Removing specific map/object from array in firebase

Question

I'm experimenting with arrays and maps/objects in firestore. I wondered how can I remove a specific map from the array. I tried something like this:

await Firestore.instance.collection('users').document(interestedInID).get().then((val){
  return val.data['usersInterested'].removeWhere((item)=>
    item['userID'] == userID
  ); 
}).catchError((e){
  print(e);
});

but I get this error in terminal:

Unsupported operation: Cannot remove from a fixed-length list

I don't really understand what it means. I did some googling and fixed-length list is exactly what it says. It's a list that has a fixed length and it can't be changed, but fixed-length list has to be declared explicitly. Growable list on the other hand doesn't need to be declared. I haven't declared the fixed-length list in my firestore, yet it keeps saying that I can't remove elements from it. I can add / push elements however and remove them using:

'key': FieldValue.arrayRemove([value])

but I can't figure out how to remove the element based on a specific condition. In this case an userID.

Any suggestions? Thanks a lot!

Hi @Andrey. Was quite a long time ago, but I posted the solution that worked for me, but it showed I deleted it. I don't know why, so I undeleted the post. Can you see it underneath? — Lukas Luke Stateczny
– Lukas Luke Stateczny, Commented May 4, 2020 at 22:39

Lukas Luke Stateczny · Accepted Answer · 2019-01-29 15:31:48Z

1

Figured it out.

await Firestore.instance.collection('users').document(interestedInID).updateData({
  'usersInterested': FieldValue.arrayRemove([{}.remove(userID)])
});

I'm not sure, but I think get() simply allows you to read the document, but doesn't allow to make any changes to it. Anyways, now it works

answered Jan 29, 2019 at 15:31

Lukas Luke Stateczny

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Comments

Sven · Accepted Answer · 2019-03-01 13:26:46Z

0

This may be a workaround:

You fetch your specific Array with key: values from Firebase
Put that in a temporary reference List in dart
Remove your specific Map from the reference List, like you did before
Update data in Firebase like so:

// make a reference List
List<Map> _modifiedUsersInterested = List();

// ... (fetch your Array first from Firebase, put those items in the reference List)

// remove the right Map from the reference List
_modifiedUsersInterested.removeWhere((item) => {
    item['userID'] == userID
});

// set the reference List as your array in Firebase
await Firestore.instance
.collection('users')
.document(interestedInId)
.updateData(
    {'usersInterested': _modifiedUsersInterested}
);

answered Mar 1, 2019 at 13:26

Sven

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1 Comment

Axes Grinds Over a year ago

did you actually confirm that this method works? Either way, there should be a much simpler way to do this without reading and then resaving the entire list minus the removed value.

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