Firestore transaction sequential creation of collections and updating of documents-CodePudding

Enviroment: nodejs, firebase-admin, firestore.

Database scructure (space):

Database scructure (user):

Creating new space (example):

// init data
const userId = "someUserId";
// Create new space
const spaceRef = await db.collection("spaces").add({ name: "SomeName" });
// Get spaceId
spaceId = spaceRef.id;
// Get user Doc for upate their spaces
const userRef = await db.collection("users").doc(userId);
// Add "spaceId" to user spaces list
userRef.collection("spaces").doc(spaceId).set({ some: "data" });
// Create collection "members" in new space with "userId"
spaceRef.collection("members").doc(userId).set({role: "OWNER"})

Question: I want to execute this code inside single runTransaction, but as I see transactions support only one-time read and multiple update, this does not suit me, since I get the spaceId I need during the execution of the code.

Why I want to use transaction: In my data structure, the relationship between the created space and the presence of the ID of this space on the user is required. If we assume that an error occurred during the execution of this code, for example, the space was created, but this space was not added inside the user profile, then this will be a fatal problem in my database structure.

Similar to other databases, transactions solve this problem, but I can't figure out how to do it with firestore.

Maybe you know a better way to protect yourself from consistent data in this case?

CodePudding user response：

Actually, you don't need a Transaction for that, since you are not reading documents.

With db.collection("users").doc(userId); you are actually not reading a document, just calling "locally" the doc() method to create a DocumentReference. This method is not asynchronous, therefore you don't need to use await. To read the doc, you would use the asynchronous get() method.

So, using a batched write, which atomically commits all pending write operations to the database, will do the trick:

  const userId = 'someUserId';
  const userRef = db.collection('users').doc(userId);

  const spaceRef = firestore.collection('spaces').doc();
  const spaceId = spaceRef.id;

  const writeBatch = firestore.batch();
  writeBatch.set(spaceRef, { name: "SomeName" });
  writeBatch.set(userRef.collection("spaces").doc(spaceId), { some: "data" });
  writeBatch.set(spaceRef.collection("members").doc(userId), {role: "OWNER"});

  await writeBatch.commit();

You should include this code in a try/catch block and if the batch commit fails you will be able to handle this situation in the catch block, knowing that none of the write were committed.