Metadata

iRODS offers metadata as key, value, units triplets. The type of the keys, values and units is always a string. Below we show how to create a Metadata object from a dataobject or collection.

The Metadata object

from ibridges.interactive import interactive_auth
from ibridges import IrodsPath

session = interactive_auth()
meta = IrodsPath(session, "~", "collection_or_dataobject").meta

With the object meta we can now access and manipulate the metadata of the data object.

Add metadata

To add metadata, you always need to provide a key and a value, the unit is optional and can be left out.

meta.add('NewKey', 'NewValue', 'NewUnit')
print(meta)

Note

You can have several metadata entries with the same key but different values and units, i.e. metadata keys are not unique in iRODS but the combination of key, value and unit must be unique.

Set metadata

The MetaData.set() method differs from the add method by removing all other entries with the same key first. This mirrors the implementation of the iCommands imeta set.

meta.set('ExistingKey', 'Value', 'Unit')

Delete metadata

Below are examples on how to delete metadata entries:

# Delete all entries with key 'NewKey'
meta.delete('NewKey')

# Delete all entries with key 'NewKey' and value 'NewValue'
meta.delete('NewKey', 'NewValue')

# Delete all entries with key 'NewKey' and units 'NewUnit'
meta.delete('NewKey', units='NewUnit')

# Delete a single entry with exactly that triplet.
meta.delete('NewKey', 'NewValue', 'NewUnit')

Export Metadata

The method MetaData.to_dict() will provide you with a python dictionary containing the user-defined metadata:

meta.to_dict()

{
'name': '<obj_name>',
'irods_id': 24490075,
'checksum': 'sha2:XGiECYZOtUfP9lnCGyZaBBkBGLaJJw1p6eoc0GxLeKU=',
'metadata': [('Key', 'Value', 'Unit'), ('Key', 'Value', 'Unit1')]
}

The dictionary contains the name of the data object or collection and its iRODS identifier. For data objects the checksum is also listed under the key checksum. The checksum is not calculated, but extracted from the iRODS database.

The user-defined metadata can be accessed with the key metadata.