Firebase 基于过滤器的 Firestore 查询

Question

Let's say I have a collection of 2000 documents with fields id, age, location in cloud firestore.

On client side(nodejs), I have 50 ids and want to perform a query on the firestore only for these 50 ids and should satisfy the conditions like age>25, location=chicago. I don't want to read all 50 documents. Want to read the documents from these 50 ids which satisfies the conditions I mentioned (The resulting documents could be less than 50) trying to reduce read operations. Is it possible to do this? Looking at the documentation I see there is in operator but my understanding is it only supports for 10 comparison values. Is it possible to query as per my requirement?

While creating the documents, I can adjust the documentId to be the field id if that makes the query possible.

Answer 1

Based on your requirement, you can still use comparison values like code below:

Firebase Web Version 8:

db.collection("users")
    .where("age", ">", "25")
    .where("location", "==", "chicago")
    .get()
    .then((querySnapshot) => {
        querySnapshot.forEach((doc) => {
            // doc.data() is never undefined for query doc snapshots
            console.log(doc.id, " => ", doc.data());
        });
    })
    .catch((error) => {
        console.log("Error getting documents: ", error);
    });

Firebase Web Version 9:

const q = query(collection(db, "users"), where("age", ">", "25"), where("location", "==", "chicago");

const querySnapshot = await getDocs(q);
querySnapshot.forEach((doc) => {
  // doc.data() is never undefined for query doc snapshots
  console.log(doc.id, " => ", doc.data());
});

You can use comparison value as much as you want using these operators ( < , <= , > , >= ). By using multiple where queries, it provides you a query statement with logical AND query. The only limitation are for logical OR queries which on these documentation states:

Cloud Firestore provides limited support for logical OR queries. The in, and array-contains-any operators support a logical OR of up to 10 equality (==) or array-contains conditions on a single field. For other cases, create a separate query for each OR condition and merge the query results in your app.

---

UPDATE:

If you want to query 50 documents at the same time. You can query it using FieldPath.documentID() and "IN" query. See code below:

const docArray = [
// Array of Document IDs.
];

db.collection("users")
    .where(firebase.firestore.FieldPath.documentId(), 'in', docArray)
    .where("age", ">", "25")
    .where("location", "==", "chicago")
    .get()
    .then((querySnapshot) => {
        querySnapshot.forEach((doc) => {
            // doc.data() is never undefined for query doc snapshots
            console.log(doc.id, " => ", doc.data());
        });
    })
    .catch((error) => {
        console.log("Error getting documents: ", error);
    });

As I stated on my previous answer, this only works if the array is of less than 10 items ( Firestore limitation ). If you need more, you'll have to either batch the IDs, into smaller arrays and perform multiple queries. Check code I written below:

// Consists of 11 values
const docArray = [
    '5fKmta1jgEiCQBZvSJ3Y',
    'BubAGhg6IZbnzU70wdPf',
    'FVEq9trqF2Hy8ROsAjeW',
    'Nhz0pF2z3zw3aBcmnpqs',
    'TYYDYyIiyhVuWp91h7OS',
    'VDDiUGKkGnwrdo8jmDpb',
    'VXnXEuNfrhUAM8UbZ2AH',
    'XukTkr4XBey3yqAvFa3d',
    'cSNI1NgHP8OEsDY66RBw',
    'eCPc9F1bpS1qXD9WGKE2',
    'eHdKQPhE7snnRjoWJzBK'
];
const chunkedArray = [];
const resArray = [];
var promises = [];

// Firestore query limit
size = 10;

for(var i = 0; i < docArray.length; i += size) {
chunkedArray.push(docArray.slice(i, i+size));
}

chunkedArray.forEach((chunked) => {
    promises.push(
        db.collection("users")
            .where(firebase.firestore.FieldPath.documentId(), 'in', chunked)
            .where("age", ">", "25")
            .where("location", "==", "chicago")
            .get()
            .then((querySnapshot) => {
                querySnapshot.forEach((doc) => {
                    resArray.push(doc.data());
                });
            })
            .catch((error) => {
                console.log("Error getting documents: ", error);
            })
    );
})

Promise.all(promises).then(() => 
    // Returns merged data from forEach
    console.log(resArray)
);

You can also simply iterate the IDs, and get() each document individually. Look example code below:

docArray.forEach((docId) => {
    promises.push(
        db.collection("users")
            .where(firebase.firestore.FieldPath.documentId(), '==', docId)
            // .where("age", ">", "25")
            // .where("location", "==", "chicago")
            .get()
            .then((querySnapshot) => {
                querySnapshot.forEach((doc) => {
                    resArray.push(doc.data());
                });
            })
            .catch((error) => {
                console.log("Error getting documents: ", error);
            })
    );
})

Promise.all(promises).then(() => 
    // Returns merged data from forEach
    console.log(resArray)
);