在網路上建立 Cloud Storage 參考資料

檔案會儲存在 Cloud Storage 值區中。這個值區中的檔案會以階層結構呈現，就像本機硬碟上的檔案系統，或 Firebase Realtime Database 中的資料一樣。建立檔案參照後，應用程式就能取得檔案存取權。這些參照項目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，也可以指向階層中較高層級的節點。

如果您曾使用 Firebase Realtime Database，這些路徑應該會讓您覺得很熟悉。不過，您的檔案資料會儲存在 Cloud Storage 中，而不是 Realtime Database 中。

可建立參照

如要上傳或下載檔案、刪除檔案，或取得或更新中繼資料，您必須建立要操作檔案的參照。您可以將參照視為指向雲端檔案的指標。參照是輕量資源，因此您可以視需要建立多個參照，而且還可用於多項作業。

如要建立參照，請使用 getStorage() 取得 Storage 服務的執行個體，然後以服務做為引數呼叫 ref()。這個參照會指向 Cloud Storage 儲存桶的根目錄。

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

您可以建立對樹狀結構中較低位置的參照，例如在呼叫 ref() 時，將這個路徑做為第二個引數傳入，以便建立 'images/space.jpg' 的參照。

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

使用參照導覽

您也可以使用 parent 和 root 屬性向上瀏覽檔案階層。parent 會向上一層瀏覽，而 root 會一直瀏覽至頂端。

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 可以連結多次，因為每個都會傳回參照。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，進一步瞭解參照所指向的檔案。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

參考資料限制

參照路徑和名稱可包含任何有效的 Unicode 字元序列，但有以下限制：

1. 以 UTF-8 編碼時，reference.fullPath 的總長度必須介於 1 到 1024 個位元組之間。
2. 不得使用回車或換行字元。
3. 請避免使用 #、[、]、* 或 ?，因為這些工具無法與其他工具 (例如 Firebase Realtime Database 或 gsutil) 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。