datalad.api.meta_aggregate(dataset=None, path=None)

Aggregate metadata of one or more sub-datasets for later reporting.


MetadataRecord storage is not forced to reside inside the datalad repository of the dataset. MetadataRecord might be stored within the repository that is used by a dataset, but it might as well be stored in another repository (or a non-git backend, once those exist). To distinguish metadata storage from the dataset storage, we refer to metadata storage as metadata-store. For now, the metadata-store is usually the git-repository that holds the dataset.


The distinction is the reason for the “double”-path arguments below. for each source metadata-store that should be integrated into the root metadata-store, we have to give the source metadata-store itself and the intra-dataset-path with regard to the root-dataset.

MetadataRecord aggregation refers to a procedure that combines metadata from different sub-datasets into a root dataset, i.e. a dataset that contains all the sub-datasets. Aggregated metadata is “prefixed” with the intra-dataset-paths of the sub-datasets. The intra-dataset-path for a sub-dataset is the path from the top-level directory of the root dataset, i.e. the directory that contains the “.datalad”-entry, to the top-level directory of the respective sub-dataset.

Aggregate works on existing metadata, it will not extract meta data from data file. To create metadata, use the meta-extract command.

As a result of the aggregation, the metadata of all specified sub-datasets will be available in the root metadata-store. A datalad meta-dump command on the root metadata-store will therefore be able to process metadata from the root dataset, as well as all aggregated sub-datasets.


  • dataset (Dataset or None, optional) – Topmost dataset metadata will be aggregated into. If no dataset is specified, a dataset will be discovered based on the current working directory. MetadataRecord for aggregated datasets will contain a dataset path that is relative to the top-dataset. [Default: None]
  • path (sequence of str or None, optional) – PATH to a sub-dataset whose metadata shall be aggregated into the topmost dataset (ROOT_DATASET). [Default: None]
  • on_failure ({'ignore', 'continue', 'stop'}, optional) – behavior to perform on failure: ‘ignore’ any failure is reported, but does not cause an exception; ‘continue’ if any failure occurs an exception will be raised at the end, but processing other actions will continue for as long as possible; ‘stop’: processing will stop on first failure and an exception is raised. A failure is any result with status ‘impossible’ or ‘error’. Raised exception is an IncompleteResultsError that carries the result dictionaries of the failures in its failed attribute. [Default: ‘continue’]
  • result_filter (callable or None, optional) – if given, each to-be-returned status dictionary is passed to this callable, and is only returned if the callable’s return value does not evaluate to False or a ValueError exception is raised. If the given callable supports **kwargs it will additionally be passed the keyword arguments of the original API call. [Default: None]
  • result_renderer – select rendering mode command results. ‘tailored’ enables a command- specific rendering style that is typically tailored to human consumption, if there is one for a specific command, or otherwise falls back on the the ‘generic’ result renderer; ‘generic’ renders each result in one line with key info like action, status, path, and an optional message); ‘json’ a complete JSON line serialization of the full result record; ‘json_pp’ like ‘json’, but pretty-printed spanning multiple lines; ‘disabled’ turns off result rendering entirely; ‘<template>’ reports any value(s) of any result properties in any format indicated by the template (e.g. ‘{path}’, compare with JSON output for all key-value choices). The template syntax follows the Python “format() language”. It is possible to report individual dictionary values, e.g. ‘{metadata[name]}’. If a 2nd-level key contains a colon, e.g. ‘music:Genre’, ‘:’ must be substituted by ‘#’ in the template, like so: ‘{metadata[music#Genre]}’. [Default: ‘tailored’]
  • result_xfm ({'datasets', 'successdatasets-or-none', 'paths', 'relpaths', 'metadata'} or callable or None, optional) – if given, each to-be-returned result status dictionary is passed to this callable, and its return value becomes the result instead. This is different from result_filter, as it can perform arbitrary transformation of the result value. This is mostly useful for top- level command invocations that need to provide the results in a particular format. Instead of a callable, a label for a pre-crafted result transformation can be given. [Default: None]
  • return_type ({'generator', 'list', 'item-or-list'}, optional) – return value behavior switch. If ‘item-or-list’ a single value is returned instead of a one-item return value list, or a list in case of multiple return values. None is return in case of an empty list. [Default: ‘list’]