在網路上建立 Cloud Storage 參考資料

您的檔案會儲存在 Cloud Storage 值區中。這個值區中的檔案會以階層式結構呈現，如同本機硬碟中的檔案系統，或是 Firebase 即時資料庫中的資料。建立檔案的參照後，應用程式就能取得該檔案的存取權。這些參照便可用於上傳或下載資料、取得或更新中繼資料或刪除檔案。參照可以指向特定檔案，或是階層中更高層級的節點。

如果您已使用過 Firebase 即時資料庫，應該不太熟悉這些路徑。不過，檔案資料儲存在 Cloud Storage 中，而「不是」儲存在即時資料庫中。

可建立參照

如要上傳/下載檔案、刪除檔案，或是取得或更新中繼資料，您必須為要作業的檔案建立參照。參照可以視為雲端中檔案的指標，參照簡單，因此您可以視需要建立多個項目，同時也能重複用於多項作業。

如要建立參照，請使用 getStorage() 取得 Storage 服務的執行個體，然後針對服務做為引數呼叫 ref()。這項參考資源指向 Cloud Storage 值區的根目錄。

import { getStorage, ref } from "firebase/storage";

// Get a reference to the storage service, which is used to create references in your storage bucket
const storage = getStorage();

// Create a storage reference from our storage service
const storageRef = ref(storage);
storage_create_ref.js

// Get a reference to the storage service, which is used to create references in your storage bucket
var storage = firebase.storage();

// Create a storage reference from our storage service
var storageRef = storage.ref();
create-reference.js

如要建立樹狀結構中較低位置的參照，例如 'images/space.jpg'，請在呼叫 ref() 時，將此路徑做為第二個引數傳入。

import { getStorage, ref } from "firebase/storage";

const storage = getStorage();

// Create a child reference
const imagesRef = ref(storage, 'images');
// imagesRef now points to 'images'

// Child references can also take paths delimited by '/'
const spaceRef = ref(storage, 'images/space.jpg');
// spaceRef now points to "images/space.jpg"
// imagesRef still points to "images"
storage_create_ref_child.js

// Create a child reference
var imagesRef = storageRef.child('images');
// imagesRef now points to 'images'

// Child references can also take paths delimited by '/'
var spaceRef = storageRef.child('images/space.jpg');
// spaceRef now points to "images/space.jpg"
// imagesRef still points to "images"
create-reference.js

使用參考資料進行導覽

您也可以使用 parent 和 root 屬性向上瀏覽檔案階層。parent 會向上瀏覽一個層級，而 root 則會導覽至頂部。

import { getStorage, ref } from "firebase/storage";

const storage = getStorage();
const spaceRef = ref(storage, 'images/space.jpg');

// Parent allows us to move to the parent of a reference
const imagesRef = spaceRef.parent;
// imagesRef now points to 'images'

// Root allows us to move all the way back to the top of our bucket
const rootRef = spaceRef.root;
// rootRef now points to the root
storage_navigate_ref.js

// Parent allows us to move to the parent of a reference
var imagesRef = spaceRef.parent;
// imagesRef now points to 'images'

// Root allows us to move all the way back to the top of our bucket
var rootRef = spaceRef.root;
// rootRef now points to the root
create-reference.js

child()、parent 和 root 可以多次鏈結，因為各自會傳回參照。例外狀況是 root 的 parent，也就是 null。

import { getStorage, ref } from "firebase/storage";

const storage = getStorage();
const spaceRef = ref(storage, 'images/space.jpg');

// References can be chained together multiple times
const earthRef = ref(spaceRef.parent, 'earth.jpg');
// earthRef points to 'images/earth.jpg'

// nullRef is null, since the parent of root is null
const nullRef = spaceRef.root.parent;
storage_navigate_ref_chain.js

// References can be chained together multiple times
var earthRef = spaceRef.parent.child('earth.jpg');
// earthRef points to 'images/earth.jpg'

// nullRef is null, since the parent of root is null
var nullRef = spaceRef.root.parent;
create-reference.js

參照屬性

您可以使用 fullPath、name 和 bucket 屬性檢查參照，進一步瞭解指向的檔案。這些屬性會取得檔案的完整路徑、檔案名稱，以及檔案儲存的值區。

import { getStorage, ref } from "firebase/storage";

const storage = getStorage();
const spaceRef = ref(storage, 'images/space.jpg');

// Reference's path is: 'images/space.jpg'
// This is analogous to a file path on disk
spaceRef.fullPath;

// Reference's name is the last segment of the full path: 'space.jpg'
// This is analogous to the file name
spaceRef.name;

// Reference's bucket is the name of the storage bucket where files are stored
spaceRef.bucket;
storage_ref_properties.js

// Reference's path is: 'images/space.jpg'
// This is analogous to a file path on disk
spaceRef.fullPath;

// Reference's name is the last segment of the full path: 'space.jpg'
// This is analogous to the file name
spaceRef.name;

// Reference's bucket is the name of the storage bucket where files are stored
spaceRef.bucket;
create-reference.js

參考檔案的限制

參照路徑和名稱可包含任何序列的有效 Unicode 字元，但系統會設下某些限制：

1. 使用 UTF-8 編碼時，reference.fullPath 的總長度必須介於 1 到 1,024 個位元組。
2. 不得使用回車或換行字元。
3. 避免使用 #、[、]、* 或 ?，因為這些工具並不適合與 Firebase 即時資料庫或 gsutil 等其他工具搭配使用。

完整範例

import { getStorage, ref } from "firebase/storage";

const storage = getStorage();

// Points to the root reference
const storageRef = ref(storage);

// Points to 'images'
const imagesRef = ref(storageRef, 'images');

// Points to 'images/space.jpg'
// Note that you can use variables to create child values
const fileName = 'space.jpg';
const spaceRef = ref(imagesRef, fileName);

// File path is 'images/space.jpg'
const path = spaceRef.fullPath;

// File name is 'space.jpg'
const name = spaceRef.name;

// Points to 'images'
const imagesRefAgain = spaceRef.parent;
storage_ref_full_example.js

// Points to the root reference
var storageRef = firebase.storage().ref();

// Points to 'images'
var imagesRef = storageRef.child('images');

// Points to 'images/space.jpg'
// Note that you can use variables to create child values
var fileName = 'space.jpg';
var spaceRef = imagesRef.child(fileName);

// File path is 'images/space.jpg'
var path = spaceRef.fullPath;

// File name is 'space.jpg'
var name = spaceRef.name;

// Points to 'images'
var imagesRef = spaceRef.parent;
create-reference.js

接下來，我們將說明如何上傳檔案至 Cloud Storage。