Impaginazione dei dati con cursori di query
Con i cursori di query in Firestore, puoi suddividere i dati restituiti da una query in batch in base ai parametri definiti nella query.
I cursori di query definiscono i punti di inizio e di fine di una query, consentendoti di:
- Restituisce un sottoinsieme di dati.
- Impagina i risultati della query.
Tuttavia, per definire un intervallo specifico per una query, devi utilizzare il metodo where()
descritto in Query semplici.
Aggiungere un cursore semplice a una query
Utilizza i metodi startAt()
o startAfter()
per definire il punto di partenza per una query.
Il metodo startAt()
include il punto iniziale, mentre il metodo startAfter()
lo esclude.
Ad esempio, se utilizzi startAt(A)
in una query, viene restituito l'intero alfabeto.
Se utilizzi invece startAfter(A)
, restituisce B-Z
.
Versione web 9
import { query, orderBy, startAt } from "firebase/firestore"; const q = query(citiesRef, orderBy("population"), startAt(1000000));
Versione web 8
citiesRef.orderBy("population").startAt(1000000);
Swift
// Get all cities with population over one million, ordered by population. db.collection("cities") .order(by: "population") .start(at: [1000000])
Objective-C
// Get all cities with population over one million, ordered by population. [[[db collectionWithPath:@"cities"] queryOrderedByField:@"population"] queryStartingAtValues:@[ @1000000 ]];
Java
Android
// Get all cities with a population >= 1,000,000, ordered by population, db.collection("cities") .orderBy("population") .startAt(1000000);
Kotlin+KTX
Android
// Get all cities with a population >= 1,000,000, ordered by population, db.collection("cities") .orderBy("population") .startAt(1000000)
Freccetto
db.collection("cities").orderBy("population").startAt([1000000]);
Java
Python
Python
(asincrono)
C++
// Get all cities with a population >= 1,000,000, ordered by population, db->Collection("cities") .OrderBy("population") .StartAt({FieldValue::Integer(1000000)});
Node.js
Go
PHP
$query = $citiesRef ->orderBy('population') ->startAt([1000000]);
Unity
Query query = citiesRef.OrderBy("Population").StartAt(1000000);
C#
Query query = citiesRef.OrderBy("Population").StartAt(1000000);
Ruby
Analogamente, utilizza i metodi endAt()
o endBefore()
per definire un punto di arrivo per i risultati della query.
Versione web 9
import { query, orderBy, endAt } from "firebase/firestore"; const q = query(citiesRef, orderBy("population"), endAt(1000000));
Versione web 8
citiesRef.orderBy("population").endAt(1000000);
Swift
// Get all cities with population less than one million, ordered by population. db.collection("cities") .order(by: "population") .end(at: [1000000])
Objective-C
// Get all cities with population less than one million, ordered by population. [[[db collectionWithPath:@"cities"] queryOrderedByField:@"population"] queryEndingAtValues:@[ @1000000 ]];
Java
Android
// Get all cities with a population <= 1,000,000, ordered by population, db.collection("cities") .orderBy("population") .endAt(1000000);
Kotlin+KTX
Android
// Get all cities with a population <= 1,000,000, ordered by population, db.collection("cities") .orderBy("population") .endAt(1000000)
Freccetto
db.collection("cities").orderBy("population").endAt([1000000]);
Java
Python
Python
(asincrono)
C++
// Get all cities with a population <= 1,000,000, ordered by population, db->Collection("cities") .OrderBy("population") .EndAt({FieldValue::Integer(1000000)});
Node.js
Go
PHP
$query = $citiesRef ->orderBy('population') ->endAt([1000000]);
Unity
Query query = citiesRef.OrderBy("Population").EndAt(1000000);
C#
Query query = citiesRef.OrderBy("Population").EndAt(1000000);
Ruby
Utilizza uno snapshot di documento per definire il cursore delle query
Puoi anche passare uno snapshot di documento alla clausola del cursore come punto di inizio o di fine del cursore di query. I valori nello snapshot del documento fungono da valori nel cursore della query.
Ad esempio, scatta un'istantanea di un documento "San Francisco" nel tuo set di dati di città e popolazioni. Quindi, utilizza l'istantanea del documento come punto di partenza per il cursore della query di compilazione. La query restituirà tutte le città con una popolazione maggiore o uguale a San Francisco, come definito nell'istantanea del documento.
Versione web 9
import { collection, doc, getDoc, query, orderBy, startAt } from "firebase/firestore"; const citiesRef = collection(db, "cities"); const docSnap = await getDoc(doc(citiesRef, "SF")); // Get all cities with a population bigger than San Francisco const biggerThanSf = query(citiesRef, orderBy("population"), startAt(docSnap)); // ...
Versione web 8
var citiesRef = db.collection("cities"); return citiesRef.doc("SF").get().then((doc) => { // Get all cities with a population bigger than San Francisco var biggerThanSf = citiesRef .orderBy("population") .startAt(doc); // ... });
Swift
db.collection("cities") .document("SF") .addSnapshotListener { (document, error) in guard let document = document else { print("Error retreving cities: \(error.debugDescription)") return } // Get all cities with a population greater than or equal to San Francisco. let sfSizeOrBigger = db.collection("cities") .order(by: "population") .start(atDocument: document) }
Objective-C
[[[db collectionWithPath:@"cities"] documentWithPath:@"SF"] addSnapshotListener:^(FIRDocumentSnapshot *snapshot, NSError *error) { if (snapshot == nil) { NSLog(@"Error retreiving cities: %@", error); return; } // Get all cities with a population greater than or equal to San Francisco. FIRQuery *sfSizeOrBigger = [[[db collectionWithPath:@"cities"] queryOrderedByField:@"population"] queryStartingAtDocument:snapshot]; }];
Java
Android
// Get the data for "San Francisco" db.collection("cities").document("SF") .get() .addOnSuccessListener(new OnSuccessListener<DocumentSnapshot>() { @Override public void onSuccess(DocumentSnapshot documentSnapshot) { // Get all cities with a population bigger than San Francisco. Query biggerThanSf = db.collection("cities") .orderBy("population") .startAt(documentSnapshot); // ... } });
Kotlin+KTX
Android
// Get the data for "San Francisco" db.collection("cities").document("SF") .get() .addOnSuccessListener { documentSnapshot -> // Get all cities with a population bigger than San Francisco. val biggerThanSf = db.collection("cities") .orderBy("population") .startAt(documentSnapshot) // ... }
Freccetto
db.collection("cities").doc("SF").get().then( (documentSnapshot) { final biggerThanSf = db .collection("cities") .orderBy("population") .startAt([documentSnapshot]); }, onError: (e) => print("Error: $e"), );
Java
Python
Python
(asincrono)
C++
db->Collection("cities").Document("SF").Get().OnCompletion( [db](const Future<DocumentSnapshot>& future) { if (future.error() == Error::kErrorOk) { const DocumentSnapshot& document_snapshot = *future.result(); Query bigger_than_sf = db->Collection("cities") .OrderBy("population") .StartAt({document_snapshot}); // ... } });
Node.js
Go
PHP
$citiesRef = $db->collection('samples/php/cities'); $docRef = $citiesRef->document('SF'); $snapshot = $docRef->snapshot(); $query = $citiesRef ->orderBy('population') ->startAt($snapshot);
Unity
CollectionReference citiesRef = db.Collection("cities"); DocumentReference docRef = citiesRef.Document("SF"); docRef.GetSnapshotAsync().ContinueWith((snapshotTask) => { Query query = citiesRef.OrderBy("Population").StartAt(snapshotTask.Result); });
C#
CollectionReference citiesRef = db.Collection("cities"); DocumentReference docRef = citiesRef.Document("SF"); DocumentSnapshot snapshot = await docRef.GetSnapshotAsync(); Query query = citiesRef.OrderBy("Population").StartAt(snapshot);
Ruby
Impaginare una query
Impagina le query combinando i cursori delle query con il metodo limit()
.
Ad esempio, utilizza l'ultimo documento di un gruppo come inizio di un cursore per il batch successivo.
Versione web 9
import { collection, query, orderBy, startAfter, limit, getDocs } from "firebase/firestore"; // Query the first page of docs const first = query(collection(db, "cities"), orderBy("population"), limit(25)); const documentSnapshots = await getDocs(first); // Get the last visible document const lastVisible = documentSnapshots.docs[documentSnapshots.docs.length-1]; console.log("last", lastVisible); // Construct a new query starting at this document, // get the next 25 cities. const next = query(collection(db, "cities"), orderBy("population"), startAfter(lastVisible), limit(25));
Versione web 8
var first = db.collection("cities") .orderBy("population") .limit(25); return first.get().then((documentSnapshots) => { // Get the last visible document var lastVisible = documentSnapshots.docs[documentSnapshots.docs.length-1]; console.log("last", lastVisible); // Construct a new query starting at this document, // get the next 25 cities. var next = db.collection("cities") .orderBy("population") .startAfter(lastVisible) .limit(25); });
Swift
// Construct query for first 25 cities, ordered by population let first = db.collection("cities") .order(by: "population") .limit(to: 25) first.addSnapshotListener { (snapshot, error) in guard let snapshot = snapshot else { print("Error retreving cities: \(error.debugDescription)") return } guard let lastSnapshot = snapshot.documents.last else { // The collection is empty. return } // Construct a new query starting after this document, // retrieving the next 25 cities. let next = db.collection("cities") .order(by: "population") .start(afterDocument: lastSnapshot) // Use the query for pagination. // ... }
Objective-C
FIRQuery *first = [[[db collectionWithPath:@"cities"] queryOrderedByField:@"population"] queryLimitedTo:25]; [first addSnapshotListener:^(FIRQuerySnapshot *snapshot, NSError *error) { if (snapshot == nil) { NSLog(@"Error retreiving cities: %@", error); return; } if (snapshot.documents.count == 0) { return; } FIRDocumentSnapshot *lastSnapshot = snapshot.documents.lastObject; // Construct a new query starting after this document, // retreiving the next 25 cities. FIRQuery *next = [[[db collectionWithPath:@"cities"] queryOrderedByField:@"population"] queryStartingAfterDocument:lastSnapshot]; // Use the query for pagination. // ... }];
Java
Android
// Construct query for first 25 cities, ordered by population Query first = db.collection("cities") .orderBy("population") .limit(25); first.get() .addOnSuccessListener(new OnSuccessListener<QuerySnapshot>() { @Override public void onSuccess(QuerySnapshot documentSnapshots) { // ... // Get the last visible document DocumentSnapshot lastVisible = documentSnapshots.getDocuments() .get(documentSnapshots.size() -1); // Construct a new query starting at this document, // get the next 25 cities. Query next = db.collection("cities") .orderBy("population") .startAfter(lastVisible) .limit(25); // Use the query for pagination // ... } });
Kotlin+KTX
Android
// Construct query for first 25 cities, ordered by population val first = db.collection("cities") .orderBy("population") .limit(25) first.get() .addOnSuccessListener { documentSnapshots -> // ... // Get the last visible document val lastVisible = documentSnapshots.documents[documentSnapshots.size() - 1] // Construct a new query starting at this document, // get the next 25 cities. val next = db.collection("cities") .orderBy("population") .startAfter(lastVisible) .limit(25) // Use the query for pagination // ... }
Freccetto
// Construct query for first 25 cities, ordered by population final first = db.collection("cities").orderBy("population").limit(25); first.get().then( (documentSnapshots) { // Get the last visible document final lastVisible = documentSnapshots.docs[documentSnapshots.size - 1]; // Construct a new query starting at this document, // get the next 25 cities. final next = db .collection("cities") .orderBy("population") .startAfter([lastVisible]).limit(25); // Use the query for pagination // ... }, onError: (e) => print("Error completing: $e"), );
Java
Python
Python
(asincrono)
C++
// Construct query for first 25 cities, ordered by population Query first = db->Collection("cities").OrderBy("population").Limit(25); first.Get().OnCompletion([db](const Future<QuerySnapshot>& future) { if (future.error() != Error::kErrorOk) { // Handle error... return; } // Get the last visible document const QuerySnapshot& document_snapshots = *future.result(); std::vector<DocumentSnapshot> documents = document_snapshots.documents(); const DocumentSnapshot& last_visible = documents.back(); // Construct a new query starting at this document, // get the next 25 cities. Query next = db->Collection("cities") .OrderBy("population") .StartAfter(last_visible) .Limit(25); // Use the query for pagination // ... });
Node.js
Go
PHP
$citiesRef = $db->collection('samples/php/cities'); $firstQuery = $citiesRef->orderBy('population')->limit(3); # Get the last document from the results $documents = $firstQuery->documents(); $lastPopulation = 0; foreach ($documents as $document) { $lastPopulation = $document['population']; } # Construct a new query starting at this document # Note: this will not have the desired effect if multiple cities have the exact same population value $nextQuery = $citiesRef->orderBy('population')->startAfter([$lastPopulation]); $snapshot = $nextQuery->documents();
Unity
CollectionReference citiesRef = db.Collection("cities"); Query firstQuery = citiesRef.OrderBy("Population").Limit(3); // Get the last document from the results firstQuery.GetSnapshotAsync().ContinueWith((querySnapshotTask) => { long lastPopulation = 0; foreach (DocumentSnapshot documentSnapshot in querySnapshotTask.Result.Documents) { lastPopulation = documentSnapshot.GetValue<long>("Population"); } // Construct a new query starting at this document. // Note: this will not have the desired effect if multiple cities have the exact same population value Query secondQuery = citiesRef.OrderBy("Population").StartAfter(lastPopulation); Task<QuerySnapshot> secondQuerySnapshot = secondQuery.GetSnapshotAsync();
C#
CollectionReference citiesRef = db.Collection("cities"); Query firstQuery = citiesRef.OrderBy("Population").Limit(3); // Get the last document from the results QuerySnapshot querySnapshot = await firstQuery.GetSnapshotAsync(); long lastPopulation = 0; foreach (DocumentSnapshot documentSnapshot in querySnapshot.Documents) { lastPopulation = documentSnapshot.GetValue<long>("Population"); } // Construct a new query starting at this document. // Note: this will not have the desired effect if multiple cities have the exact same population value Query secondQuery = citiesRef.OrderBy("Population").StartAfter(lastPopulation); QuerySnapshot secondQuerySnapshot = await secondQuery.GetSnapshotAsync();
Ruby
Imposta il cursore in base a più campi
Quando utilizzi un cursore basato su un valore di campo (non un DocumentSnapshot), puoi rendere la posizione del cursore più precisa aggiungendo campi aggiuntivi. Ciò è particolarmente utile se il set di dati include più documenti che hanno tutti lo stesso valore per il campo del cursore, rendendo la posizione del cursore ambigua. Puoi aggiungere valori di campo aggiuntivi al cursore per specificare ulteriormente il punto di partenza o di arrivo e ridurre le ambiguità.
Ad esempio, in un set di dati contenente tutte le città denominate "Springfield". Negli Stati Uniti, ci saranno più punti di partenza per l'avvio di una query da "Springfield".
Città | |
---|---|
Nome | Stato |
Springfield | Massachusetts |
Springfield | Missouri |
Springfield | Wisconsin |
Per iniziare da uno Springfield specifico, puoi aggiungere lo stato come condizione secondaria nella clausola del cursore.
Versione web 9
// Will return all Springfields import { collection, query, orderBy, startAt } from "firebase/firestore"; const q1 = query(collection(db, "cities"), orderBy("name"), orderBy("state"), startAt("Springfield")); // Will return "Springfield, Missouri" and "Springfield, Wisconsin" const q2 = query(collection(db, "cities"), orderBy("name"), orderBy("state"), startAt("Springfield", "Missouri"));
Versione web 8
// Will return all Springfields db.collection("cities") .orderBy("name") .orderBy("state") .startAt("Springfield"); // Will return "Springfield, Missouri" and "Springfield, Wisconsin" db.collection("cities") .orderBy("name") .orderBy("state") .startAt("Springfield", "Missouri");
Swift
// Will return all Springfields db.collection("cities") .order(by: "name") .order(by: "state") .start(at: ["Springfield"]) // Will return "Springfield, Missouri" and "Springfield, Wisconsin" db.collection("cities") .order(by: "name") .order(by: "state") .start(at: ["Springfield", "Missouri"])
Objective-C
// Will return all Springfields [[[[db collectionWithPath:@"cities"] queryOrderedByField:@"name"] queryOrderedByField:@"state"] queryStartingAtValues:@[ @"Springfield" ]]; // Will return "Springfield, Missouri" and "Springfield, Wisconsin" [[[[db collectionWithPath:@"cities"] queryOrderedByField:@"name"] queryOrderedByField:@"state"] queryStartingAtValues:@[ @"Springfield", @"Missouri" ]];
Java
Android
// Will return all Springfields db.collection("cities") .orderBy("name") .orderBy("state") .startAt("Springfield"); // Will return "Springfield, Missouri" and "Springfield, Wisconsin" db.collection("cities") .orderBy("name") .orderBy("state") .startAt("Springfield", "Missouri");
Kotlin+KTX
Android
// Will return all Springfields db.collection("cities") .orderBy("name") .orderBy("state") .startAt("Springfield") // Will return "Springfield, Missouri" and "Springfield, Wisconsin" db.collection("cities") .orderBy("name") .orderBy("state") .startAt("Springfield", "Missouri")
Freccetto
// Will return all Springfields db .collection("cities") .orderBy("name") .orderBy("state") .startAt(["Springfield"]); // Will return "Springfield, Missouri" and "Springfield, Wisconsin" db .collection("cities") .orderBy("name") .orderBy("state") .startAt(["Springfield", "Missouri"]);
Java
Python
Python
(asincrono)
C++
// This is not yet supported.
Node.js
Go
PHP
// Will return all Springfields $query1 = $db ->collection('samples/php/cities') ->orderBy('name') ->orderBy('state') ->startAt(['Springfield']); // Will return "Springfield, Missouri" and "Springfield, Wisconsin" $query2 = $db ->collection('samples/php/cities') ->orderBy('name') ->orderBy('state') ->startAt(['Springfield', 'Missouri']);
Unity
Query query1 = db.Collection("cities").OrderBy("Name").OrderBy("State").StartAt("Springfield"); Query query2 = db.Collection("cities").OrderBy("Name").OrderBy("State").StartAt("Springfield", "Missouri");
C#
Query query1 = db.Collection("cities").OrderBy("Name").OrderBy("State").StartAt("Springfield"); Query query2 = db.Collection("cities").OrderBy("Name").OrderBy("State").StartAt("Springfield", "Missouri");