • Transporst: HTTP, UDP, TCP, QUEUES, Custom
  • Message Patterns: request-response, one-way, duplex
  • Use WCF Web HTTP to add HTTP endpoints to existing WCF Services
  • Use WCF Data Services for full OData support
  • Front-end Services
  • Media Type: JSON, XML, form-URL-encoded, Custom
  • Request-reply only
  • REST, resource centric
  • Use SignalR for asynchronous signaling (polling, long-polling, WebSockets)

For further reference:

Friday, May 9, 2014

Opensource tools for Analyzing Website Traffic Stats

While developing reports fr one of my applications I have got some interest in data and analytic - while googling I have got some of the good works that are open sourced :) [There are always some good folks online :B] . I am listing couple of the tools here:

"Hummingbird lets you see how visitors are interacting with your website in real time."
Hummingbird is built on top of Node.js, and utilizes Websocket to provide 'Live' stats.
Platform : Node.js and javascript

"Piwik is the leading open source web analytics platform that gives you valuable insights into your website’s visitors, your marketing campaigns and much more, so you can optimize your strategy and online experience of your visitors."
Platform: PHP- MySql

For more of them check the list in the following link :

Monday, October 28, 2013


I was trying to convert the following query to LINQ :

select Osid,OsName,CompanyId,Pid,description,type from OrganisationStructure where OSId in (" + location + ") and type='location'
Where location is a string like '123,2345,12356' ...
What I got on some places the where in clause is converted as bellow :

List<string> locList = location.Split(',').ToList();
var orgloc = (from b in context.OrganisationStructures
                                  where locList.Contains(b.OSId.ToString()) select new{b.OSId,b.OSName,b.CompanyId,b.pID,b.description,b.Type});
This was not giving any error on design time. But while debugging I got the following error:
LINQ to Entities does not recognize the method 'System.String ToString()' method, and this method cannot be translated into a store expression
The reason is LINQ to SQL doesn't know how to translate the .ToString() call to a SQL expression.Therefore I had to change it like bellow:
var orgloc = (from b in context.OrganisationStructures select new{b.OSId,b.OSName,b.CompanyId,b.pID,b.description,b.Type}).ToList().Where( s => locList.Contains(s.OSId.ToString()) && s.Type.Equals("location") ) ;

Refrence :

Wednesday, October 9, 2013

Opensource Chatbots/Chatterbots

I have started playing with a Program-O a chatbot that really worked for me. Liked it very much and while googling a little more I have found there is a good community who work for creating chatbots - thought I might list them so that I can check them later; Right now I am just listing and will update this post once I check each of them :

Some other good references I have got from