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Debug Modern POS using .NET Reflector

Respect to all those POS developers. It really requires some dedication and focus to be a POS developer. This is an example of something I would have not figured out without my colleagues.


We were working on a development project and we struggled to make sense out of the error.

The error we got was complaining about the a method to validate the Unit of measure and Quantity. I was sure the object was not null and I had passed the right thing to it. Unit of measure and quantity fields were populated correctly. The modification was overriding the price.

System.NullReferenceException was unhandled by user code
   HResult=-2147467261
   Message=Object reference not set to an instance of an object.
   Source=Microsoft.Dynamics.Commerce.Runtime.Workflow
   StackTrace:
        at Microsoft.Dynamics.Commerce.Runtime.Workflow.CartWorkflowHelper.ValidateCartLineUnitOfMeasureAndQuantity(RequestContext context, Cart newCart, SalesTransaction salesTransaction, Dictionary`2 salesLineByLineId, CartLineValidationResults cartLineValidationResults)
        at Microsoft.Dynamics.Commerce.Runtime.Workflow.CartWorkflowHelper.ValidateUpdateCartRequest(RequestContext context, SalesTransaction salesTransaction, SalesTransaction returnedSalesTransaction, Cart newCart, Boolean isGiftCardOperation, IDictionary`2 productByRecordId)
        at Microsoft.Dynamics.Commerce.Runtime.Workflow.SaveCartRequestHandler.Process(SaveCartRequest request)
        at Microsoft.Dynamics.Commerce.Runtime.SingleRequestHandler`2.Execute(Request request)
        at Microsoft.Dynamics.Commerce.Runtime.CommerceRuntime.Execute[TResponse](Request request, RequestContext context, IRequestHandler handler, Boolean skipRequestTriggers)
        at ECL.Commerce.Runtime.Donation.TriggerHandlers.SaveCartRequestHandler.Process(SaveCartRequest request)
        at Microsoft.Dynamics.Commerce.Runtime.SingleRequestHandler`2.Execute(Request request)
        at Microsoft.Dynamics.Commerce.Runtime.CommerceRuntime.Execute[TResponse](Request request, RequestContext context, IRequestHandler handler, Boolean skipRequestTriggers)
   InnerException

After many hours over the course a few days we struggled. A colleague suggested to use .NET reflector (this is where you need an experienced retail developer). Using this tool, I was able to make sense of the problem.


Below are the steps to use .NET reflector.

1. Download .NET reflector

https://www.red-gate.com/products/dotnet-development/reflector/

2. Install following wizard. You can use the trial for 14 days or just active it with your serial number

When you install – I would recommend both the desktop and the visual studio extension

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3. Select the assembly to debug. There are a couple of ways you can do that.

Select using the .NET Reflector > Generate PDBs (this will pop up a dialog to select the assembly)

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Alternatively, from your solution explorer. Select the dll that is referenced and click on Enable Debugging.
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4. This will launch the object browser.

Navigate to the method that caused the error. Then right click, Go to Decompiled Definition

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5. I put a breakpoint and run through the process.

What I found was that it code used the salesTransaction object rather than the cartLine to get the unit of measure. Causing a cryptic error about unit of measure/quantity. In other words, I needed to create the cart line and save it to commit it to the salesTransaction first. Then after that process is finished, I can then override the price. i.e. 2 steps rather than trying to it all in one process.

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I hope I don’t get in trouble of advising people to use .NET reflector by blogging here. I just don’t see how else I would have figure this thing out.

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