CODEWITHSUNDEEP
javascriptnode.jsfirebase-realtime-databasetransactionsgoogle-cloud-functions
Aliton Oliveira
Aliton Oliveira

Reputation: 1339

Cloud Functions: Realtime Database transaction not working with condition

I am trying to decrease the field amount which represents the amount of products available for sale.

My database is structured like below:

- Stock
 - StoreId
  - DepartmentId
   - ProductId
    + price
    + amount

My storeId has a fixed value and I am only looping through the variables DepartmentId and ProductId.

Below is how I created a node array or children array for the transaction:

  const childArray = [];
  depIds.forEach(depId => {
    const prodIds = groupedProducts[depId].reduce((acc, val) => [...acc, val.prodId], []);
    prodIds.forEach(prodId => {

      childArray.push(admin.database().ref("Stock")
        .child(storeId)
        .child(depId)
        .child(prodId)
        .child("amount")
        .once('value'));
    });
  });

When I add the condition: amount > 0, nothing happens. It only works when I remove the condition.

const snapshots = await Promise.all(childArray);
snapshots.forEach(snapshot => {
  snapshot.ref.transaction(amount => {
    //if (amount) return amount + admin.database.ServerValue.increment(-1);
    if (amount > 0) return amount - 1;
        
  })
})

Furthermore, what I really need is to compare the amount in the database with the amount coming from the request (let's call it qty)

For this, I would have to retrieve the current path for productId and departmentId. But as showed below, snapshot.ref.parent does not return the path.

snapshots.forEach(snapshot => {
  snapshot.ref.transaction(amount => {
    //if (amount > 0 & amount >= qty) return amount + admin.database.ServerValue.increment(-qty);

    const productPath = snapshot.ref.parent;
    const departmentPath = snapshot.ref.parent.parent;
    // Get qty based on productPath and departmentPath
    if (amount > 0 & amount >= qty) return amount - qty;
        
  })
})

So, I have three questions:

  1. How to retrieve the current paths for departmentId and productId
  2. How to update the field amount based on a condition and abort the whole transaction if any condition is not satisfied
  3. How to make admin.database.ServerValue.increment(-qty) work

I appreciate any help!

Upvotes: 0

Views: 136

Answers (1)

Frank van Puffelen
Frank van Puffelen

Reputation: 598718

You don't need a transaction for this. Instead, once you know the full path of the node(s) to update, you can use increment() and then use security rules to validate that the value doesn't go below 0.

So in code that'd be:

admin.database().ref("Stock")
  .child(storeId)
  .child(depId)
  .child(prodId)
  .update({ "amount", admin.database.ServerValue.increment(-1));

And then in the rules:

{
  "rules": {
    "Stock": {
      "$storeId": {
        "$depId": {
          "$prodId": {
            "amount": {
              ".validate": "newData.val() >= 0"
            }
          }
        }
      }
    }
  }
}

Upvotes: 1

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