Firestore transaction with multiple get

Question

I\'m trying to run a transaction with a variable number of read operations. I put the read () operations before than update ().

Reading the Firestore doc on https://clou

Answer 1

I couldn't figure out how to do this in pure Typescript, but I was able to find a JavaScript example that uses promises, so I adapted that to fit my needs. It seems to be working correctly, however when I run my function rapidly (by clicking on a button in rapid succession) I get console errors that read POST https://firestore.googleapis.com/v1beta1/projects/myprojectname/databases/(default)/documents:commit 400 (). I am unclear on whether those are errors I should be worried about, or if they're simply a a result of the transaction retrying. I posted my own question about that, and am hopeful to get some answers on it. In the meantime, here is the code that I came up with:

async vote(username, recipeId, direction) {

  let value;

  if ( direction == 'up' ) {
    value = 1;
  }

  if ( direction == 'down' ) {
    value = -1;
  }

  // assemble vote object to be recorded in votes collection
  const voteObj: Vote = { username: username, recipeId: recipeId , value: value };

  // get references to both vote and recipe documents
  const voteDocRef = this.afs.doc(`votes/${username}_${recipeId}`).ref;
  const recipeDocRef = this.afs.doc('recipes/' + recipeId).ref;

  await this.afs.firestore.runTransaction( async t => {

    const voteDoc = await t.get(voteDocRef);
    const recipeDoc = await t.get(recipeDocRef);
    const currentRecipeScore = await recipeDoc.get('score');

    if (!voteDoc.exists) {

      // This is a new vote, so add it to the votes collection
      // and apply its value to the recipe's score
      t.set(voteDocRef, voteObj);
      t.update(recipeDocRef, { score: (currentRecipeScore + value) });

    } else {

      const voteData = voteDoc.data();

      if ( voteData.value == value ) {

        // existing vote is the same as the button that was pressed, so delete
        // the vote document and revert the vote from the recipe's score
        t.delete(voteDocRef);
        t.update(recipeDocRef, { score: (currentRecipeScore - value) });

      } else {

        // existing vote is the opposite of the one pressed, so update the
        // vote doc, then apply it to the recipe's score by doubling it.
        // For example, if the current score is 1 and the user reverses their
        // +1 vote by pressing -1, we apply -2 so the score will become -1.
        t.set(voteDocRef, voteObj);
        t.update(recipeDocRef, { score: (currentRecipeScore + (value*2))});
      }

    }

    return Promise.resolve(true);

  });

}