History is free

You want every edit to remain a complete snapshot, and a title-only change must not rewrite the body. Dacite’s move: keep the previous document value (same hash) in a history vector; restore by installing that value again. Unchanged fields keep their content hash — you do not invent git.

This is the second claim-proving app in the roadmap.

You will:

1. Seed a note with a long body.
2. Change only the title and see the body hash stay put.
3. Restore an older snapshot by installing the same value again.

Prerequisites

• A clone of this repo (see Install)
• JDK 17+ and the Clojure CLI, or Node.js 18+ / babashka for the file store

The shape

The root is a notebook, not a bare document:

{"doc"     {"title" "…" "body" "…" "tags" […] "edited-at" n}
 "history" [previous-doc …]}

history is newest-previous first. A restore reuses a historical doc value — same hash, no rewrite. The library does not invent git; the app shows the recipe.

Domain code lives in dacite.examples.notes and uses only dacite.value. Bodies print with v/pr-str so a long string is not dumped into RAM.

Local file

cd impl/clojure
clojure -M:notes -- --reset show

Or from the repo root:

npm run notes -- --reset show
bb notes --reset show

Expected shape:

seeded new store at target/dacite-notes
title:      Welcome
edited-at:  0
tags:       intro
body:       "Dacite notes keep every snapshot…" (n chars)
doc:        <12 hex chars>
history:    0 previous
root:       <64 hex chars>

Edit, list, diff, restore:

clojure -M:notes -- set title Hello
clojure -M:notes -- add-tag demo
clojure -M:notes -- list
clojure -M:notes -- diff 0 1
clojure -M:notes -- restore 1

Version 0 is current, 1 is the previous snapshot, and so on. diff compares field hashes — a title-only edit reports title and edited-at, not body.

--path DIR selects the store directory. The same --url recipe as Persist and update a document works if the HTTP service is running.

Sharing bench

clojure -M:notes -- bench

Typical output:

sharing bench
  title-only:   +N nodes
  body-rewrite: +M nodes
  body shared after title edit: true

M is larger than N because the seed body is a real paragraph. The title-only path allocates a new title string, a new doc map, and a history conj. The body node is the same hash.

What this pulled

No dac->clj. History is a vector of documents in the same store.

Next

Large sequences stay cheap — page with subvec; do not seq the whole log.