set('key', undefined) in Cloud Code does not result in key being undefined in beforeSave

[airdrummingfool]

Saving an object after calling set('key', undefined) does not result in key being undefined in beforeSave. Once beforeSave has completed and the save call returns, key is undefined as expected.

This might be related to #1840. Test incoming.

[flovilmart]

When not providing any value, the JS-SDK will interpolate it as a no-op as this is equivalent as calling set('key'). A missing argument will be set to undefined.

[airdrummingfool]

@flovilmart I'm not sure I understand. As the test in my PR shows, calling object.set('key', undefined) does eventually set key to undefined, it just doesn't take affect until after beforeSave is executed, which is inconsistent with seting keys to other (non-undefined) values. This assumes key was previously not undefined, otherwise yes, seting an undefined value to undefined would be a no-op (I should have made that clear in the issue description, sorry).

e.g.:

1. Create TestObject, set 'key' to 'hello' using set('key', 'hello');
2. Save TestObject. In beforeSave, log value of key (output is "hello", as expected).
3. Set 'key' to undefined, using set('key', undefined);
4. Save TestObject again. In beforeSave, log value of key. Expected output is undefined, but actual output is "hello".
5. Once save is complete, log value of key again. Value is now undefined as expected.

[flovilmart]

The main issue is that undefined is not serializable, so anything that gets set to undefined server side can't be forwarded to the client, unless a fetch is done.

[airdrummingfool]

It still affects Cloud Code functions that modify and then return an object (i.e. most things not the result of a client-side save() call), right? Or is seting a key to undefined not supported, and instead we should use unset()?

[flovilmart]

You should use unset, and unset itself is broken, as you noticed. I've opened PR on the iOS and JS SDK's to improve that.

[airdrummingfool]

Great, thanks for the clarifications.

[drbarto]

@flovilmart I maybe have a problem that is related to the mentioned brokenness of unset. What's the status of your PR, can you please post a link?