集合（输入阶段）

集合（输入阶段）

说明

返回指定集合中的所有文档。集合可以嵌套。

示例

Web

const results = await execute(db.pipeline()
  .collection("users/bob/games")
  .sort(field("name").ascending())
  );
test.firestore.js

Swift

let results = try await db.pipeline()
  .collection("users/bob/games")
  .sort([Field("name").ascending()])
  .execute()
PipelineSnippets.swift

Kotlin
Android

val results = db.pipeline()
    .collection("users/bob/games")
    .sort(field("name").ascending())
    .execute()
DocSnippets.kt

Java
Android

Task<Pipeline.Snapshot> results = db.pipeline()
    .collection("users/bob/games")
    .sort(field("name").ascending())
    .execute();
DocSnippets.java

Python

from google.cloud.firestore_v1.pipeline_expressions import Field

results = (
    client.pipeline()
    .collection("users/bob/games")
    .sort(Field.of("name").ascending())
    .execute()
)
firestore_pipelines.py

Java

Pipeline.Snapshot results =
    firestore
        .pipeline()
        .collection("users/bob/games")
        .sort(ascending(field("name")))
        .execute()
        .get();
PipelineSnippets.java

Go

snapshot := client.Pipeline().
	Collection("users/bob/games").
	Sort(firestore.Orders(firestore.Ascending(firestore.FieldOf("name")))).
	Execute(ctx)
pipeline_snippets_general.go

行为

如需使用 collection(...) 阶段，它必须作为流水线（或子流水线）中的第一个阶段出现。

从 collection(...) 阶段返回的文档顺序不稳定，不能依赖。Firestore 会尝试以尽可能高效的方式执行查询，这可能会根据架构或索引配置更改顺序。可使用后续的 sort(...) 阶段 来获得确定性的顺序。

例如，对于以下文档：

Node.js

await db.collection("cities").doc("SF").set({name: "San Francsico", state: "California"});
await db.collection("cities").doc("NYC").set({name: "New York City", state: "New York"});
await db.collection("cities").doc("CHI").set({name: "Chicago", state: "Illinois"});
await db.collection("states").doc("CA").set({name: "California"});

collection 阶段可用于检索 cities 集合中的所有城市，然后按名称升序对它们进行排序。

Node.js

const results = await db.pipeline()
  .collection("/cities")
  .sort(field("name").ascending())
  .execute();

此查询会生成以下文档：

  { name: "Chicago", state: "Illinois" }
  { name: "New York City", state: "New York" }
  { name: "San Francisco", state: "California" }

子集合

您还可以通过提供阶段的完整路径，使用 collection(...) 阶段来定位特定父级下的集合。

例如，对于以下文档：

Node.js

await db.collection("cities/SF/departments").doc("building").set({name: "SF Building Deparment", employees: 750});
await db.collection("cities/NY/departments").doc("building").set({name: "NY Building Deparment", employees: 1000});
await db.collection("cities/CHI/departments").doc("building").set({name: "CHI Building Deparment", employees: 900});
await db.collection("cities/NY/departments").doc("finance").set({name: "NY Finance Deparment", employees: 1200});

在此示例中，我们只希望获取纽约市的部门。

Node.js

const results = await db.pipeline()
  .collection("/cities/NY/departments")
  .sort(field("employees").ascending())
  .execute();

这将返回完整路径 cities/NY/departments 下的所有部门。

  { name: "NY Building Deparment", employees: 1000 }
  { name: "NY Finance Deparment", employees: 1200 }