Lambda expression

To implement a custom filtering or sorting of a LINQ query, simply implement LINQ lambda expression.


var mainLinqQuery = from someVar1 in someCollection select someVar1;


some while later after typing more lines of code.


var filteredLinqQuery = mainLinqQuery.Where(someVar2 => someVar2.someProperty == itemToFilterBy);


The result of the filtered LINQ query, filteredLinqQuery will be the specific result that we require.

Converting IList to List

I was working and had an error trying to cast from an IList type to a generic List type object.

After trolling the intertubes, I found the following, tried it out and what do we know; it works!

Step 1
Declare an empty generic list of whatever type you want.
eg: List object1 = new List();

Step 2
Use the AddRange method from the generic list class.
eg: object1.AddRange(IList_object);

Left Join revisited.

Remember my post on Friday, the 11th September 2009 about LINQ left joins?
Click here to navigate to the post


As I recently found out, should you attempt to left join 2 complex objects, you MUST instantiate the object of which will be null (the right sequence, object).

A better way to explain this is to provide an example.

C# code
-------
List employeeList = new List();
List companyList = new List();

var linqQuery = from eList in employeeList
join cList in companyList on
eList.CompanyId equals cList.Id
into joinEmpCompany
from jec in joinEmpCompany.DefaultIfEmpty(new Company())
select new
{
// insert whatever values you want here.
}

As you can see above, I instantiate a new Company object as there could be instances where the join will produce null results for the right-hand side (Company object).

Instantiating the Company object when using the DefaultIfEmpty function will allow LINQ to execute and not produce Null Reference errors.

Access to Modified Closure error

I was LINQ-ing today and had this obscure error that didn't have much meaning to until I trolled the tubes and came up with Franc Bouma's blog.

Franc's blog

I realized the error and would like to point out that LINQ doesn't like empty or null values in the WHERE clause. Be careful unless you like to get a generic LINQ error and go bonkers and waste countless hours scratching your head wondering what went wrong.

  245         private void DoNothing(List<SomeObject.SomeClass> someList1, List<SomeObject.RoomRateType> someList2)

  246         {

  247             string rphValue = String.Empty;

  248             List<SomeClass> someClassList = new List<SomeClass>();

  249             SomeClass someObjectVar = new SomeClass();

  250 

  251             foreach (SomeObject.SomeClass someObjectVar in someList1)

  252             {

  253                 if (someObjectVar.RPHSpecified)

  254                 {

  255                     rphValue = someObjectVar.RPH.ToString();

  256                     var linqQuery = from rrl in someList2

  257                                     where (rrl.RatePlanCode == rphValue) && (rrl.Rates[0].Base.AdditionalFeesExcludedIndicator == true)

  258                                     select rrl.RoomRateDescription.Name;

  259 

  260                     foreach (var linqItem in linqQuery)

  261                     {

  262                         someObjectVar.MoreDescription += linqItem;

  263                     }

  264 

  265                     someObjectVar.RphCode = someObjectVar.RPH;

  266                 }

  267             }

  268         }

the "rphValue" variable can be null or empty and although I know that what I am doing may not cause any trouble, I am sure in some more complex situation, the results will be dire

More on MVC

To redirect to another URL, simply return the Redirect function
eg: return Redirect("INSERT_URL_HERE");

MVC allows 1 to use the current http context for validation; As a check on whether the user has logged on or not.

   25             if (HttpContext.User.Identity.IsAuthenticated)

   26             {

   27                 //View my previous blog @ http://zacthetechie.blogspot.com/2009/10/mvc-with-web-services.html

   28                 //on how to access a web service from MVC.

   29                 return View();

   30             }

   31             else

   32             {

   33                 return RedirectToAction("LogOn", "Account");

   34             }

MVC with web services

Recently, I was given the opportunity to play around with MVC

Now, my previous experience with MVC Model is with the conventional SQL database interaction using LINQ to retrieve data.

This time, however, I had to interact with web services. Trolling the web resulted in suggestion such as using a REST architecture structure and others which is quite a good read, especially the post by Rob Conery
Rob Conery - ASPNet MVC : Using Restful Architecture

I decided to experiment with using classes instead and it works. Ok, maybe the guys at the Big Blue will knock me down for this but see below for my explaination

This is what I did.

1. I built a web service library, compiled and NUnit tested thoroughly.
2. In the Model of the MVC Application, I added a "Code File". This resulted in an empty C# file being created.












3. From scratch, I built my Web Service Layer (WSL) class (I wonder if you can just add a class from the "Add") with the required properties to interact with the Web Service library.

    1 using System.Collections.Generic;

    2 using Your_WebService_ObjectName;

    3 using Your_WebService_ObjectName.WSCustomObjects.Availibility.Responses;

    4 using Your_WebService_ObjectName.WSObjects.ResLinkAvailibility;

    5 

    6 namespace MVCDemoApplication.Models

    7 {

    8     public class Your_WebService_Layer_Object

    9     {

   10         #region Private Fields

   11         private Application _app = null;

   12         private ResourceTypes _resourceTypes = null;

   13         private List<Your_WebService_ObjectName.WSCustomObjects.Availibility.Responses.GetResourceTypeResponse>

   14             _getResourceTypeResponseList = null;

   15         #endregion

   16 

   17         #region Public Property

   18         public ResourceTypes ResourceTypes

   19         {

   20             get { return _resourceTypes; }

   21             set { _resourceTypes = value; }

   22         }

   23 

   24         /// <summary>

   25         /// A list of GetResourceType response object.

   26         /// </summary>

   27         public List<Your_WebService_ObjectName.WSCustomObjects.Availibility.Responses.GetResourceTypeResponse> GetResourceTypeResponseList

   28         {

   29             get { return _getResourceTypeResponseList; }

   30             set { _getResourceTypeResponseList = value;}

   31         }

   32         #endregion

   33 

   34         public Your_WebService_Layer_Object()

   35         {

   36             _app = new Application("GUID", "PASSWORD", "Another GUID", "<INSERT_YOUR _ URL_HERE>");

   37             _resourceTypes = new ResourceTypes(_app);

   38             _getResourceTypeResponseList = _resourceTypes.GetResourceType();

   39         }

   40     }

   41 }

4. Added a View that was strongly typed to the class in the Web Service DLL.

And the result generated is as below.