检索记录中已更新的字段

Question

Can I retrieve the fields that have been updated in a view? Ideally I would be able to retrieve the total number of fields that have been updated (item added to list field or field changed) and the names/count of the individual fields.

Given a db record such as:

{
    "_id": "e3cfb5e19e5c05fb6822c5ee228c4f2e",
    "_rev": "52-c78a26776b0e0736dd45e44a47634031",
    "last_updated": "23/04/2015",
    "title", "testdoc",
    "samples": [
        {
            "confidence": "high",
            "handle": "joetest"
        }
    ],
    "locations": [
        {"Toronto", "Ontario"},
        {"Vancouver", "British Columbia"}
    ]
}

If there are 2 new items in "samples" and 1 in "locations" I would see an updated count of 3.

Answer 1

Assuming you retrieve the data before it's updated, you can compare it to the data after it's updated. The following simple function looks at any keys with arrays in the original data and returns the length of the new data.

def list_delta(before, after):
    out = {}

    for key in before:
        if isinstance(before[key], list):
            out[key] = len(after[key]) - len(before[key])

    return out

before = {'name': 'davidism', 'numbers': [0, 1, 2, 3, 4]}
after = do_update(before)
# after = {'name': 'davidism', 'numbers': [0, 1, 2, 3, 4, 5]}
list_delta(before, after)
# returns {'numbers': 1}

You can get more clever and compare if keys were added or removed, or if the actual values changed, or do a deeper recursive comparison for nested structures, but that's beyond the scope of this answer.