Question 119079 in Firebase Question posted in
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Firebase – Issue with setDoc() and updateDoc() when using "if" "else"

I have this issue and can’t figure out how to solve it, addDoc() and setDoc() functions separately without using "if" "else" work correctly, but when I use "if" "else" it gives me this error.

"Error adding product to cart: TypeError: Cannot read properties of undefined (reading ‘quantity’)"

It is a function to add a product to the cart, it must check if the document is already in the subcollection, then increase quantity +1, otherwise create a document, taking the name of the product as the document id.

I’am using Vue.js 3 and Firebase 9.

const productRef = doc(db, "carts", cartId, "cartProducts", this.productName);
                        const productDoc = await getDoc(productRef);
    
                        if (productDoc.exists) {
                            await updateDoc(productRef, {
                                quantity: productDoc.data().quantity + 1
                            });
                            
                        } else {
                            await setDoc(productRef, product);
                        }
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2

Answers


  1. Chosen as BEST ANSWER
    0

    solved using runTransaction

    import { runTransaction } from "firebase/firestore";
const productRef = doc(db, "carts", cartId, "cartProducts", this.productName);

                    try {
                        await runTransaction(db, async (transaction) => {
                            const newQ = await transaction.get(productRef);
                            if (!newQ.exists()) {
                                await setDoc(productRef, product);
                                throw " Document no exist ";
                            }
                            const newQuant = newQ.data().quantity + 1;
                            transaction.update(productRef, { quantity: newQuant });

                        });
                        console.log("Transaction successfully committed!");
                    } catch (e) {
                        console.log("Transaction failed: ", e);
                    }

  2. 0

    The error

    Error adding product to cart: TypeError: Cannot read properties of
    undefined (reading ‘quantity’)

    indicates that the field quantity is undefined in the productDoc.

    So either you enforce through security rules that quantity has a correct value when the productDoc doc is created/updated or you adapt your code to handle this case as follows, for example:

    const productRef = doc(db, "carts", cartId, "cartProducts", this.productName);
const productDoc = await getDoc(productRef);
console.log(JSON.stringify(productDoc.data()));
if (productDoc.exists && productDoc.data().quantity) {
    await updateDoc(productRef, {
        quantity: productDoc.data().quantity + 1
    });

} else {
    await setDoc(productRef, product);
}
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