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189
ViewsHow can I decrement a field value from firestore after submitting a form successfully?
I have these collection of items from firestore:
- availability : true
- stocks: 100
- item: item1
I kind of wanted to decrement the stocks after submitting the form: I have these where() to compare if what the user chose is the same item from the one saved in the firestore.
function incrementCounter(collref) {
collref = firestore
.collection("items")
.doc()
.where(selectedItem, "==", selectedItem);
collref.update({
stocks: firestore.FieldValue.increment(-1),
});
}
This is how I'll submit my form and I've set the incrementCounter() after saving it:
const handleSubmit = (e) => {
e.preventDefault();
try {
const userRef = firestore.collection("users").doc(id);
const ref = userRef.set(
{
....
},
},
{ merge: true }
);
console.log(" saved");
incrementCounter();
} catch (err) {
console.log(err);
}
};
There's no error in submitting the form. However, the incrementCounter() is not working and displays this error:
TypeError: _Firebase_utils__WEBPACK_IMPORTED_MODULE_5__.firestore.collection(...).doc(...).where is not a function
2 answers
Answer question0
There are few problems here
- There should be async-await for both functions
- Your fieldValue should start from
firebase.firestore.FieldValue not firestoreFieldValue - Also
whereclause is used for collection, not doc() so remove that as well. Also I don't think this will update the full collection but do check it and see. (The error you are getting is because of this)
I don't know how you are importing firebase in this application and I don't know how you have declared firestore but mostly firestore variable is declared like this
const firestore = firebase.firestore();
In here firestore is a function, not a property
But when you are using it in the FieldValue then it should be like
firebase.firestore.FieldValue.increment(-1),
Notice that firestore here is a property not a function
Your full code should be like this
async function incrementCounter(collref) {
collref = firestore
.collection("items")
.where(selectedItem, "==", selectedItem);
const newRef = await collref.get();
for(let i in newRef.docs){
const doc = newRef.docs[i];
await doc.update({
stocks: firebase.firestore.FieldValue.increment(-1),
});
// You can also batch this
}
}
const handleSubmit = async (e) => {
e.preventDefault();
try {
const userRef = firestore.collection("users").doc(id);
const ref = await userRef.set(
{
....
},
},
{ merge: true }
);
console.log(" saved");
await incrementCounter();
} catch (err) {
console.log(err);
}
};
0
The where() method exists on a CollectionReference and not a DocumentReference. You also need to get references to those documents first so first get all the matching documents and then update all of them using Promise.all() or Batch Writes:
function incrementCounter() {
// not param required ^^
const collref = firestore
.collection("items")
// .doc() <-- remove this
.where(selectedItem, "==", selectedItem);
// ^^^ ^^^
// doc field field value
// "item" {selectedItemName}
collRef.get().then(async (qSnap) => {
const updates = []
qSnap.docs.forEach((doc) => {
updates.push(doc.ref.update({ stocks: firebase.firestore.FieldValue.increment(-1) }))
})
await Promise.all(updates)
})
}
If you are updating less than 500 documents, consider using batch writes to make sure all updates either fail or pass:
collRef.get().then(async (qSnap) => {
const batch = firestore.batch()
qSnap.docs.forEach((doc) => {
batch.update(doc.ref, { stocks: firebase.firestore.FieldValue.increment(-1) })
})
await batch.commit()
})
You can read more about batch writes in the documentation