对数据进行排序并限制其数量

Firestore 提供了强大的查询功能，用于指定您要从集合中检索哪些文档。这些查询也可以与 get() 或 addSnapshotListener() 结合使用，如获取数据中所述。

对数据进行排序和限制其数量

默认情况下，查询按文档 ID 以升序检索所有符合查询条件的文档。您可以使用 orderBy() 指定数据的排序顺序，也可以使用 limit() 限制检索到的文档数量。

例如，您可以通过以下代码查询按字母顺序排列的前 3 个城市：

Web

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

Swift

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

Objective-C

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

Java
Android

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

Kotlin+KTX
Android

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

Java

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

Python

db.collection(u'cities').order_by(u'name').limit(3).stream()snippets.py

C++

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

Node.js

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

Go

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

PHP

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

Unity

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

C#

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

Ruby

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

您也可以按降序排序以获取最后 3 个城市：

Web

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

Swift

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

Objective-C

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

Java
Android

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

Kotlin+KTX
Android

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

Java

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

Python

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

C++

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

Node.js

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

Go

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

PHP

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

Unity

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

C#

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

Ruby

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

您还可以按多个字段排序。例如，如果您想要按州排序，并在每一个州按人口数量以降序排序，可使用以下代码：

Web

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

Swift

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

Objective-C

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

Java
Android

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

Kotlin+KTX
Android

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

Java

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

Python

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

C++

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

Node.js

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

Go

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

PHP

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

Unity

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

C#

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

Ruby

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

您可以将 where() 过滤条件与 orderBy() 和 limit() 结合使用。下例中的查询定义了一个人口数量阈值，并按人口数量升序显示超过该阈值的前几个结果：

Web

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

Swift

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

Objective-C

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

Java
Android

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

Kotlin+KTX
Android

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

Java

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

Python

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

C++

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

Node.js

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

Go

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

PHP

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

Unity

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

C#

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

Ruby

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

但是，如果您的过滤条件带有范围比较关系运算符（<、<=、>、>=），您的第一重排序必须针对同一个字段，请参阅下面的 orderBy() 限制列表。

限制

请注意 orderBy() 子句的以下限制：

orderBy() 子句也会针对是否存在给定字段进行过滤。不含给定字段的文档将不包括在结果集中。

如果您添加的过滤条件带有范围比较关系运算符（<、<=、>、>=），您的第一重排序必须针对同一个字段：

有效：范围过滤条件和 orderBy 针对的是同一个字段

Web

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

Swift

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

Objective-C

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

Java
Android

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

Kotlin+KTX
Android

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

Java

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

Python

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

Node.js

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

Go

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

PHP

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

Unity

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

C#

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

Ruby

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

无效：范围过滤条件和第一个 orderBy 针对的是不同字段

Web

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

Swift

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

Objective-C

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

Java
Android

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

Kotlin+KTX
Android

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

Java

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

Python

cities_ref = db.collection(u'cities')
query = cities_ref.where(u'population', u'>', 2500000).order_by(u'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

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)query.go

PHP

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

Unity

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

C#

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

Ruby

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

您不能按等式（=) 或 in 子句中包含的任何字段对查询进行排序。

对数据进行排序并限制其数量

对数据进行排序和限制其数量

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