Ordina e limita i dati con Cloud Firestore

Cloud Firestore offre potenti funzionalità di query per specificare quali documenti desideri recuperare da una raccolta. Queste query possono essere utilizzate anche con get() o addSnapshotListener() , come descritto in Get Data .

Ordinare e limitare i dati

Per impostazione predefinita, una query recupera tutti i documenti che soddisfano la query in ordine crescente per ID documento. Puoi specificare l'ordinamento per i tuoi dati utilizzando orderBy() e puoi limitare il numero di documenti recuperati utilizzando limit() . Se specifichi un limit() , il valore deve essere maggiore o uguale a zero.

Ad esempio, puoi cercare le prime 3 città in ordine alfabetico con:

import { query, orderBy, limit } from "firebase/firestore";  

const q = query(citiesRef, orderBy("name"), limit(3));
order_and_limit.js

citiesRef.orderBy("name").limit(3);
test.firestore.js

citiesRef.order(by: "name").limit(to: 3)
ViewController.swift

[[citiesRef queryOrderedByField:@"name"] queryLimitedTo:3];
ViewController.m

citiesRef.orderBy("name").limit(3)
DocSnippets.kt

citiesRef.orderBy("name").limit(3);
DocSnippets.java

final citiesRef = db.collection("cities");
citiesRef.orderBy("name").limit(3);
firestore.dart

Query query = cities.orderBy("name").limit(3);
Query query = cities.orderBy("name").limitToLast(3);
QueryDataSnippets.java

cities_ref = db.collection("cities")
query = cities_ref.order_by("name").limit_to_last(2)
results = query.get()
snippets.py

cities_ref = db.collection("cities")
query = cities_ref.order_by("name").limit_to_last(2)
results = await query.get()
snippets.py

cities_ref.OrderBy("name").Limit(3);
snippets.cpp

const firstThreeRes = await citiesRef.orderBy('name').limit(3).get();
index.js

query := cities.OrderBy("name", firestore.Asc).Limit(3)
query := cities.OrderBy("name", firestore.Asc).LimitToLast(3)
query.go

$query = $citiesRef->orderBy('name')->limit(3);
query_order_limit.php

Query query = citiesRef.OrderBy("Name").Limit(3);

Query query = citiesRef.OrderBy("Name").Limit(3);
Program.cs

query = cities_ref.order("name").limit(3)
order_limit_data.rb

Puoi anche ordinare in ordine decrescente per ottenere le ultime 3 città:

import { query, orderBy, limit } from "firebase/firestore";  

const q = query(citiesRef, orderBy("name", "desc"), limit(3));
order_and_limit_desc.js

citiesRef.orderBy("name", "desc").limit(3);
test.firestore.js

citiesRef.order(by: "name", descending: true).limit(to: 3)
ViewController.swift

[[citiesRef queryOrderedByField:@"name" descending:YES] queryLimitedTo:3];
ViewController.m

citiesRef.orderBy("name", Query.Direction.DESCENDING).limit(3)
DocSnippets.kt

citiesRef.orderBy("name", Direction.DESCENDING).limit(3);
DocSnippets.java

final citiesRef = db.collection("cities");
citiesRef.orderBy("name", descending: true).limit(3);
firestore.dart

Query query = cities.orderBy("name", Direction.DESCENDING).limit(3);
QueryDataSnippets.java

cities_ref = db.collection('cities')
query = cities_ref.order_by(
    'name', direction=firestore.Query.DESCENDING).limit(3)
results = query.stream()
snippets.py

cities_ref = db.collection("cities")
query = cities_ref.order_by("name", direction=firestore.Query.DESCENDING).limit(3)
results = query.stream()
snippets.py

cities_ref.OrderBy("name", Query::Direction::kDescending).Limit(3);
snippets.cpp

const lastThreeRes = await citiesRef.orderBy('name', 'desc').limit(3).get();
index.js

query := cities.OrderBy("name", firestore.Desc).Limit(3)
query.go

$query = $citiesRef->orderBy('name', 'DESC')->limit(3);
query_order_desc_limit.php

Query query = citiesRef.OrderByDescending("Name").Limit(3);

Query query = citiesRef.OrderByDescending("Name").Limit(3);
Program.cs

query = cities_ref.order("name", "desc").limit(3)
order_limit_data.rb

Puoi anche ordinare per più campi. Ad esempio, se si desidera ordinare per stato e all'interno di ogni stato ordinare per popolazione in ordine decrescente:

import { query, orderBy } from "firebase/firestore";  

const q = query(citiesRef, orderBy("state"), orderBy("population", "desc"));
order_multiple.js

citiesRef.orderBy("state").orderBy("population", "desc");
test.firestore.js

citiesRef
    .order(by: "state")
    .order(by: "population", descending: true)
ViewController.swift

[[citiesRef queryOrderedByField:@"state"] queryOrderedByField:@"population" descending:YES];
ViewController.m

citiesRef.orderBy("state").orderBy("population", Query.Direction.DESCENDING)
DocSnippets.kt

citiesRef.orderBy("state").orderBy("population", Direction.DESCENDING);
DocSnippets.java

final citiesRef = db.collection("cities");
citiesRef.orderBy("state").orderBy("population", descending: true);
firestore.dart

Query query = cities.orderBy("state").orderBy("population", Direction.DESCENDING);
QueryDataSnippets.java

cities_ref = db.collection('cities')
cities_ref.order_by('state').order_by(
    'population', direction=firestore.Query.DESCENDING)
snippets.py

cities_ref = db.collection("cities")
cities_ref.order_by("state").order_by(
    "population", direction=firestore.Query.DESCENDING
)
snippets.py

cities_ref.OrderBy("state").OrderBy("name", Query::Direction::kDescending);
snippets.cpp

const byStateByPopRes = await citiesRef.orderBy('state').orderBy('population', 'desc').get();
index.js

query := client.Collection("cities").OrderBy("state", firestore.Asc).OrderBy("population", firestore.Desc)
query.go

$query = $citiesRef->orderBy('state')->orderBy('population', 'DESC');
query_order_multi.php

Query query = citiesRef.OrderBy("State").OrderByDescending("Population");

Query query = citiesRef.OrderBy("State").OrderByDescending("Population");
Program.cs

query = cities_ref.order("state").order("population", "desc")
order_limit_data.rb

Puoi combinare i filtri where() con orderBy() e limit() . Nell'esempio seguente, le query definiscono una soglia di popolazione, ordinano per popolazione in ordine crescente e restituiscono solo i primi risultati che superano la soglia:

import { query, where, orderBy, limit } from "firebase/firestore";  

const q = query(citiesRef, where("population", ">", 100000), orderBy("population"), limit(2));
filter_and_order.js

citiesRef.where("population", ">", 100000).orderBy("population").limit(2);
test.firestore.js

citiesRef
    .whereField("population", isGreaterThan: 100000)
    .order(by: "population")
    .limit(to: 2)
ViewController.swift

[[[citiesRef queryWhereField:@"population" isGreaterThan:@100000]
    queryOrderedByField:@"population"]
    queryLimitedTo:2];
ViewController.m

citiesRef.whereGreaterThan("population", 100000).orderBy("population").limit(2)
DocSnippets.kt

citiesRef.whereGreaterThan("population", 100000).orderBy("population").limit(2);
DocSnippets.java

final citiesRef = db.collection("cities");
citiesRef
    .where("population", isGreaterThan: 100000)
    .orderBy("population")
    .limit(2);
firestore.dart

Query query = cities.whereGreaterThan("population", 2500000L).orderBy("population").limit(2);
QueryDataSnippets.java

cities_ref = db.collection('cities')
query = cities_ref.where(
    'population', '>', 2500000).order_by('population').limit(2)
results = query.stream()
snippets.py

cities_ref = db.collection("cities")
query = cities_ref.where("population", ">", 2500000).order_by("population").limit(2)
results = query.stream()
snippets.py

cities_ref.WhereGreaterThan("population", FieldValue::Integer(100000))
    .OrderBy("population")
    .Limit(2);
snippets.cpp

const biggestRes = await citiesRef.where('population', '>', 2500000)
  .orderBy('population').limit(2).get();
index.js

query := cities.Where("population", ">", 2500000).OrderBy("population", firestore.Desc).Limit(2)
query.go

$query = $citiesRef
    ->where('population', '>', 2500000)
    ->orderBy('population')
    ->limit(2);
query_order_limit_field_valid.php

Query query = citiesRef
    .WhereGreaterThan("Population", 2500000)
    .OrderBy("Population")
    .Limit(2);

Query query = citiesRef
    .WhereGreaterThan("Population", 2500000)
    .OrderBy("Population")
    .Limit(2);
Program.cs

query = cities_ref.where("population", ">", 2_500_000).order("population").limit(2)
order_limit_data.rb

Tuttavia, se disponi di un filtro con un confronto tra intervalli ( < , <= , > , >= ), il tuo primo ordinamento deve essere sullo stesso campo, consulta l'elenco delle limitazioni orderBy() di seguito.

Limitazioni

Tieni presente le seguenti restrizioni per le clausole orderBy() :

• Una clausola orderBy() filtra anche l'esistenza dei campi specificati . Il set di risultati non includerà i documenti che non contengono i campi specificati.

• Se includi un filtro con un confronto tra intervalli ( < , <= , > , >= ), il tuo primo ordinamento deve essere sullo stesso campo:

  Valido : Filtro intervallo e orderBy sullo stesso campo

  Web modular API

  import { query, where, orderBy } from "firebase/firestore";  
  
  const q = query(citiesRef, where("population", ">", 100000), orderBy("population"));
  valid_filter_and_order.js

  Web namespaced API

  citiesRef.where("population", ">", 100000).orderBy("population");
  test.firestore.js

  Rapido

  Nota: questo prodotto non è disponibile sui target watchOS e App Clip.

  citiesRef
      .whereField("population", isGreaterThan: 100000)
      .order(by: "population")
  ViewController.swift

  Obiettivo-C

  Nota: questo prodotto non è disponibile sui target watchOS e App Clip.

  [[citiesRef queryWhereField:@"population" isGreaterThan:@100000]
      queryOrderedByField:@"population"];
  ViewController.m

  Kotlin+KTX

  citiesRef.whereGreaterThan("population", 100000).orderBy("population")
  DocSnippets.kt

  Java

  citiesRef.whereGreaterThan("population", 100000).orderBy("population");
  DocSnippets.java

  Dart

  final citiesRef = db.collection("cities");
  citiesRef.where("population", isGreaterThan: 100000).orderBy("population");
  firestore.dart

  Giava

  Query query = cities.whereGreaterThan("population", 2500000L).orderBy("population");
  QueryDataSnippets.java

  Pitone

  cities_ref = db.collection('cities')
  query = cities_ref.where(
      'population', '>', 2500000).order_by('population')
  results = query.stream()
  snippets.py

  Python

  cities_ref = db.collection("cities")
  query = cities_ref.where("population", ">", 2500000).order_by("population")
  results = query.stream()
  snippets.py

  Node.js

  citiesRef.where('population', '>', 2500000).orderBy('population');
  index.js

  Andare

  query := cities.Where("population", ">", 2500000).OrderBy("population", firestore.Asc)
  query.go

  PHP

  PHP

  Per ulteriori informazioni sull'installazione e la creazione di un client Cloud Firestore, fai riferimento a Librerie client Cloud Firestore .

  $query = $citiesRef
      ->where('population', '>', 2500000)
      ->orderBy('population');
  query_order_with_filter.php

  Unità

  Query query = citiesRef
      .WhereGreaterThan("Population", 2500000)
      .OrderBy("Population");

  C#

  Query query = citiesRef
      .WhereGreaterThan("Population", 2500000)
      .OrderBy("Population");
  Program.cs

  Rubino

  query = cities_ref.where("population", ">", 2_500_000).order("population")
  order_limit_data.rb

  Non valido : filtro intervallo e primo orderBy su campi diversi

  Web modular API

  import { query, where, orderBy } from "firebase/firestore";  
  
  const q = query(citiesRef, where("population", ">", 100000), orderBy("country"));
  invalid_filter_and_order.js

  Web namespaced API

  citiesRef.where("population", ">", 100000).orderBy("country");
  test.firestore.js

  Rapido

  Nota: questo prodotto non è disponibile sui target watchOS e App Clip.

  citiesRef
      .whereField("population", isGreaterThan: 100000)
      .order(by: "country")
  ViewController.swift

  Obiettivo-C

  Nota: questo prodotto non è disponibile sui target watchOS e App Clip.

  [[citiesRef queryWhereField:@"population" isGreaterThan:@100000] queryOrderedByField:@"country"];
  ViewController.m

  Kotlin+KTX

  citiesRef.whereGreaterThan("population", 100000).orderBy("country")
  DocSnippets.kt

  Java

  citiesRef.whereGreaterThan("population", 100000).orderBy("country");
  DocSnippets.java

  Dart

  final citiesRef = db.collection("cities");
  citiesRef.where("population", isGreaterThan: 100000).orderBy("country");
  firestore.dart

  Giava

  Query query = cities.whereGreaterThan("population", 2500000L).orderBy("country");
  QueryDataSnippets.java

  Pitone

  cities_ref = db.collection('cities')
  query = cities_ref.where('population', '>', 2500000).order_by('country')
  results = query.stream()
  snippets.py

  Python

  cities_ref = db.collection("cities")
  query = cities_ref.where("population", ">", 2500000).order_by("country")
  results = query.stream()
  snippets.py

  C++

  // BAD EXAMPLE -- will crash the program:
  cities_ref.WhereGreaterThan("population", FieldValue::Integer(100000))
      .OrderBy("country");
  snippets.cpp

  Node.js

  citiesRef.where('population', '>', 2500000).orderBy('country');
  index.js

  Andare

  // Note: This is an invalid query. It violates the constraint that range
  // and order by are required to be on the same field.
  query := cities.Where("population", ">", 2500000).OrderBy("country", firestore.Asc)
  query.go

  PHP

  PHP

  Per ulteriori informazioni sull'installazione e la creazione di un client Cloud Firestore, fai riferimento a Librerie client Cloud Firestore .

  $invalidRangeQuery = $citiesRef
      ->where('population', '>', 2500000)
      ->orderBy('country');
  query_order_field_invalid.php

  Unità

  Query query = citiesRef
      .WhereGreaterThan("Population", 2500000)
      .OrderBy("Country");

  C#

  Query query = citiesRef
      .WhereGreaterThan("Population", 2500000)
      .OrderBy("Country");
  Program.cs

  Rubino

  query = cities_ref.where("population", ">", 2_500_000).order("country")
  order_limit_data.rb

• Non è possibile ordinare la query in base a qualsiasi campo incluso in un'uguaglianza ( = ) o in una clausola.

orderBy ed esistenza

Quando si ordina una query in base a un determinato campo, la query può restituire solo i documenti in cui esiste il campo order-by.

Ad esempio, la query seguente non restituirà alcun documento in cui il campo population non è impostato, anche se soddisfano i filtri di query.

db.collection("cities").whereEqualTo("country", “USA”).orderBy(“population”);

Un effetto correlato si applica alle disuguaglianze. Una query con un filtro di disuguaglianza su un campo implica anche l'ordinamento in base a tale campo. La query seguente non restituisce documenti senza un campo population anche se country = USA in quel documento. Per ovviare al problema, puoi eseguire query separate per ogni ordinamento oppure puoi assegnare un valore a tutti i campi in base a cui ordini.

db.collection(“cities”).where(or(“country”, USA”), greaterThan(“population”, 250000));

La query precedente include un ordine implicito sulla disuguaglianza ed è equivalente alla seguente:

db.collection(“cities”).where(or(“country”, USA”), greaterThan(“population”, 250000)).orderBy(“population”);