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Ordenar e limitar dados com o Cloud Firestore

Com o Cloud Firestore, você tem uma funcionalidade eficiente de consulta para especificar os documentos de uma coleção que queira recuperar. Também é possível usar essas consultas com get() ou addSnapshotListener(), conforme descrito em Receber dados.

Ordenar e limitar dados

Por padrão, uma consulta recupera todos os documentos que atendem a ela em ordem crescente por ID. É possível especificar a ordem de classificação dos dados usando orderBy() e limitar o número de documentos recuperados por meio de limit().

Por exemplo, para consultar as três primeiras cidades em ordem alfabética, use o seguinte:

Web
citiesRef.orderBy("name").limit(3)
Swift
citiesRef.order(by: "name").limit(to: 3)
Objective-C
[[citiesRef queryOrderedByField:@"name"] queryLimitedTo:3];
  
Java
Android
citiesRef.orderBy("name").limit(3);
Kotlin
Android
citiesRef.orderBy("name").limit(3)
Java
Query query = cities.orderBy("name").limit(3);
Python
db.collection(u'cities').order_by(u'name').limit(3).get()
Node.js
var firstThree = citiesRef.orderBy('name').limit(3);
Go
query := cities.OrderBy("name", firestore.Asc).Limit(3)
PHP
$query = $citiesRef->orderBy('name')->limit(3);
C#
Query query = citiesRef.OrderBy("Name").Limit(3);
Ruby
query = cities_ref.order("name").limit(3)

Para classificar em ordem decrescente as três últimas cidades, use o seguinte:

Web
citiesRef.orderBy("name", "desc").limit(3)
Swift
citiesRef.order(by: "name", descending: true).limit(to: 3)
Objective-C
[[citiesRef queryOrderedByField:@"name" descending:YES] queryLimitedTo:3];
  
Java
Android
citiesRef.orderBy("name", Direction.DESCENDING).limit(3);
Kotlin
Android
citiesRef.orderBy("name", Query.Direction.DESCENDING).limit(3)
Java
Query query = cities.orderBy("name", Direction.DESCENDING).limit(3);
Python
cities_ref = db.collection(u'cities')
query = cities_ref.order_by(
    u'name', direction=firestore.Query.DESCENDING).limit(3)
results = query.get()
Node.js
var lastThree = citiesRef.orderBy('name', 'desc').limit(3);
Go
query := cities.OrderBy("name", firestore.Desc).Limit(3)
PHP
$query = $citiesRef->orderBy('name', 'DESC')->limit(3);
C#
Query query = citiesRef.OrderByDescending("Name").Limit(3);
Ruby
query = cities_ref.order("name", "desc").limit(3)

Além disso, também é possível ordenar por vários campos. Por exemplo, isso pode ser feito por estado e, dentro de cada estado, por população em ordem decrescente:

Web
citiesRef.orderBy("state").orderBy("population", "desc")
Swift
citiesRef
    .order(by: "state")
    .order(by: "population", descending: true)
Objective-C
[[citiesRef queryOrderedByField:@"state"] queryOrderedByField:@"population" descending:YES];
  
Java
Android
citiesRef.orderBy("state").orderBy("population", Direction.DESCENDING);
Kotlin
Android
citiesRef.orderBy("state").orderBy("population", Query.Direction.DESCENDING)
Java
Query query = cities.orderBy("state").orderBy("population", Direction.DESCENDING);
Python
cities_ref = db.collection(u'cities')
cities_ref.order_by(u'state').order_by(
    u'population', direction=firestore.Query.DESCENDING)
Node.js
var byStateByPop = citiesRef.orderBy('state').orderBy('population', 'desc');
Go
query := client.Collection("cities").OrderBy("state", firestore.Asc).OrderBy("population", firestore.Desc)
PHP
$query = $citiesRef->orderBy('state')->orderBy('population', 'DESC');
C#
Query query = citiesRef.OrderBy("State").OrderByDescending("Population");
Ruby
query = cities_ref.order("state").order("population", "desc")

Combine os filtros where() a orderBy() e limit(). No exemplo a seguir, as consultas definem um limite de preenchimento, ordenam esse valor em ordem crescente e retornam apenas os primeiros resultados que excedem o limite:

Web
citiesRef.where("population", ">", 100000).orderBy("population").limit(2)
Swift
citiesRef
    .whereField("population", isGreaterThan: 100000)
    .order(by: "population")
    .limit(to: 2)
Objective-C
[[[citiesRef queryWhereField:@"population" isGreaterThan:@100000]
    queryOrderedByField:@"population"]
    queryLimitedTo:2];
  
Java
Android
citiesRef.whereGreaterThan("population", 100000).orderBy("population").limit(2);
Kotlin
Android
citiesRef.whereGreaterThan("population", 100000).orderBy("population").limit(2)
Java
Query query = cities.whereGreaterThan("population", 2500000L).orderBy("population").limit(2);
Python
cities_ref = db.collection(u'cities')
query = cities_ref.where(
    u'population', u'>', 2500000).order_by(u'population').limit(2)
results = query.get()
Node.js
var biggest = citiesRef.where('population', '>', 2500000)
  .orderBy('population').limit(2);
Go
query := cities.Where("population", ">", 2500000).OrderBy("population", firestore.Desc).Limit(2)
PHP
$query = $citiesRef
    ->where('population', '>', 2500000)
    ->orderBy('population')
    ->limit(2);
C#
Query query = citiesRef
    .WhereGreaterThan("Population", 2500000)
    .OrderBy("Population")
    .Limit(2);
Ruby
query = cities_ref.where("population", ">", 2_500_000).order("population").limit(2)

No entanto, se você tiver um filtro com uma comparação de intervalo (<, <=, >, >=), a primeira ordenação precisará estar no mesmo campo:

Válido: filtro de intervalo e orderBy no mesmo campo.

Web
citiesRef.where("population", ">", 100000).orderBy("population")
Swift
citiesRef
    .whereField("population", isGreaterThan: 100000)
    .order(by: "population")
Objective-C
[[citiesRef queryWhereField:@"population" isGreaterThan:@100000]
    queryOrderedByField:@"population"];
  
Java
Android
citiesRef.whereGreaterThan("population", 100000).orderBy("population");
Kotlin
Android
citiesRef.whereGreaterThan("population", 100000).orderBy("population")
Java
Query query = cities.whereGreaterThan("population", 2500000L).orderBy("population");
Python
cities_ref = db.collection(u'cities')
query = cities_ref.where(
    u'population', u'>', 2500000).order_by(u'population')
results = query.get()
Node.js
citiesRef.where('population', '>', 2500000).orderBy('population');
Go
query := cities.Where("population", ">", 2500000).OrderBy("population", firestore.Asc)
PHP
$query = $citiesRef
    ->where('population', '>', 2500000)
    ->orderBy('population');
C#
Query query = citiesRef
    .WhereGreaterThan("Population", 2500000)
    .OrderBy("Population");
Ruby
query = cities_ref.where("population", ">", 2_500_000).order("population")

Inválido: filtro de intervalo e primeiro orderBy em campos diferentes.

Web
citiesRef.where("population", ">", 100000).orderBy("country")
Swift
citiesRef
    .whereField("population", isGreaterThan: 100000)
    .order(by: "country")
Objective-C
[[citiesRef queryWhereField:@"population" isGreaterThan:@100000] queryOrderedByField:@"country"];
  
Java
Android
citiesRef.whereGreaterThan("population", 100000).orderBy("country");
Kotlin
Android
citiesRef.whereGreaterThan("population", 100000).orderBy("country")
Java
Query query = cities.whereGreaterThan("population", 2500000L).orderBy("country");
Python
cities_ref = db.collection(u'cities')
query = cities_ref.where(u'population', u'>', 2500000).order_by(u'country')
results = query.get()
Node.js
citiesRef.where('population', '>', 2500000).orderBy('country');
Go
// 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)
PHP
$query = $citiesRef
    ->where('population', '>', 2500000)
    ->orderBy('country');
C#
Query query = citiesRef
    .WhereGreaterThan("Population", 2500000)
    .OrderBy("Country");
Ruby
query = cities_ref.where("population", ">", 2_500_000).order("country")