How to update records only storing changes?

Solution

data = [{'cid': 1, ...}, {'cid': 2, ...}, {'cid': 3, ...}]
for item in data:  # type: dict
    cid = item['cid']
    json_hash = hash(json.dumps(data))
    # Record - let's say a model from db
    record = get_record_by_cid(cid)
    if not record:
        save_record(cid, item, json_hash)
        continue
    
    if record.json_hash != json_hash:
        update_record(cid, item, json_hash)