System.DBNull.Value is not available

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Posted on by psined

As part of integration with another system I use System.Data.SqlClient library to create a command object and pass parameters on to it. One of the parameters every once in a while will get a DBNull.Value. It seems that AX does not offer a way to make static get_Value() call directly on the DBNull type. So the code like this won't compile:

System.DBNull nullValue = System.DBNull::get_Value();

Any idea how else I can do what I need?

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Vilmos Kintera 46,149 on at

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AX does not use SQL Server's null values in the fields, it is always an empty string, 0, or 1900-01-01 00:00 for dates, etc.

msdn.microsoft.com/.../aa846236.aspx

You could use the Global class for getting the null value as a proxy class/business connector call from AX.

msdn.microsoft.com/.../global.nullvalue.aspx

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psined on at

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Hi, thanks for quick response.

I fully understand that AX built-in string type cannot take a null value rather than an empty string. The behavior I need though is to pass DBNull.Value object to one of the required System.Data.SqlClient.SqlParameter instance whenever the source X++ string is empty. The SQL parameter is required, so I must pass it a value, it's just at times the value needs to be DBNull.Value. This can be easily achieved and is a normal practice in C#.

Not sure I understand how I could use Global::nullValue(<type>), nor ClrInterop::Null(<type>) here. DBNull.Value is not the same as Global::nullValue("System.DBNull") if that is what you mean.

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Vilmos Kintera 46,149 on at

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Am I understanding right that you use reflection to use the .Net SQL namespaces to write code inside AX?

Maybe you could just write the whole logic in a C# project as a wrapper which could handle your DBNull value correctly, do the calculations or whatever you would like to use there, and pass the end result back to AX for further processing.

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psined on at

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Thanks Vilmos.

Well, I guess it kinda fits between AX and .Net. I'm making calls to CLR objects from within X++ so this obviously circles into the CLR interop topic. It seems that marshaling in CLR interop for AX R3 is a little quirky - my other thread on the System.Double type interop from X++ code adds to that.

I'll wait for other opinions. Meantime I'll think of a workaround on the SQL side of things, such as NULLIF() function and such...

Thanks for your help again!

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Martin Dráb 237,801 Most Valuable Professional on at

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It seems that .NET Interop from X++ doesn't support static properties.

Consider creating a C# project in AOT and write most code using .NET types in C#, which will help you to avoid all such issues and allow you to use all C# features. I tend to use it for every time when I need more than just a few lines of code with .NET types.

Things like nullValue() aren't going to help, because what Value returns is an object instance, not a null reference or a default value in any way.

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psined on at

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OK, that's what I thought. Thanks Martin.

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