How to remove an array item from a nested document in firebase?

Question

I'm working on a Vue,firebase app and I'm saving the userevents in a firebase collection, I update this userevents array when a user schedule an event and want to delete it when the user cancels or remove it,

users(collection) -
 test123(document) -
      "id" . --fields
      "username" . --fields
      "userevents" . --array
         [0]
            "eventid"
            "date"
            "desc"
            "status"
         [1]
            "eventid"
            "date"
            "desc"
            "status"

From UI, if the user cancels an event, I will have the eventid and want to delete it from the userevents array. I tried removing the item from the array using below code, but it is deleting all the items from the userevents,

userRef.update({
    eventid: firebase.firestore.FieldValue.delete()
});

Is there a way to achieve this in firebase?

clk · Accepted Answer · 2019-04-29 03:33:08Z

28

Firestore currently doesn't support deleting elements from an array using just a field from an element in that array (in your case, eventid). There are a couple of workarounds:

Method 1

You can use FieldValue.arrayRemove to remove an element from an array by value. The value has to match the whole element in the array, and it will delete all elements in the array that match that value. You can read more about that, and manipulating arrays in general here. Since your array elements are objects, the code would look like this:

userRef.update({
    "userevents": firebase.firestore.FieldValue.arrayRemove({"eventid": ..., "date": ..., "desc":..., "status":...})
});

Method 2

You're currently storing objects inside of an array. What you could do is make userevents a map (an object) instead of an array. Assuming that eventid is unique, you can index the map by eventid and then just delete the entry from the map like this:

userRef.update({
    ['userevents.' + eventid]: firebase.firestore.FieldValue.delete()
});

edited Apr 29, 2019 at 3:33

answered Apr 26, 2019 at 23:38

clk

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5 Comments

Annette Over a year ago

i tried your method2 , but it is not deleting the key from the userevents map. I think the eventid is considered as string and not as variable as per the above syntax, userRef.update({ "userevents.${eventid}": firebase.firestore.FieldValue.delete() });

clk Over a year ago

Sorry, this should work: userRef.update({ ['userevents.' + eventid]: firebase.firestore.FieldValue.delete() }); I'll update the answer as well

secretshardul Over a year ago

Another option would be to read the array from Firestore, delete the item from a certain index and then write the updated item.

iCantC Over a year ago

Assume if the values in the array are of type double, then FieldValue.arrayRemove has to match the entire double value up to last precision, this is pain. I demand, delete by index.

Paul Over a year ago

2022 Cloud Update: Note that the import changed to FirebaseFirestore.FieldValue.arrayRemove({});

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