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.
Get 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'
Update File Metadata
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.
Custom Metadata
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.
File Metadata Properties
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.
