Updating Type without losing data

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1

Good afternoon, I need to add a property to my fantasy teams type and I don’t want to lose all my data (again).

Is there a documented procedure I can follow to add a property and ensure nothing is lost in the pre and post upgrade process?

Any help would be greatly appreciated.

James

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2

Instead of trying to upgrade and keep the data, should I just back it up and recreate it after it’s deleted?

3

I would say yes. There is no specific way defined for this. I usually do this by backing up data in stable variable and then reassigning the values from back up data to original structures.

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4

Thank you for confirming sir.

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5

@jamesbeadle,

I am guessing you are using Motoko, and in that case you are stuck with pre-upgrade, and post-upgrade methods to ensure you keep the data.

Rust has two libraries that make you able to persist data without pre-and-post upgrade calls, but the learning curve to master Rust on the IC is much higher than the one for Motoko.

So, I have some good news for you that may be useful there is a library that can persist data even if you use Motoko, if you haven’t see it is called Motoko-Hash-Map by @ZhenyaUsenko:

It works very well, and I do recommend it.

Let me know about your fantasy game, sounds fun!

Joseph

6

If you’re changing the types and they’re not backward compatible (you can use didc to compare the old and new candid, see here: https://internetcomputer.org/docs/current/motoko/main/upgrades/#upgrade-safety ), then you can migrate the old data when reloading it in postupgrade:

Write a function that maps the old type to new and pass the data through this in postupgrade. Then remove this function for future upgrades since you wouldn’t need it again.

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