Adding metadata to the new dataset

[nataliejpg]

If I use the dataset as created by

dataset = qc. new_data_set('results', specs=[some_paramspec])

then I can add metadata to it like:

dataset.add_metadata('measurement_notes', 'really warm today')

but if I use the Measurement object to create a dataset like:

analysis_meas = Measurement()
analysis_meas.register_parameter(some_parameter)
with analysis_meas.run() as datasaver:
    datasaver.add_result((some_parameter.name, 5))

Then I don't see how I am meant to add metadata as neither Measurement nor Datasaver have an easy way to access the dataset or to add metadata.

In a related note it would be great to have an example of adding metadata in the examples and similarly of retrieving it (minimally how to retrieve the snapshot should be there unless I'm missing something(?)).

@jenshnielsen @Dominik-Vogel @WilliamHPNielsen @cgranade

[astafan8]

Just to add some information about problems and danger of the add_metadata method:

Within the context manager, you can access the DataSet object via the datasaver object as datasaver.dataset (e.g. using "dataset" attribute of "datasaver"), and then you can call add_metadata method. However, this method is actually quite dangerous (for example, see https://github.com/QCoDeS/Qcodes/issues/898). So my suggestion would be to use it like dataset.add_metadata('snapshot', <your data regardless of its format/representation>) (note that for snapshots we use JSON, so I recommend you to also convert your metadata to JSON for consistency/convenience). The problem with this usage is that it will overwrite (!) the snapshot data of the station, which is absolutely not handy. So, ideally, first, the snapshot needs to be retrieved dataset.get_metadata('snapshot'), then converted to Python dict, then an extra metadata can be added, the result converted to JSON, and only then the complete thing should be written again via dataset.add_metadata('snapshot', <JSON representation of the whole metadata>). This is very ugly and cumbersome and error prone, but it is a recipe that you can use know if it is absolutely necessary.

So, in short, do not use add_metadata until QCoDeS properly implements it.

[mgunyho]

Has there been any work on this? I would very much like to add metadata to my runs.

[astafan8]

no yet. this hasn't got enough prio yet. But contributions are welcome.

[mgunyho]

Alright, I can try to look into this at some point, although I'm not that familiar with SQL.