Can someone help clarify the distinction between get() and valueChanges() when executing a query in Angular Firestore?
Are there specific advantages or disadvantages to consider, such as differences in reads or costs?
Can someone help clarify the distinction between get() and valueChanges() when executing a query in Angular Firestore?
Are there specific advantages or disadvantages to consider, such as differences in reads or costs?
One key distinction between valueChanges and get() lies in the fact that when using get(), you retrieve the data only once. On the other hand, valueChanges (as well as snapshotChanges) is triggered automatically whenever there is a change in the database associated with the document or collection being observed.
This automatic process is one of the advantages of Firebase Realtime Database. It eliminates the need for manual polling or any additional steps to obtain the most up-to-date information; Firebase handles it all seamlessly!
In my view, get() can be particularly useful in scenarios where you update a document within a collection and immediately require access to that updated document just once. For instance:
const docRef= this.afs.collection(colId).doc(docId).set(...)
docRef.get().pipe(
map(doc => doc.data())
)
.subscribe(data => {
// Perform actions with the document
})
While it's possible to achieve similar results by using valueChanges along with pipe(take(1)) to limit the number of emissions, get() offers a simple solution in such cases.
valueChanges() is a feature found in the angularfire2 library. As stated in the documentation:
This function returns an Observable containing only the document data, without any Snapshot metadata.
For Angular projects, you can utilize the angularfire2 library which includes the convenient valueChanges() method.
The get() method is also commonly used to fetch the contents of a single document.
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