CODEWITHSUNDEEP
firebasefirebase-realtime-database
kierandes
kierandes

Reputation: 181

Update A Firebase node with a Snapshot data without overwriting Data

I'm looking at synching a node e.g. /a/b/c with node /data/c

There is data at node /a/b/c - so I just want to grab a snapshot of /data/c and put that data in to /a/b/c without deleting existing values.

Would an approach like :

Ref.update({
                                snapshotdata.val()
                            }).key;

Would this work? I'm not sure how firebase would parse the snapshot, if it takes the whole thing and overwrites or it would take individual values and adds.

Thanks in advance for any clarity.

Best Regards, Kieran

Upvotes: 0

Views: 473

Answers (1)

Michael Bleigh
Michael Bleigh

Reputation: 26313

It depends. Snapshot values are simply JSON objects (or primitives, depending on the node). update() will replace any nodes specified by the keys in the update, but not any that aren't. So if /a/b/c looks like:

{
  name: 'old name',
  data: {
    gonnabe: 'gone'
  },
  created: 12345679
}

and data/c looks like:

{
  name: 'new name',
  data: {
    nested: true
  },
  updated: 12345679
}

doing an db.ref('a/b/c').update(dataSnapshot.val()) will result in:

{
  name: 'new name',
  data: {
    nested: true
  },
  created: 12345679,
  updated: 12345679
}

Note that the nested field in data was wiped out by the update, but the non-nested field created was not.

If you want to do deep updates, you'll need to construct an update with slash-delimited fields for each deep node you want to update. So instead of the above, you might have:

{
  "name": "new name",
  "data/nested": true,
  "updated" 12345679
}

This will be non-destructive to the nested data and only update values that are directly referenced, resulting in:

{
  name: 'new name',
  data: {
    gonnabe: 'gone',
    nested: true
  },
  created: 12345679,
  updated: 12345679
}

Hope that helps!

Upvotes: 3

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