Forward Migration

[Anonymous]

Please can someone offer me some insight into how Forward Migration works and how to code it.
I have looked into it in the GDL reference Guide but can't really make out how to go about it.

Any help will be greatly appreciated.
Kind regards,

[Anonymous]

So essentially what I need to know is, when creating an object that will be updated down the line, do I need to do anything, do I need to Set a GUID or is that automatic and if so, how do I do it.

Sorry if this is a simple and annoying question but I am struggling here.
Thanks again.

[James Murray]

No I wouldn't call it simple. On the contrary it's pretty advanced and doesn't concern most users, even most GDL people, judging by the very thin Google results, where your post was the top item.

Have you learned anything? I am just starting to look at this. I'm going to try to find some AC objects that have the Forward and Backward scripts and see what I can find out.

[Barry Kelly]

If you are modifying an object and doing a simple 'Save' so it has the same name and GUID then there should be no problem when you update this object.
Of course that depends on what you have changed in your scripts as to how it affects existing object instances.

If however you create a new object so it has a new GUID then this is when you can use the Forward Migration.
I don't know exactly how it works as I haven't used it but my understanding is that you can tell the new object to set parameters based on the values of the parameters in the old object. These parameters can be the same names or can be completely different - you can even base new parameter settings on combinations of old parameters.
It will then replace the old object with the new object.

I believe Graphisoft have used it when amalgamating something like multiple single door objects into a single door object with multiple options. I'm not 100% sure on this as I don't use their library.
But if you look in one of the Migration libraries you should find some examples.

Barry.

[James Murray]

That's a good summary, based on what I've learned. If you are careful with the GUIDs then you don't need it. The two cases it's needed are "un-forking" multiple objects into one, and handling new parameters where the default values wouldn't be acceptable in old instances.

The syntax of the script itself, combined with the thin explanation in the manual, makes for a challenging topic, but I've made some progress. I would like to use it to get rid of the old markers in the marker choosers.

[Laszlo Nagy]

Hi James, it is great to see you here again. You have not posted in almost 5 years. People on the Forum are to this day turning to your blog posts for AC info.
Are you back for good?

[James Murray]

I have questions, you have answers! Thank you Laszlo.

[Laszlo Nagy]

Seems to me you too have quite a few answers on that blog.