Get data by id from firebase - node.js

Question

I use firebase on node.js .
My given structure should look like this:
{
...
batch-1:
id-1(suppose):
name:...
phone:...
id-2:
...
id-3:
...
batch-2:
...
batch-3:
...
...
batch-n:
...
}
How can I get an id-1 object by its identifier in such an architecture?
Does the database have to go around all the batches?
Is there a better solution?
The main task: Create a batch with many objects that will have SHORT and a UNIQUE identifier and optimally receive data by this identifier

Answer 1

To search for a particular ID that is a child of a list of unknown IDs, you need to use orderByChild(). In your use case, you are looking for a particular ID in a list of batch IDs. If you used orderByChild() on this list, you would get back results for each and every batch ID, even if it didn't have the ID you wanted. This is because even null (non-existant) values are included (and sorted at the start) in the results. To get the data of the desired ID, you would get the data for the last result of the query, which if it existed, would be sorted to the end of the list. Note that if the desired ID doesn't exist, the last result (if there are any results) would have a null value. To return only the last result of the query, you would use limitToLast(1).
Putting this all together, gives the following code:
let idToFind = "unique-id-1";
let batchesRef = firebase.database().ref(); // parent key of "batch-1", "batch-2", etc.
// assumed to be the database root here
batchesRef.orderByChild(idToFind).limitToLast(1).once('value')
.then((querySnapshot) => {
if (!querySnapshot.numChildren()) { // handle rare no-results case
throw new Error('expected at least one result');
}
let dataSnapshot;
querySnapshot.forEach((snap) => dataSnapshot = snap); // get the snapshot we want out of the query's results list
if (!dataSnapshot.exists()) { // value may be null, meaning idToFind doesn't exist
throw new Error(`Entry ${idToFind} not found.`);
}
// do what you want with dataSnapshot
console.log(`Entry ${idToFind}'s data is:`, dataSnapshot.val());
})
.catch((error) => {
console.log("Unexpected error:", error);
})
For small data sets, the above code will work just fine. But if the list of batches starts growing quite large, you may wish to build an index that maps a particular ID to the batch ID that contains it.

Answer 2

Here is my method which allows you to search by id or to search by key value such as email uniqueemail
// gets primary key
const getSnapshotValKey = snapshot => (Object.keys(snapshot).length > 0 ? Object.keys(snapshot)[0] : null)
const getUser = async ({ id, key, value }) => {
let user = null
const ref = id ? '/users/' + id : 'users'
const userRef = admin.database().ref(ref)
const valueRef = id ? userRef : await userRef.orderByChild(key).equalTo(value)
const snapshot = await valueRef.once('value')
const val = snapshot.val()
if (val) {
const key = id || getSnapshotValKey(val)
user = {
id: key,
...(id ? val : val[key]),
}
}
return user
}