Consider implementing a version of update! that uses cursors. reducible-update!?

[camsaul]

Use a cursor to iterate over matching rows and then use a Clojure function to apply updates. If the fn returns nil (or the original map, with no changes?) then we can skip the update.

We can have similar versions for delete (f can decide to skip the delete?)

The before and after stuff would be easy to implement on top of these.

[camsaul]

1. Iterate over matching rows
2. Apply before-update to row + changes
3. for each column in the changes, call .updateObject or equivalent