How To Use the SysPackExtension Class to Pack Additional Fields in Dynamics 365 Finance and Operations

By Elliot Thompson | December 21, 2023

If you are working with x++ development language in Dynamics 365 Finance and Operations and need to extend a class that implements packing to pack some additional fields, you might be wondering how to do it safely.

In this blog post, I will show you how to use the SysPackExtension class to achieve this.

The SysPackExtension class is a helper class that allows you to add fields to a packed class without modifying the original class. It works by utilizing the chain of command on the pack and unpack methods to add to the packed container a container of your fields where the first elements in the container are the version and the name of your extension class.

For example, the original container could look like [1, 2, 3] and you want to add 4 to that. The result would be something like [1, 2, 3, [1, “SomeBaseClass_Extension”, 4]].

Here is an example:


internal final class SSISalesOrderCopyingContract_Extension 


    public NoYes createNewOrder; 

    public int newOrdersToCreate; 


    #define.CurrentVersion(1) // same as base class 







    public container pack() 


        container retContainer = next pack(); 

        container conValues = [#CurrentVersion, #CurrentList]; 


        return SysPackExtensions::appendExtension(retContainer, classStr(SSISalesOrderCopyingContract_Extension), conValues); 



    public boolean unpack(container _packedClass) 


        boolean retValue = next unpack(_packedClass); 




            container packedExtension = SysPackExtensions::findExtension(_packedClass, classStr(SSISalesOrderCopyingContract_Extension)); 


            if(conLen(packedExtension) > 0) 


                Integer version = RunBase::getVersion(packedExtension); 



                    case #CurrentVersion: 

                        [version, #CurrentList] = packedExtension; 


    retValue = false; 





        return retValue; 



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