I'm building a Slack application/bot and I want it to be able to welcome user every time one starts a direct message conversation with it.
For that purpose, I set up my Slack application accordingly with the documentation in order to be able to receive the 'im_created' event. Especially, I added the im:read bot scope (and even the im:read workspace scope, just to make sure) and subscribe to this event. But I never received it whereas I could receive all other type of events I needed.
Has someone already been in this case and share with me what I'm missing here ?
The 'im_created' event should not be relied upon, at least on small workspace. Indeed, this what the Slack support person answered to my request:
"I was initially testing on a workspace that had a lot of users. Then I decided to test on a smaller workspace and there, I was able to replicate what you were seeing. Turns out that on smaller workspace when a user joins the workspace, we automatically open DMs with between that user and about 10 other users. So it's possible that the DM channels with your bot already existed because they were created as soon as the user was added to the workspace, hence no im_created events.
I tested some more by inviting new users to my small workspace while listening to the im_created event subscribed at a workspace level (not a bot level). As soon as the new user accessed the workspace what do you know? An im_created event is fired. However, this doesn't work if you subscribe at a bot level."
For this use case (welcoming user when starting conversation with the bot), one should use 'app_home_oppened' event and test if it is the beginning of the conversation with your own backend/data, quoting again the Slack support :
"Any way you cut it, this would not have been the right event for your user case, app_home_opened is the right call."
The CloudKit WWDC videos recommend implementing sync like this:
Track local changes
Send changes to the server
Resolve conflicts
Fetch server changes with CKFetchRecordChangesOperation
Apply server changes
Save server change token
I'm following this pattern in my app, but I'm running into a problem with deletion and parent-child relationships.
Let's say we have a list of books that are split up into categories. Every book has to belong to exactly one category.
I start with data like this:
SERVER
Thrillers: "Look Out!", "Secret Spy"
Non-Fiction: "Sailing the Seas", "Gardening Adventures"
Computer Programming: <empty>
As you can see, the final category is empty. Let's say I have two devices with exact copies of this data.
Now, on Device 1, the user adds a book CloudKit Sync to "Computer Programming":
DEVICE 1
Thrillers: "Look Out!", "Secret Spy"
Non-Fiction: "Sailing the Seas", "Gardening Adventures"
Computer Programming: "CloudKit Sync"
But on Device 2, the user completely deletes the "Computer Programming" category (it's empty, so this is fine from Device 2's point-of-view):
DEVICE 2
Thrillers: "Look Out!", "Secret Spy"
Non-Fiction: "Sailing the Seas", "Gardening Adventures"
Device 1 syncs first, so it creates a new Book entry with its parent field set to Computer Programming.
But now Device 2 starts its sync process. It applies its changes to the server, so it deletes the CKRecord corresponding to "Computer Programming". This is consistent with Device 2's worldview, where the category is empty and can be deleted.
However, when it deletes this category from the server, this doesn't make sense with respect to the worldview of Device 1 and the server itself. There's now an orphan book called CloudKit Sync that has a dangling pointer to its parent.
If I'm following Apple's recommendations from WWDC, how do I avoid this scenario? Depending on the order of the sync, I can easily arrive at an inconsistent state with an orphaned book and an invalid parent reference.
What I'd like to happen is for the Delete command from Device 2 to return an error telling me I'm going to orphan a book and prevent the action from occurring at all, so I can take some action to fix the situation.
Is that possible? Is there another way to approach this?
Yes, the behavior you want for Device 2 is possible. I see three aspects of cloudkit that will come into play in your scenario. Let's look at those first, then how they might be used in your scenario.
First, assuming that both (or all) devices have subscribed to changes to the appropriate records, each device would be notified that someone else added or removed something. The device receiving the alert would then have the opportunity to decide what to do about it. (remove it from it's local view, replace it on the server, etc)
Second, you can set the behavior for handling conflicts using the savePolicy on the CKModifyRecordOperation. You can specify whether the last change should overwrite older records, throw an error, etc. See https://developer.apple.com/documentation/cloudkit/ckrecordsavepolicy?language=objc for the three options. (I've only used this in the context of two users modifying a common record, but a deletion after another user updated the record should then throw a server record changed error).
Third, assuming you've configured the aforementioned savePolicy, is the server change token itself. I find it easiest to envision the change token as just a last-modified timestamp. "My copy of this record was last modified at 10:42pm" kind of thing. Depending on the overwrite options you've selected in the aforementioned savePolicy, the device will receive an NSError Server Record Changed alerting you that the version on the server is from, say, 10:56pm, and that your local version may no longer be valid.
The userInfo in the resulting NSError includes 3 versions of the record in question: the current version on the server, the version you tried to submit, and the common ancestor version. The guides from Apple say it's up to the developer to decide what how to merge this information. But in theory, you'd be able to diff the changes, decide which you want to keep, and then submit a new operation.
Regarding your specific scenario: Assuming you fully authorize and trust both dev1 and dev2 to delete records, then I would subscribe to creation and deletion events, and set the savePolicy to throw an error when attempting a conflicting change. In this case, Device 1 would add the record and Device 2 would receive the notification of the new record. If Device 2 simply attempts to delete the old record, it should fail with a server record changed error, which you could display to the user as
"Someone else modified this record, do you really want to delete it
(y/n)."
Device 2 would have to refresh the record (and receive the new record change token) before proceeding. After that, if Device 2 still wants to delete the new record, it could, but then Device 1 would be notified of the change via the aforementioned subscription. Device 1 would then download the new record to (or in this case remove the old record from) its local view. The subscription notification could alert user 1:
"Your record Foo was just deleted by Bar"
This will work even if the events happen practically simultaneously, because one of the changes will be applied on the server first and the other device's token will immediately become out-of-date. So, if Device 2 managed to delete the record first, Device 1's attempt to modify the record will fail with server record changed because Device 1's change token is now out of date. Device 1's error handler would have to decide whether to honor the deletion or to proceed with creating a new record based on your business rules. Maybe ask user 1 with something like:
"Computer Programming" has been removed from the server. Do you want to recreate
it?
At this point, user1 can send flame emails demanding other users stop deleting their newly created records, and user2 can demand that people stop recreating the records they just "cleaned up." :)
You could get a lot more complicated, maybe giving device 1 precedence over device 2, such that when device 1 is notified that the record is deleted, then device 1 re-writes the record to the server. If you have multiple users with deletion rights, you could determine an order of precedence and build out the appropriate error/notification handlers. However, this seems excruciating complicated and error prone. Loops that auto respond (create, delete, create, delete, create, delete) could occur. I include it only as a hypothetical example, not a recommendation!
Lastly, as a different example, my app has a different scenario. The records in my case are gaming sessions. All players need read access to the session data, but only the originator is given the option to delete the record altogether. So, you might consider whether you really authorize multiple users to delete shared records or not.
Hopefully the title is clear, I couldn't find a better name but if someone can improve it please update it, thanks.
I would like the Firebase database to write on a node if a certain condition is met. For example, if one node receives an input from a client (say an angular app) then another node in the database should write certain data, something like a callback that is fired when a node receives some data.
I know there are 4 rule types (.read .write .validate .indexOn), what I am thinking of is some kind of .callback rule that is fired and writes on a node after some other node has received an input.
Obviously this can be achieved via a server side script but Firebase is about a server-less approach so I am trying to understand what are its current limits and what I can do with it.
Thanks for your responses
firebaser here
Running the multi-location update client-side or on a server-side process that you control are currently the only ways to accomplish this.
There is currently no way to trigger updates based on modifications to the database on Firebase servers. It is no big secret that we've been working on such functionality for a while now, but we have made no announcement as to when that will be available.
Also see Can I host a listener on Firebase?, which (I realize now) is probably a duplicate.
I'm using Slack API and want to detect an event when user first joins a team but cannot find such type of event in docs.
What should I look for?
I think team_join might be the event you're looking for? Depending on whether you need to respond immediately (and the consequences of missing an event if your bot is offline), you might also consider just calling users.list periodically and comparing to the list of already-seen users.
I'm working on an app right now that lets the user create new records on a recurring basis, and lets the schedule how many days in advance they want to create those records. This will almost always take place at a time when the app is not running, so I'm exploring my options for getting the app to be woken up to create the objects. As far as I see it there are four options, one of which is probably not really an option, since I'm trying to use only CloudKit and avoid creating a server-side component.
Option 1:
Use Background fetch to periodically refresh the records and check to see if anything is changed. In this instance I would probably have some kind of CloudKit record that represented the recurrence, in addition to the record type that needs to be created. Then I can just check the recurrence object and create a new record if needed
Option 2:
Schedule a local notification when the user schedules the recurrence. I thought this was going to work, but as far as I can tell, the app will not actually be launched even if it's a silent notification, unlike remote notifications.
Option 3:
Write some code locally that will check a data structure whenever the app is launched to check to see if any new records need to be created.
Option 4:
Create a server application that will create the records for me. Like I said, not really something that I want to do, even if it's the "best" option usually.
With option 1 you can not be certain that your app is running.
Option 2 won't work. As you said the app won't be activated. Or the notification must nog be silent and the user has to select to open the app.
Option 3 is much better than 1 and 2 if you don't mind that it could happen that the records won't be created for a long time if the user never opens up your app.
Option 4 is the best option for this. you will have full control over when to add what.
But... Do you already know in front what data to add? Then why are you adding that data? Can't you just calculate it and assume it's there? Maybe even based on a settings record or so?