Dunno

Deriving the Exceptions from Exception class or ApplicationException class

2012-01-31T07:14:00.000-08:00

I was doing a code review today and chanced to look upon msdn to get some guidance around how to work with Exceptions.

Thankfully the guideline around the application specific exceptions derving from ApplicationException has changed and now it is advised that application developers should derive their exceptions from Exception class.

The reason for that is fairly simple. If all application exceptions had to derive from ApplicationException class then it would have meant that something as simple as ArgumentException had to be reinvented. Because applications do have cases where the ArgumentException has to be thrown and in that case i would want to reuse the ArgumentException class provided by the framework. And this class is deriving from the Exception class and not ApplicationException class. So it simply was not working :)

For more details check Remarks section on this msdn page.

~Abhishek

CRM Online :- Setting up an efficient developer environment for SilverLight resources

2011-07-01T03:42:00.000-07:00

I've started working on a project where i am supposed to build a silverlight web resource for CRM Online and test it. The Web Resource will use CRM OData APIs to communicate with the CRM Online system and hence it can be tested only once it is hosted within an HTML page which is hosted in a CRM Online as a web Resource.
Now here are the steps one needs to follow in order to debug this silverlight code..
1) Upload the xap file as a web resource in the CRM Online instance using the Web UI
2) Publish the xap file
3) Navigate to the html file using the URL
4) Attach the IE to visual studio and then debug the code by setting break points

This makes the debugging and developing the applications very tedious since every build means that i have to upload the resource and do navigation as well...
In order to make this process efficient here is the setup i have done on my machine

1) Use Web Resource Upload Utility to upload the xap file on CRM Online instance. Now every time you build your solution all you need to do is to click a button to upload and publish the new xap file to CRM Online instance.
2) In the web project you got created when you create a silverlight project add a new html page where onload of the body redirect the browser to the url where your html file is added. Here's how the code of html might look like...

Set this html page as the startup page when you debug the stuff...

And you are set...
Now every time you change your code the debug process looks like the following
1) Build the silverlight project and use the web resource upload utility to upload the xap file
2) Press F5 and the html page you've in your web project will redirect you to CRM Online where your xap is being hosted

And you are set. I might work on a command line utility to build and publish the xap file on CRM Online instance if it becomes a lengthy project. But for a small POC kind of work this is much more efficient then the normal way one has to follow...

hope this helps
cheers!
~Abhishek

CRM Online :- How to get the organization name

2011-07-01T02:26:00.000-07:00

While working with CRM Online sometimes it is necessary to get the organization name to do some tasks (Like using a Web Resource Upload Utility)

Now in an on premise CRM system the organization name can be found from the URL or from the deployment manager. But there's no such flexibility in case of CRM Online.

To get the organization unique name you need to go to

Settings -> Customization -> Developer Resources and there you would find the name of the organization as you can see in the below screenshot.

This is the organization name you can use to connect to your CRM Online instance with utilities such as Web Resource Upload Utility :)

NJoi!!!

~Abhishek

How to use Sharepoint Cmdlets in powershell

2011-06-13T01:12:00.000-07:00

To use the powershell commandlets in sharepoint 2010 one needs to add the ps snapin Microsoft.SharePoint.PowerShell which can be done using the following command on windows powershell

Add-PSSnapin Microsoft.SharePoint.PowerShell.

Njoi

~Abhishek

CRM 2011 :- Error while Scheduling a report to run

2011-06-08T02:36:00.000-07:00

I tried scheduling a report to run on a daily basis and store the snapshots for the user in the CRM 2011 system. Doing this was simple as i selected the report in the reports view and did the scheduling.
However the report snapshots were not getting displayed at all and every time i tried to open the snapshot it gave an error saying "The selected report is not ready for viewing. The report is still being rendered or a report snapshot is not available. (rsReportNotReady)"

The culprit was the fact that Snapshot isolation was turned on in my reportserver database. To get rid of this error and to allow the snapshots to be running properly i executed the following query on my reportserver databse and i was good to go...

"ALTER DATABASE ReportServer
SET ALLOW_SNAPSHOT_ISOLATION OFF;"

Hope this helps in case you are stuck while trying to schedule the reports in your CRM installation.

~Abhishek

Stunnware Fetch Xml Doesn't show the attribute of an entity

2011-05-25T05:24:00.000-07:00

If you use the Fetch Xml Wizard from Stunnware sometimes you may face an issue where the Wizard doesn't show one of the attributes which you added to an entity in the Attribute Picker. This happened to me recently and when i did a little investigation i figured out that the Wizard maintains a offline metadata cache for your organization in "%localappdata%\Stunnware\Stunnware Tools Metadata Cache" folder to improve performance.
Now sometimes the cache doesn't get refreshed after you make a change in the CRM metadata on the server. To fix this you need to exit the stunnware tools wizard and delete the folder from the path "%localappdata%\Stunnware\Stunnware Tools Metadata Cache" and boom you'd see your changes being reflected on the wizard.

Njoi!!!!

~Abhishek

Reading a VHD File

2011-02-22T23:14:00.000-08:00

If you ever need to read a vhd file for reasons like you lost the password for your vpc etc there's a cool feature in Windows 7 using which you can mount the vhd file on your hard disk.
You can do so by following the steps below
1) Open Computer Management
2) Go to Storage -> Disk Management and click on it
3) Once the Panel opens you can right click on Disk Management and you would see an option called Attach VHD

4) Click on Attach VHD option. It will popup a dialog asking for location of your VHD

5) Browse to you VHD select and click OK on the dialog and Voila all the data on your VHD is mounted as a partition on your machine.

Have fun :)

~Abhishek

Telnet not working on Windows Server 2008

2011-01-05T21:34:00.000-08:00

While trying to test my SMTP server connectivity i wanted to use telnet on my Windows Server 2008 box. So i did the usual thing i.e. went to command prompt and typed "telnet servername port" and voila i got an error which said "'telnet' is not recognized as an internal or external command,operable program or batch file."

Now that's unfair because telnet is supposed to work. Well the good part which microsoft has done with Windows Server 2008 is that they have given everything but its disabled. So to fix it you need to go to Server Manager -> Features -> Add Feature. Select the Telnet client in the wizard which comes up and you are good to go.

~Abhishek

CRM 2011 Beta :- GetGeoCode activity for the CRM Workflows

2010-12-30T01:51:00.000-08:00

With Maps becoming more and more popular way of looking at the data like addresses it has become necessary that we save the addresses of the entities in longitude and latitude format so as to ensure that it can be displayed on the maps easily.
I have an entity called School in my CRM 2011 Beta system and it has an address associated with it. A few of the attributes of entity are
1) Name
2) AddressLine
3) City
4) PostalCode
5) State
6) Country (Defaulted to USA for this discussion)
7) A few more attributes which are not relevant for this discussion

There's a CRM Form where the user of the system goes and creates the entity instances of the system. The requirement is to show all the schools in the CRM system on a Bing Map. Now this can be achieved using various controls and SDKs like Telerik Controls, Bing Map SDK, Open Map Provider for Telerik Controls and some Google Map APIs as well. But most of these SDKs expect a Longitude and Latitude to be provided for the address so that they can quickly pinpoint the location on their map.

Longitude and Latitude is something i can't ask the user to fill as many end users might not understand what it means and most won't have any idea about the latitude and longitude on which the school is present on the map. So the easiest way is to achieve it using a plug in or workflow which can run asynchronously to populate the longitude and latitude of the school entity instance. I chose to do it using a workflow process.
But the question is how would the workflow process determine the longitude and latitude given the Address. The answer to this is that there are various Geocode APIs available. A few popular ones are
1) Yahoo PlaceFinder API
2) Google GeoCode API
3) Bing GeoCode Service
4) Bing Locations API

In my case i chose to use Bing Locations API to find the longitude and location of the given address.

It is a rest based service and can be called by shooting a GET request on the URL in the following format

http://dev.virtualearth.net/REST/v1/Locations/{CountryCode}/{StateCode}/{PostalCode}/{City}/{StreetAddress}?output=xml&key={BingMapKey}

You can get a BingMap API access key for free by creating an account on https://www.bingmapsportal.com/

The sample CRM Activity code which i wrote can be downloaded from here. You can compile this code into a dll. Sign it with a key and register the same using CRM Plugin Registration Utility which ships with CRM SDK.

Njoi the APIs.

~Abhishek

Insufficient Privileges. The logged-on user does not have the appropriate security permissions to view these records or perform the specific action.

2010-12-09T03:32:00.000-08:00

While working on CRM 2011 Beta i created a simple entity model and created a role. On this role i gave read permissions for all the entities in the entity model and then assigned a user to this role.

After this when i logged on to the CRM system using the web client with the user just created i was assuming that i would get all the entities in my workplace and i would be able to work with them. But turned out i got the above message instead which said.

"Insufficient Privileges. The logged-on user does not have the appropriate security permissions to view these records or perform the specific action."

I checked the event viewer and found nothing about this message. So the only option was to look into the CRM trace and figure out what is going wrong.

Here are the steps to enable tracing

1) Make 3 registry entries on the CRM Server box under "HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MSCRM"

a) TraceEnabled of type DWORD 32 bit and set its value to 1

b) C:\CRMTrace of type string and value as "C:\CRMTrace" . It can be any folder path

c) TraceRefresh of type DWORD 32 bit with any value between 0 and 99

Once this is done the CRM tracing is enabled on the machine. However to my surprise the trace was happening in "C:\Program Files\Microsoft Dynamics CRM\Trace" folder and not in the folder which i mentioned in the registry key.

But without the key the tracing doesn't work so let it be there.

Once this is done try to login to the CRM system using the same user and you would see a message in the trace which would look something like

"Crm Exception: Message: Principal user (Id=04becef6-fcf5-df11-96ef-00155d647b03, type=8) is missing prvReadCustomization privilege (Id=7bb3b531-ac45-4977-89c8-b99768e55ab8), ErrorCode: -2147220960"

this basically means that the user is missing a Customization Read privilege in the settings. To fix this we can go in the Setting area as an administrator user and give this privilege to the user or role to which the user belongs.

Hope this helps in case you are stuck with this kind of problem in 2011 - Beta system.

Njoi!!!

~Abhishek

Getting logged on user details in ItemAdding event in SPItemEventReceiver

2010-12-08T05:55:00.000-08:00

I am writing a sharepoint 2010 Custom List event receiver. I am able to get the events which are happening on the list items however there's no obvious way to get the logged on user's details in ItemAdding Event.
This is the event which occurs before the Item is added.
SPContext.Current is null for some reason and hence its kind of a dead end to go towards this path.
A non obvious way to achieve this is by using the following code snippet.

public override void ItemAdding(SPItemEventProperties properties)
{

SPUser user = properties.OpenWeb().AllUsers.GetByID(properties.CurrentUserId)

}

~Abhishek

CRM 2011 Beta :- Querying linked entities from the system using FetchXml

2010-12-04T02:33:00.000-08:00

Many a times there's a requirement on querying the data from entity and joining the data with the linked entity as well.
e.g. If i have a "Student Event" entity in the CRM system which has a many to one relationship with the "Student" event and if i want to display the "Student Event " details on my UI then obviously i would want to display the "name" attribute of the student on the UI as well. Now if i use RetriveMultiple method to get these details it would take more then one hit on the CRM Server to get all the relevant data.
To avoid the round trip on the server i can instead use FetchXml method on the CRM Web service. This method would return all the data to me in the form of xml.
The method takes xml query as input and this xml can be formed using a Stunnware tool which can be downloaded here.
Using this tool we can easily create and test the xml which has to be passed to FetchXml method. However there's a catch. If you use this tool to generate the fetch xml it would generate an xml which would look like

<fetch count="50" mapping="logical" version="1.0">

<entity name="studentevent">

<all-attributes>

<link-entity from="studentid" name="student" to="studentid">

<all-attributes>

</all-attributes></link-entity>

</all-attributes></entity>

</fetch>

and when you execute FetchXml API using this xml you would get all the attributes of the student event entity to be returned however the attributes of the student would not be returned.
To solve this you need to manually edit the xml and add an alias attribute to the linkentity student. So the final xml should look something like

<fetch mapping="logical" count="50" version="1.0">

<entity name="studentevent">

<all-attributes />

<link-entity name="student" from="studentid" to="studentid" alias="studentdetails">

<all-attributes />

</link-entity>

</entity>

</fetch>

and this would get you the attributes of studentdetails entity as well.

This may be a bug in the stunnware tool or may be because it was buit to be used against CRM 4.0. Otherwise the tool is an excellent way to generate the xml to query the CRM System with linked entities.

Njoi!!!
~Abhishek

CRM 2011 Beta :- Creating a Workflow Activity to Generate GUIDs

2010-12-02T05:13:00.000-08:00

I am working on CRM 2011 Beta and one of the scenarios I have to create a new entity instance from within a process (Previously known as CRM Workflow.). One of the attributes of this entity is a text field which is supposed to store a GUID and hence by definition it should be unique per instance of the entity.
I couldn't find a way to generate a GUID on the Process designer. This means i have to write a custom activity which would generate a GUID and pass it on to the next step of creating the entity instance.
In this post i will capture how to create a custom activity. How to register it with CRM 2011 Beta and how to use it in my Process. I will try to attach appropriate snapshots where necessary.

Before starting to do anything we have to download the CRM 2011 Beta SDK from here. I extracted the SDK in C:\Temp on my machine however it can be extracted anywhere you want to.
Of course we will need CRM 2011 Beta to be installed on a machine in order to deploy and test the activity from within a process. We will need Visual Studio 2010 to develop the plug in. (This is not a must as you can use utilities from .NET SDK to build the code however i am going to use Visual Studio 2010 as i have it installed on my box already).

First we will create an activity using Visual Studio

1) Create a New Activity Library type of project in Visual Studio 2010. You can find the template in the Workflow section.

2) Delete the Activity1.xaml File as we are not going to use it.

3) Add a reference to Microsoft.Xrm.Sdk.dll and Microsoft.Xrm.Workflow.dll which can be found in the bin folder inside the folder where you extracted the CRM SDK.

4) After doing this if you compile the project you might get a warning which would say that the above 2 assemblies refer to the Syste.ServiceModel.Web assembly which is not present in the .NET Framework Client Profile target which is defined for the project. Change the target profile of your project to .NET Framework 4. This can be done by going to properties of your Project and changing the Target Framework.

5) Create a class called GenerateGuidActivity deriving from CodeActivity class inside System.Activities namespace. Make sure that it is a public sealed class.

6) To add functionality to the activity we need to override Execute(CodeActivityContext context) method. We will come back to the implementation inside this method.

7) We do not have any input to this process step as it is just supposed to generate a new Guid everytime. So we do not have any input to the activity. However we have to send the Guid as output of the step. So we will just create a property which needs to return this Guid. Since this would be a output parameter for the Activity we would want to define the property as

public OutArgument NewGuid { get; set; }

Note that i have defined argument as type string and not Guid. This is because CRM doesn't understand Guid as output type.

8) In order to ensure that CRM Process designer can understand this as well. We need to decorate the property with an attribute i.e. [Output("NewGuid")]

9) Once this is done we can go ahead and implement the Execute method. That would be simple. Just create a new Guid and set it with the context.

this.NewGuid.Set(context, Guid.NewGuid().ToString());

10) Build your code and make sure that the activity compiles.

11) Since the assembly has to be deployed on a CRM Server it would be a good idea to sign it using a key file and give full trust to the key using caspol.

Now comes the time to deploy this activity to be accessible by CRM Process Designer. To do that we will use the Plugin Registration Tool which ships with CRM 2011 Beta SDK. You can find the code for tool in SDK\tools\pluginregistration folder. Open the solution, build and run it.

12) On the home screen Create a New connection using the menu option. Just enter the server name, user name and a friendly name for the connection.
Press Connect wait for the connection to complete. Once connected the screen would look like the following.

13) Now click Register menu and Choose "Register New Assembly" Option.

14) On the dialog box which opens browse and select the assembly which contains the custom activity we built earlier.

15) Check the Select All checkbox

16) Leave the other values to be default i.e. Isolation Mode = None , Location Where assembly has to be stored = "Database"

17) Click Register Selected Plugins. (PS: You might get a dialog saying that there are no plugins to register. The reason for this may be that the Workflow activity you made earlier is not a public class. You might want to change it to a public class to make this work. Another problem which you might face is an error which says "Public assembly must have public key token." This is happening because you forgot to sign your assembly with a key).

18) Once the registration is successful we can go ahead and give a friendly name to this Workflow Activity using the plugin Registration tool. Just enter the name and press Save. Check the figure below for more clarity.

19) After this you can go and access this custom workflow activity from the Process designer to be used in your process.

Happy coding...

~Abhishek

PS :- Pasting the code of the above exercise....

using System.Activities;

using System;

using Microsoft.Xrm.Sdk.Workflow;

namespace Microsoft.Xrm.CustomWorkflowActivity

{

public sealed class GenerateGuidActivity : CodeActivity

{

protected override void Execute(CodeActivityContext context)

{

this.NewGuid.Set(context, Guid.NewGuid().ToString());

}

[Output("NewGuid")]

public OutArgument NewGuid { get; set; }

}

Problem Accessing Dynamics CRM 2011 Beta services from BCS in Sharepoint 2010

2010-12-01T04:11:00.000-08:00

Dynamics 2011 Beta exposes a new oData based service which can be used to pull data out from the system. I am working on BCS for Sharepoint 2010 for a simple demo and i decided to use this service to pull data from CRM 2011 beta system.
After setting the reference i tried to use the DataContext object to pull data out and got an exception which said
"Request version '1.0' is too low for the response. The lowest supported version is '2.0'."
On digging a little deep i realized that some header mismatch is happening between the oData service and my client.
MSDN social says that in order to change this header from 1.0 to 2.0 i need to target my assemblies to compile and run against .NET 4.0. To my utter surprise Sharepoint 2010 runtime can't load the assemblies which are targeted for 4.0 and hence i had to fall back on using the old way of accessing data from CRM which is using CRM data service. That's bad news as this means i will have to write lot of code which i could have done without.
The good thing though is that i will learn the old way of accessing data from the system. Will try to post some code samples.....

Regards, Abhishek

Enabling live id authentication for sharepoint Server 2010

2010-11-29T07:10:00.000-08:00

I am working on Sharepoint 2010 and needed to enable live id authentication for my website.
Blog from http://www.wictorwilen.se/Post/Visual-guide-to-Windows-Live-ID-authentication-with-SharePoint-2010-part-1.aspx is a great step by step guide to enable the live authentication on your server....

It rocks :)

~Abhishek

CRM 2011 Beta :- Creating large number of Options in an Options Set

2010-11-29T03:32:00.000-08:00

So its been ages since i wrote anything in this space and i feel terrible for not being committed. However that's not the point for which i am here today.
I am here to share a small utility which can help you in developing applications on Microsoft Dynamics CRM 2011 Beta
Recently i have been working on creating a SIF compliant data model using CRM 2011 beta for an education domain offering. While trying create the Options Set for this data model i realized that some of the options like country, Language etc. have up-to 450 (or more) options. So creating an Options Set becomes a time consuming and error prone process.
So me and one of my colleagues (Nishant Rana) decided to write a utility which would help in creating the options in an options set by using CRM 2011 metadata service. The source code for the utility can be downloaded here.

In order to compile and run the utility you would need CRM 2011 SDK on your box. Once you run the utility you would see a form which looks like :-

The input values to the form are

1) User Name :- This is a CRM User Name who has the permission to update the options set

2) Password :- The password for the user

3) Domain :- Domain of the CRM Machine

4) Organization service URL :- Replace the server name and port in the given URL

5) Seed value :- This is the integer value which would be given to the first option in the text file . Other options values would be seed value +1... seedvalue + n

6) Options Set Schema name :- Name of the options set in the CRM schema

7) Select File :- Select the text file which has the options in it.

Happy CRM 2011 coding to all of you. Do share your comments/feedbacks and thoughts on the utility.

~Abhishek

WCF Client The underlying connection was closed: The connection was closed unexpectedly.

2010-06-11T03:05:00.000-07:00

There can be several reasons as to why we get the exception "WCF Client The underlying connection was closed: The connection was closed unexpectedly." on a WCF client. However i hit an interesting reason today.
So here's how my code structure was

[OperationContract]
Response ProcessRequest(Request request)

[DataContract]
enum SomeEnum
{
    [EnumMember]
    Value1 =1,

   [EnumMember]}
      Value2 =2,
}

[DataContract]
class Response
{
    [DataMember]
    string Message;
    [DataMember]
    SomeEnum EnumValue;
}

Now in my implementation i was trying to send a Response object which looked like
Response response = new Response(){Message="Some Message"};
return response;

Now this compiled fine and looked like it would work great however when i called the method ProcessRequest from my WCF client i got an exception message with the text "WCF Client The underlying connection was closed: The connection was closed unexpectedly.". There's no visible and obvious reason as to why this must be happening.
On enabling the WCF tracing i found that the error is in serializing the value of SomeEnum in this response. Apparently the Enum has nothing with value 0 and hence the framework is not able serialize the Response.
Apparently WCF server stack eats up this exception and closes the connection to the client. The exception doesn't even show up on visual studio and hence it is almost impossible to detect what's going on unless we have a server side tracing enabled.

Speaking at the Developer Summit

2010-04-12T00:11:00.000-07:00

All,
I am speaking at the Great Indian Developer Summit on RESTful services. You can check the details of the session here.
You can see the snapshot of the session created by the GIDS people on the right.
I love the snapshot for sure :).

See you all at Developer Summit at IISC Bangalore on 20th April....

~Abhishek

Notes Error: Maximum allowable documents exceeded for a temporary full text index

2009-12-28T01:51:00.000-08:00

While executing FTSearch method on NotesView class you might get an exception which says "Notes

Error: Maximum allowable documents exceeded for a temporary full text index"

The exception occurs when Full Text indexing is disabled on the database and the number of items in the database is huge.

When we try to execute a FTSearch method on such a database a temporary Full Text index is created on the database. The number of items which can be indexed by this temporary index is set to some default value and if the number of items in the database exceeds this default value then we get this exception. We can override this setting in server's notes.ini using the following parameter

TEMP_INDEX_MAX_DOC=number

Once we set this number to a value greater then number of items in the database the API should start working.

More details can be found here.

~Abhishek

Accessing Lotus Notes Database from .NET

2009-12-28T01:44:00.000-08:00

I am working on a project where i need to get some data our of Lotus Notes application and found a couple of ways to extract the data out.

1) Easiest way to extract the data is to use Lotus Notes SDK which gets installed on the system when the Notes Client is installed.
You can set a reference to domobj.tlb and generate a interop assembly to call the APIs. The API documentation can be found on here.
Some of the APIs like search on the NotesDatabase doesn't seem to work and if that's the case then we can use the second approach.

2) The best part of lotus notes is that the data is exposed using ODBC. We can install the ODBC driver can be downloaded and installed from here.Once done we can use the classes from System.Data.Odbc namespace and access the items and their properties.

Will post some tweaks when i start using these things....

~Abhishek

Resource Oriented Architecture - Part 5 (Connectedness)

2009-10-14T02:50:00.000-07:00

One of the important features of web is its connectedness. i.e. almost all the web is interconnected through something called as hyperlinks.

So any resource which is addressable on web can be connected from another resource using a hyperlink. In an application based on ROA all the resources should be connected to each other. Connectedness can be achieved in an application if we choose the right representation for a resource. Xml is used to represent any entity in a RPC based architecture. Xml is a default choice because of the fact that it is structured way to represent the entity, hence can be easily understood by computer programs.

As of today the web service returns the data in the form of Xml to make it machine readable while web application represent the data in HTML format in order to make the data human readable. However what we forget is that there's another representation called XHTML which is nothing but HTML which is also a well formed Xml.

So if we can represent all the resources in XHTML computers can parse it as Xml while human can read it on browser as HTML. This also gives us a way to interconnect all the resources in a ROA based application using hyperlinks.

There's no such rule which says that resources should always use XHTML however that would be the preferable since it merges web application and web service and hence make the life easy.

We can still use Xml to represent the resources however in such a case the link to relevant resources should be embedded in the representation of the resource in order to ensure that the whole system is navigable if the user has link to one resource within a system.

This concludes the 5 part series about resource oriented architecture. The next logical step for me would be to design an application using ROA tenets, which involves identifying the right resources, their representation. I might take an enterprise application to do his exercise.

Hope to find some time to do that....

~Abhishek

Resource Oriented Architecture - Part 4 (Uniform Interface)

2009-10-08T22:36:00.000-07:00

The RPC style services are very good in creating and documenting the contract. However if i look at it from a high level view i am creating a new interface for every service in the world.

Imagine this i can write so many services to manage a CRM account e.g. createAccount, updateAcccount, deleteAccount, addOppurtunity, winOptions, looseOptions so on and so forth i.e. for every conceivable action i want to take on a account i can probably create a new method in the contract. This becomes so difficult to manage when orchestrating the services to come up with a business process. Because its very difficult to understand what services can be called at what stage in a business process.

Now when i give this to a programmer who's building an orchestration using these services. There's no uniformity in the interfaces which allow the programmer to come up with a pattern or a way to know what might be possible in the system. One has to be a domain expert to work with such a system.

That's why ROA proposes to have a uniform interface which should be exposed by the resources inside a system. i.e. once you know the URL of a resource it can support upto 6 methods which are nothing but http verbs. Let's have a look at them

1) OPTIONS :- This is a metadata based verb, i.e. it is supposed to tell the caller as to what all http methods does the resource support.

2) GET :- As the name implies this would return the resource content to the caller. The format of content is another story and we'd discuss in the next tenet.

3) HEAD :- This is supposed to return the http header information to the caller. e.g. when was the content last modified. This is an important verb as based on this we can take advantage of http caching infrastructure.

4) PUT :- This verb is supposed to create or update a resource. Ideally if the request is sent to a non existant URI then we are supposed to create the resource while if the resource exists on the server then it is supposed to be replaced by the new one

5) DELETE :- As the name implies, it can be used to delete or archive the resource.

6) POST :- This is one of the most open ended verb which has been left out in http and hence the most abused one by SOA. Anyways in a ROA this verb can be used either to append content to an existing resource or to create new content where the URI of the newly created resource would be defined by the server.

All in all we can conclude that a resource can support CRUD operations using PUT/POST, GET, PUT/POST, DELETE http verbs, while a resource can define the supported operations using OPTIONS http verb. HEAD is a verb which can be used to take advantage of caching mechanism.

Now once we've this kind of system in place we've to ensure that we define our system in such a way that each entity, state or a stage of business process can be represented as a resource. So in our example of CRM system we can create 3 resources i.e. Account, Oppurtunity, Option

and then both these resources can support GET, PUT, POST and DELETE operations. So createAccount becomes a PUT request to http://crmsystem/account/myAccount/1234, deleteAccount becomes a DELETE request to http://crmsystem/account/myAccount/1234,

addOppurunity becomes a PUT request to http://crmsystem/account/1234/Oppurtunity/1,

winOptions, looseOption can become a POST request to http://crmsystem/account/myAccount/1234/Options/1

The beauty of the whole system lies in the fact that each entity has a URI and each URI supports a uniform interface. So when i give a URI of an opportunity http://crmsystem/account/1234/Opportunity/1) to a programmer in my company, at the very least he knows the following

1) To get the details of the opportunity he has to hit the URI with http GET request

2) To delete the oppurtunity he has to hit the URI with http DELETE request

3) To update the oppurtunity PUT or POST should help

4) To know what is supported OPTIONS can be used.

In this world we literally can live with these verbs and most if not all programming problems can be broken into resources. The business process orchestrations can stream line themselves around these verbs and the world might become much simpler for us as programmers :).

~Abhishek

Resource Oriented Architecture - Part 3 (Addressability)

2009-10-08T02:15:00.000-07:00

URLs is one of very simple and powerful feature of WWW. It is because of URL that everything is discoverable and locatable on the web.

e.g. a builder putting his URL on an advertisement bill board and everyone who hits that URI gets access to all the resources about a project which builder has put on the web.

If we look at a search results of google each page of the search results is a resource and each page has a unique URL.

e.g. http://www.google.com/search?q=India&start=35 will take me to a page which would have the search results for the query "India" and the page contents would start from 35th search result.

In a resource oriented world each resource inside a system would have a unique URL to locate it. e.g. in a CRM system all the accounts would have a unique URL to navigate to them. Which basically means that all the accounts are addressable. If we shoot a "http GET request" to that URL we should be able to get details about that account.

So an account with ID=1234 can be represented as http://crmsystem/account/1234

Even a collection of accounts is a resource e.g. all the accounts from Hyderabad can be resource found by sending a http get request to http://crmsystem/accounts/hyderabad

Note the subtle difference between the URLs. The first URL contains the string account while the second one contains accounts, which signifies that the first resource is just an account while the second one is a collection of accounts.

This approach is very different from classic SOA applications where we'd write 2 web service operations called getAccountbyId(string accountId) and getAccountsForRegion(string region). Both the operations will have a single URL which would be http://crmsystem/services and can be invoked by sending appropriate SOAP envelope to this URL using http POST method. Its not really intuitive for a user or a machine as to what kind of POST requests one is supposed to send on the URL.

Another important aspect to note about this tenet is that a URL is non-ambiguous and can point to one and only one resource, while a resource can be located by using 2 different URLs. e.g. an account with accountId=1234 which is a top performing account can be represented by 2 different URLs i.e. http://crmsystem/account/1234 and http://crmsystem/account/topPerformer. In this case the URL http://crmsystem/account/1234 points to a static resource and ideally won't change while http://crmsystem/account/topPerformer is a dynamic calculated resource and can point to different resources at different times.

This tenet will closely relate to the next tenet i would discuss in my next post in this series i.e. Uniform Interface.

~Abhishek

URI, URN and URL why 3 terms

2009-10-05T00:16:00.000-07:00

I am attending a training and an interesting question came up while discussing WCF i.e. what is the difference between the terms URI, URN and URL and most of the times we do see the terms being used in various documents and we hardly care about the fact that they are more or less different acronyms and there has to be a difference.
And turns out there's a subtle difference
1) URI :- Uniform Resource Identifier
This is like a base class. i.e. if this term is used then it can mean both URN and URL. Simply signifies that both URL and URN can be used in the context.

2) URN :- Uniform Resource Name
This is a URI which can ensure the uniqueness of a name in a given context. e.g. URN "Flat no. 302". Its unique in an apartment. but apartment name is not present in the URN. We can say that a URN can be used for identification but can't be used to locate a resource without a context

3) URL :- Uniform Resource Locator
This is a URI which can be used to locate a resource. This also is a URI and can ensure uniqueness alongwith the mechanism to locate it. e.g. http://luckyabhishek.blogspot.com is a URL which is unique and also communicates the mechanism to discover/locate it.

Interesting and subtle differences pointed by Ramkumar (Our instructor)

Let me go back to training now as Ram has already figured out that i am not listening to him and doing something else. Alas .. he'd not know that i am blogging the discussion we just had ....

~Abhishek

Unit Tests for registry read fails in Visual Studio on 64 bit machines

2009-09-23T01:55:00.000-07:00

My my my...
A hotch potch of Windows Server 2008 and Visual Studio 2008 on a 64 bit machine killed my 3-4 hours today...

So here's the deal
I've a method in one of my dlls which reads a certain value from a sub key of HKEY_LOCAL_MACHINE\SOFTWARE Then i wrote a unit test to test this method. Turns out it fails to read the Registry. I was amazed because registry entry did exist in the registry. After struggling for about an hour or so i decided to write a console application to test the method. And the method worked :O. So now i was in a situation where a method works from the console application while fails from a unit test.

I thought that its a permissions issue so i gave full trust to both the assemblies i.e. unit test assembly and the assembly i was testing. Even that didn't help.
Looking at the task manager of the system i saw that the unit tests run under a process call VSTestHost.exe. So next i tried to give full trust to this exe however that's not possible since it is a win32 exe.

A relook at the Task Manager showed me that the process runs under VSTestHost.exe*32 means a 32 bit process running on a 64 bit OS. Nothing suspicious about it in the first look. However if you look at the nodes below HKEY_LOCAL_MACHINE\SOFTWARE in the registry you see a node called Wow6432Node and that made me think. After some search i figured out that if you run a 32 bit process on a 64 bit machine and try to read the subkeys of HKEY_LOCAL_MACHINE\SOFTWARE The registry reads are actually directed to HKEY_LOCAL_MACHINE\SOFTWARE\Wow6432Node. So i made an entry in this node and it worked.

Lesson :- Be careful while working with registries if you depend on registry for your program to work.

Happy coding :)

~Abhishek