IntegrityError: (psycopg2.errors.ForeignKeyViolation) update or delete on table "dataset" violates foreign key constraint "dataset_id_fk_dataset" on table "dataset_snapshot" DETAIL: Key (id)=(cd8ecd20-2fdc-4f5e-ba07-c27a3f0bd060) is still referenced from table "dataset_snapshot".

The entire reason of having a snapshot was so that we could change the dataset and still know the contents of the dataset at the time that a model was trained. 

In this case I think that we should allow this field to be nullable. Also ties into AB-397, we need to decide what data we delete when a user deletes their account. If the dataset isn't used anywhere we could delete it, otherwise we should anonymise it.