Under the current BIDS Specification, the field defining which fieldmaps are associated with each epi image are defined in the fieldmap. Accessing this information requires some kind of backwards logic and searching through all fieldmap metadata to find which ones correspond to a given file, my solution to this is moving the field to the epi image metadata in a new field like AssociatedFieldmaps or AssociatedDistortionmaps, meaning the information as to which fieldmap is associated with each image is easily accessible by calling that epi images metadata.

Original authors: @akimbler