Your files are stored in a Cloud Storage bucket. The files in this bucket are presented in a hierarchical structure, just like the file system on your local hard disk, or the data in the Firebase Realtime Database. By creating a reference to a file, your app gains access to it. These references can then be used to upload or download data, get or update metadata or delete the file. A reference can either point to a specific file or to a higher level node in the hierarchy.
If you've used the Firebase Realtime Database, these paths should seem very familiar to you. However, your file data is stored in Cloud Storage, not in the Realtime Database.
Create a Reference
In order to upload or download files, delete files, or get or update metadata, you must create a reference to the file you want to operate on. A reference can be thought of as a pointer to a file in the cloud. References are lightweight, so you can create as many as you need, and they are also reusable for multiple operations.
Create references from the
storage() service in your Firebase app.
This reference points to the root of your Cloud Storage bucket.
// 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();
You can create a reference to a location lower in the tree,
'images/space.jpg' by using the
child() method on an existing reference.
// 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"
Navigate with References
You can also use the
root properties to navigate up the
parent navigates up one level,
root navigates all the way to the top.
// 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
root can be chained together multiple times, as
each returns a reference. The exception is the
// 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;
You can inspect references to better understand the files they point to
bucket properties. These properties
get the full path of the file, the name of the file,
and the bucket the file is stored in.
// 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;
Limitations on References
Reference paths and names can contain any sequence of valid Unicode characters, but certain restrictions are imposed including:
- Total length of
reference.fullPathmust be between 1 and 1024 bytes when UTF-8 encoded.
- No Carriage Return or Line Feed characters.
- Avoid using
?, as these do not work well with other tools such as the Firebase Realtime Database or gsutil.
// 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;
Next, let's learn how to upload files to Cloud Storage.