Transaction Integrity with Connected Systems

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Broken pencilWith .NET Interoperability around, it’s very likely you’ll be synchronously calling external web services from C/AL, to exchange data. I won’t go into discussing whether or not this kind of architecture is good (my own position is that it isn’t), you may end up having situations where your C/AL code simply makes a synchronous call to external systems, such as web services.

Any external call is an expected point of failure. An important question you must always have in mind when calling external functions is transaction integrity. When writing code that targets only NAV, the structure of code is largely irrelevant, as long as you are not using COMMITs (which is another thing you should avoid at all costs). However, as soon as you introduce external calls, the structure becomes critically relevant. Critically relevant.

I’ve talked about this during my 2012 NAV TechDays session, and I promised I’d blog about it – so, here it goes.

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Cross-Call State Sharing in Web Services

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imageWeb services in NAV have an interesting feature: they are stateless. For a system which is pretty stateful otherwise, this feature can be outright annoying. You must get used to it, and then make sure you never ever write code as if there was any state preserved on the other end.

The reason for this is simple – there is no actual protocol that you use to communicate with NAV through SOAP. Calls are ad-hoc, essentially atomic, each one can accomplish a great deal of things in a single go, and it makes programming a whole lot simpler. The price you pay is the state. Once you close the connection, the session ends and the transaction commits (or rolls back). Next call starts from scratch.

If you need to preserve any state between the calls, whatever that state might be, you are toast. NAV simply doesn’t support it out of the box. A common misconception is that single-instance codeunits help. They don’t. The single instance is always single per session, and since each call is an isolated session, it means that each single instance codeunit dies at the end of the call.

Pretty annoying, isn’t it?

Well, it is, and it isn’t. I won’t argue about validity of situations where you need to preserve state across multiple web services calls – I am going to show you how to do it when you need it.

And what I’m going to show you works in both NAV 2009 R2 and 2013.

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Generics in .NET Interop for NAV 2013

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image.NET Framework is full of programming conceptual gems, that are now at the fingertips of us poor C/AL folks. One of those is generics. However, the C/AL support for generics at the first glance seems rather limited, and the help file says that you can’t specify data types, and that all generics will be instantiated with System.Object as their type. However, with Microsoft Dynamics NAV 2013, there is a very simple way which allows you to use generics with other data types, as well. So, if .NET Framework Interoperability interests you a slightest bit, here’s a solution. The example below will be for the System.Collections.Generic.Dictionary<,>, and I will show how to use instances of the Dictionary<,> object with any desired data type, without having to pull in any external assemblies. (more…)

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Passing strongly-typed data to Web services

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imagePassing strongly-typed data to NAV Web services can be trickier than it seems. If you are lucky, you can make your method accept strongly-typed parameters, and you are good to go. However, if you just can’t avoid sending text data, your text must be encoded in EN-US format, otherwise it will cause problems (see this).

What the heck, just encode the data as EN-US, right? Not quite. There are a myriad of reasons why data can come in non-EN-US encoding, one of which is this: it’s the Web services, for Pete’s sake – anyone or anything can call them.

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The Beauty and The Beast: NAV and .NET

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imageIf there wasn’t one already, someone should have invented Belgium. There are two things in this world that I love, and probably shouldn’t (and an oversized red speaker’s shirt I got from Luc today did a darned god job at concealing the unlucky consequences of overly indulging in both of them): beer and chocolate. Boy, do Belgians know their beer and chocolate!

But they know their NAV, too, and after NAV TechDays 2011, which have just ended in Antwerp, and two days of top NAV content, I can only say – great job, Luc and the team, and please make it a tradition.

If you attended my presentation about .NET interoperability, then there are a couple of demos I couldn’t deliver due to time constraints, and I promised to blog it. So, here we go.

It’s about streams. You already know that in NAV there are two data types, InStream and OutStream, that allow you to stream data in and out of generic sources or destinations. They are a fantastic tool, because they require you to know nothing about the type of source or destination, and you can store and retrieve data without having to care if the data comes from Internet, or a BLOB field, or is it written to a file, or transported over an XMLport. Stream makes it abstract and allows you to simply handle the data, and make the object itself care about the specifics.

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