I am trying to remove all the children under a node. Is there a way to delete all the items under a node? The structure is like:
lastMessages
- mainId
- timestampedId
- keys:values
What I want to do is, by using mainId, delete all the items under it. Actually there's only one timestampedId at a time as this is for lastMessages. That's why I thought I should delete all items under mainId just before writing my new value. Is there a way to achieve that; or is there any better ways than I thought?
let ref = Firebase(url: path)
let myRef = ref.childByAppendingPath(mainId)
// how to delete all items under myRef?
Simply call myRef.removeValue()
Explained in the docs
The simplest way to delete data is to call removeValue on a reference to the location of that data.
Related
I have a SwiftUI calendaring app with a UI similar to the built-in Calendar.app. I'm getting crashes whenever I try to delete events. The overall lifecycle of my app is as follows:
Download calendar data from server and populate models ([Events], [Users], [Responses] etc)
Transform the source data into a more structured format (see https://stackoverflow.com/a/58583601/2282313)
Render list view of events, each event linking to a Detail View and an Edit modal (very similar to calendar.app)
When an event is deleted, I tell the server to delete the event (if it's a recurring event, the server will delete multiple events), then refresh my data from the server by re-downloading the data, re-populating the models and re-generating the structured data (which causes the list to refresh).
When I do this, I get crashes coming from my calculated values because event data displayed in the detail view is no longer available. For example, I get the array index of a user's RSVP as follows:
var responseIndex: Int {
userData.responses.firstIndex(where: { $0.user == response.user && $0.occurrence == response.occurrence })!
}
I thought this was because I hadn't dismissed the view displaying the deleted event before updating the data, but even if I delay the data refresh until the view is no longer displayed, I still get the crash (SwiftUI seems to keep these views in memory).
What is the right way to handle data deletion? Do I need to keep deleted events in my UserData EnvironmentObject and just mark them as "deleted/hidden" to avoid this issue, or is there a better way to handle it?
There's quite a bit of code involved in this, so it's tricky to provide a sample I'm happy to add relevant bits if asked.
EDIT: I found this article which clarifies something really well: https://jasonzurita.com/swiftui-if-statement/
SwiftUI is perfectly happy to try and render nil views, it just draws nothing. Counter-intuitively, a good way to avoid crashes and make the compiler happy is to set your code up around this.
Original "answer" follows...
I don't know if this is the "right" way to do this, but I ended up making sure that none of my UserData is ever deleted to avoid the crashes. I added a "deleted" bool to my Occurrence (i.e. Event) object, and when I refresh my structured data, I get the latest data from the server, but check to see if any of the old ones are no longer present. Steps are:
Get latest list of occurrences from server
Create a second init() for my structured data which takes the existing data as an argument
Inside the new init(), flatten the structured data, check for deleted items against the new data, update data which hasn't been removed, cull duplicates, then merge in net new data. Once that's done, I call my original init() with the modified data to create new structured data
Code looks like this:
init(occurrences: [Occurrence], existing: [Day]) {
// Create a mutable copy of occurrences (useful so I can delete duplicates)
var occurrences = occurrences
// Flatten the structured data into a plan array of occurrences again
var existingOccurrences = existing.compactMap({ $0.occurrences }).flatMap { $0 }
// Go through existing occurrences and see if they still exist.
existingOccurrences = existingOccurrences.map {
occurrence -> Occurrence in
let occurrenceIndex: Int? = occurrences.firstIndex(where: { $0.id == occurrence.id })
// If the occurrence no longer exists, mark it as "deleted" in the original data
if occurrenceIndex == nil {
var newOccurrence = occurrence
newOccurrence.deleted = true
return newOccurrence
// If it still exists, replace the existing copy with the new copy
// (in case it has changed since the last pull from the server)
// Remove the event from the "new" data so you don't get duplicates
} else {
let newOccurrence = occurrences[occurrenceIndex!]
occurrences.remove(at: occurrenceIndex!)
return newOccurrence
}
}
// Merge the existing data (with deleted items marked) and the updated data (with deleted items removed)
let finalOccurrences = existingOccurrences + occurrences
// Re-initialize the strutured data with the new array of data
self = EventData(occurrences: finalOccurrences)
}
Once this was done, I had to update my code to make sure I'm always using my structured data as the source of truth (which I wasn't doing before because accessing the "source" flat data was often easier, and I've updated my ForEach in my list view to only render a row if deleted is false.
It works! It's perhaps a sub-optimal way to solve the problem, but no more crashes. Still interested to hear better ways to solve the problem.
How I could append an element to an array like that:
Using this code I'm overriding the old data:
let toUpdate = [book.id]
self.refUsers.child(localUser.key!).child("booksPurchased").setValue(toUpdate, withCompletionBlock: { (error, _) in
You could use this method: firebase.firestore.FieldValue.arrayUnion()
Example with angularfire2:
this.afs.collection('collection').doc(id).update( {
array: firebase.firestore.FieldValue.arrayUnion( 'newItem' )
});
For more information: https://firebase.google.com/docs/reference/js/firebase.firestore.FieldValue#arrayunion
In this case, you will have to read the existing data, then write it back with the new value added. Arrays like this are not always the best way to store lists of data if you want to perform a lot of append operations. For that, you're better off pushing data into a location using childByAutoId.
Reading and writing lists
Append to a list of data
Use the childByAutoId method to append data to a list in multiuser applications. The childByAutoId method generates a unique key every time a new child is added to the specified Firebase reference. By using these auto-generated keys for each new element in the list, several clients can add children to the same location at the same time without write conflicts. The unique key generated by childByAutoId is based on a timestamp, so list items are automatically ordered chronologically.
You can use the reference to the new data returned by the childByAutoId method to get the value of the child's auto-generated key or set data for the child. Calling getKey on a childByAutoId reference returns the auto-generated key.
You can use these auto-generated keys to simplify flattening your data structure. For more information, see the data fan-out example.
-https://firebase.google.com/docs/database/ios/lists-of-data
You could set the values of the keys in the array to true, and then set the value directly in an update.
So if 'newId' is the new item to add, maybe something like:
const update = {
[`/users/${localUser.key}/booksPurchased/${newId}`]: true]
}
firebase.db.ref().update(update);
Firebase docs example of an update:
https://firebase.google.com/docs/database/web/read-and-write
I'd like to write a function to remove an entire child from Firebase. I'm using XCode 10 and swift 3+.
I have all the user info of the child I'd like to delete so I assume the best call would be to iterate through every child and test for the matching sub child value but it would be great if there was a faster way.
Thanks for the help!
Heres what I'd like to delete
I assume testing for epoch time then removing the whole node would be ideal. Also not sure how to do this
I understand you don't have access to the key of the node you want do delete. Is that right? Why not? If you use the "observe()" function on a FIRDatabaseQuery object, each returned object should come with a key and a value.
Having a key it is easy to remove a node, as stated in the Firebase official guides.
From the linked guide,
Delete data
The simplest way to delete data is to call removeValue on a reference
to the location of that data.
You can also delete by specifying nil as the value for another write
operation such as setValue or updateChildValues. You can use this
technique with updateChildValues to delete multiple children in a
single API call.
So, you could try:
FirebaseDatabase.Database.database().reference(withPath: "Forum").child(key).removeValue()
or
FirebaseDatabase.Database.database().reference(withPath: "Forum").child(key).setValue(nil)
If you can't get the key in any way, what you said about "iterating" through the children of the node could be done by using a query. Here's some example code, supposing you want all forum posts by Jonahelbaz:
return FirebaseDatabase.Database.database().reference(withPath: "Forum").queryOrdered(byChild: "username").queryEqual(toValue: "Jonahelbaz").observe(.value, with: { (snapshot) in
if let forumPosts = snapshot.value as? [String: [String: AnyObject]] {
for (key, _) in forumPosts {
FirebaseDatabase.Database.database().reference(withPath: "Forum").child(key).removeValue()
}
}
})
Here you create a sorted query using as reference "username" then you ask only for the forum posts where "username" are equal to Johanelbaz. You know the returned snapshot is an Array, so now you iterate through the array and use the keys for deleting the nodes.
This way of deleting isn't very good because you might get several posts with the same username and would delete them all. The ideal case would be to obtain the exact key of the forum post you want to delete.
When I call this observe function from in my viewcontroller, the .childadded immediately returns a object that was already stored instead of has just bin added like .childadded would suspect.
func observe(callback: RiderVC){
let ref = DBProvider.Instance.dbRef.child("rideRequests")
ref.observe(DataEventType.childAdded) { (snapshot: DataSnapshot) in
if let data = snapshot.value as? NSDictionary {
let drive = cabRide(ritID: ritID, bestemming: bestemming,
vanafLocatie: vanaf, taxiID: taxiID, status: status)
print(drive)
callback.alertForARide(title: "Wilt u deze rit krijgen?", message: "Van: \(vanaf), Naar: \(bestemming)", ritID: ritID)
}
}
}
When I try this function with .childchanged, I only get a alert when it is changed like it suppose to do, but when doing .chiladded, it just gets all the requests out of the database and those requests were already there.
When I add a new request, it also gives an alert. So it works, but how can I get rid of the not added and already there requests?
Does anybody know this flaw?
This is working exactly as promised. From the documentation:
Retrieve lists of items or listen for additions to a list of items.
This event is triggered once for each existing child and then again
every time a new child is added to the specified path. The listener is
passed a snapshot containing the new child's data.
That might seem weird at first, but this is generally what most developers want, as it's basically a way of asking for all data from a particular branch in the database, even if new items get added to it in the future.
If you want it to work the way you're describing, where you're only getting new items in the database after your app has started up, you'll need to do a little bit of work yourself. First, you'll want to add timestamps to the objects you're adding to the database. Then you'll want to do some kind of call where you're asking to query your database by those timestamps. It'll probably look something like this:
myDatabaseRef.queryOrdered(byChild: "myTimestamp").queryStarting(atValue: <currentTimestamp>)
Good luck!
The way I set up my database structure was like this:
It starts with Lists then there is a child that shows the users UID then inside that there is one item.
The one item inside the UID gets updated every time I attempt to save new data. Instead of adding another item the same one just keeps changing. I was wondering how I could instead of update the same one item every time add more items.
The way that I save my data is with this line of code.
let user = FIRAuth.auth()?.currentUser
let item: String = self.ItemTextField.text!
self.ref.child("Lists").child(user!.uid).setValue(["Items": item])
More idiomatic is to store the list of items with so-called push ids:
Lists
twEymn...
-Km....: "Yoghurt"
You'd do this with:
self.ref.child("Lists").child(user!.uid).childByAutoId().setValue(item)
The childByAutoId() generates a unique, sequential ID. It's similar to an array index, but this one works reliably in multi-user environments and when users can be offline. Read this blog post about these so-called push ids.
Alternatively you can use the name of the item as the key (if the item has to be unique in the list):
Lists
twEymn...
"Yoghurt": true
In that case the code becomes:
self.ref.child("Lists").child(user!.uid).child(item).setValue(true)
One thing you'll note is that both of these approaches only deal with the newly added item, instead of the list of items as a whole. This is a general pattern you'll see when using Firebase. By isolating your modifications, your app will be more scalable without users getting into each other's way.
The problem is that you are setting a key-value pair ("Items" : item) so that each time it is updating the value for the same key. What you could do instead is ("Items" : [your array of items here]), which will update a list of items for the same key each time.
You could also fetch the current list of items, append your new item locally, and then update.