CODEWITHSUNDEEP
node.jsfirebasefirebase-realtime-databasegoogle-cloud-functions
Bbx
Bbx

Reputation: 3384

In a Firebase Database Cloud Function, how can you add/replace an item in a list

My database structure is:

- Scores
    - r5rwuerpepdsoazdf (user UID)
        - scoreString: "5,12"
    - j6fdasdfsdfs08fdd
        - scoreString: "1,4,7"

and I have a cloud function that updates the Score for a particular user UID when a value is written in another node (ScoreStacks):

exports.updateScoreString = 
functions.database.ref('/ScoreStacks/{uid}/{levelKey}/Score')
  .onWrite((dataSnapshot, context) => {
  const score = dataSnapshot.after.val();
  const scoreStringRef = dataSnapshot.after.ref.root.child('Scores/' + context.params.uid + '/scoreString');
  return scoreStringRef.transaction(scoreString => {
    if (!scoreString) // transactions return null first time
    {
      return scoreString;
    }
    return scoreStringWithAddedScore(scoreString, score);
  });
});

This is all working fine apart from if the UID in the Scores node does not yet exist. Then nothing happens. I guess that is fair enough because scoreStringRef is refering to a path that doesn't exist.

So how can I ensure a new entry is made in the Scores node if the UID does not exist yet? It all has to be done atomically.

Upvotes: 0

Views: 98

Answers (1)

Frank van Puffelen
Frank van Puffelen

Reputation: 598728

It's hard to be sure without seeing scoreStringWithAddedScore, but I suspect you want this:

  return scoreStringRef.transaction(scoreString => {
    if (!scoreString) // transactions return null first time
    {
      scoreString = "";
    }
    return scoreStringWithAddedScore(scoreString, score);
  });

A more concise (but somewhat harder to parse if you're new to this) version:

  return scoreStringRef.transaction(scoreString => {
    return scoreStringWithAddedScore(scoreString || "", score);
  });

Upvotes: 1

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