After uploading a file to Cloud Storage reference, you can also get
and update the file metadata, for example to view or update the content type.
Files can also store custom key/value pairs with additional file metadata.
File metadata contains common properties such as
name
,
size
, and
contentType
(often referred to as MIME type) in addition to some less
common ones like
contentDisposition
and
timeCreated
. This metadata can be
retrieved from a Cloud Storage reference using
the
getMetadata()
method.
// Create reference to the file whose metadata we want to retrieve
final forestRef = storageRef.child("images/forest.jpg");
// Get metadata properties
final metadata = await forestRef.getMetadata();
// Metadata now contains the metadata for 'images/forest.jpg'
You can update file metadata at any time after the file upload completes by
using the
updateMetadata()
method. Refer to the
full list
for more information on what properties
can be updated. Only the properties specified in the metadata are updated,
all others are left unmodified.
// Create reference to the file whose metadata we want to change
final forestRef = storageRef.child("images/forest.jpg");
// Create file metadata to update
final newMetadata = SettableMetadata(
cacheControl: "public,max-age=300",
contentType: "image/jpeg",
);
// Update metadata properties
final metadata = await forestRef.updateMetadata(newMetadata);
// Updated metadata for 'images/forest.jpg' is returned
You can delete writable metadata properties by passing
null
:
// Delete the cacheControl property
final newMetadata = SettableMetadata(cacheControl: null);
final metadata = await forestRef.updateMetadata(newMetadata);
Handle Errors
There are a number of reasons why errors may occur on getting or updating
metadata, including the file not existing, or the user not having permission
to access the desired file. More information on errors can be found in the
Handle Errors
section of the docs.
You can specify custom metadata using the
customMetadata
parameter of the
SettableMetadata
constructor:
// Create reference to the file whose metadata we want to change
final forestRef = storageRef.child("images/forest.jpg");
// Create file metadata to update
final newCustomMetadata = SettableMetadata(
customMetadata: {
"location": "Yosemite, CA, USA",
"activity": "Hiking",
},
);
// Update metadata properties
final metadata = await forestRef.updateMetadata(newCustomMetadata);
// Updated metadata for 'images/forest.jpg' is returned
You can store app-specific data for each file in custom metadata, but we highly
recommend using a database (such as the
Firebase Realtime Database
) to store and synchronize this type of
data.
A full list of metadata properties on a file is available below:
Property
|
Type
|
Settable?
|
bucket
|
String
|
No
|
generation
|
String
|
No
|
metageneration
|
String
|
No
|
metadataGeneration
|
String
|
No
|
fullPath
|
String
|
No
|
name
|
String
|
No
|
size
|
int
|
No
|
timeCreated
|
DateTime
|
No
|
updated
|
DateTime
|
No
|
md5Hash
|
String
|
No
|
cacheControl
|
String
|
Yes
|
contentDisposition
|
String
|
Yes
|
contentEncoding
|
String
|
Yes
|
contentLanguage
|
String
|
Yes
|
contentType
|
String
|
Yes
|
customMetadata
|
Map<String, String>
|
Yes
|
Uploading, downloading, and updating files is important, but so is being able
to remove them. Let's learn how to
delete files
from Cloud Storage.