iamwilhelm / cambria-project

Schema evolution with bi-directional lenses.

Cambria

Cambria is a Javascript/Typescript library for converting JSON data between related schemas.

You specify (in YAML or JSON) a lens, which specifies a data transformation. Cambria lets you use this lens to convert:

• a whole document, in JSON
• an edit to a document, in JSON Patch
• a schema description, in JSON Schema

Lenses are bidirectional. Once you've converted a document from schema A to schema B, you can edit the document in schema B and propagate those edits backwards through the same lens to schema A.

For more background on why Cambria exists and what it can do, see the research essay.

⚠ Cambria is still immature software, and isn't yet ready for production use

Use cases

• Manage backwards compatibility in a JSON API
• Manage database migrations for JSON data
• Transform a JSON document into a different shape on the command line
• Combine with cambria-automerge to collaborate on documents across multiple versions of local-first software

CLI Usage

Cambria includes a simple CLI tool for converting JSON from the command line.

(You'll want to run yarn build to compile the latest code.)

Covert the github issue into a an arthropod-style issue:

cat ./demo/github-issue.json | node ./dist/cli.js -l ./demo/github-arthropod.lens.yml

To get a live updating pipeline using entr:

echo ./demo/github-arthropod.lens.yml | entr bash -c "cat ./demo/github-issue.json | node ./dist/cli.js -l ./demo/github-arthropod.lens.yml > ./demo/simple-issue.json"

Compile back from an updated "simple issue" to a new github issue file:

cat ./demo/simple-issue.json | node ./dist/cli.js -l ./demo/github-arthropod.lens.yml -r -b ./demo/github-issue.json

Live updating pipeline backwards:

echo ./demo/simple-issue.json | entr bash -c "cat ./demo/simple-issue.json | node ./dist/cli.js -l ./demo/github-arthropod.lens.yml -r -b ./demo/github-issue.json > ./demo/new-github-issue.json"

API Usage

Cambria is mostly intended to be used as a Typescript / Javascript library. Here's a simple example of converting an entire document.

// read doc from stdin if no input specified
const input = readFileSync(program.input || 0, 'utf-8')
const doc = JSON.parse(input)

// we can (optionally) apply the contents of the changed document to a target document
const targetDoc = program.base ? JSON.parse(readFileSync(program.base, 'utf-8')) : {}

// now load a (yaml) lens definition
const lensData = readFileSync(program.lens, 'utf-8')
let lens = loadYamlLens(lensData)

// should we reverse this lens?
if (program.reverse) {
  lens = reverseLens(lens)
}

// finally, apply the lens to the document, with the schema, onto the target document!
const newDoc = applyLensToDoc(lens, doc, program.schema, targetDoc)
console.log(JSON.stringify(newDoc, null, 4))

Install

If you're using npm, run npm install cambria. If you're using yarn, run yarn add cambria. Then you can import it with require('cambria') as in the examples (or import * as Cambria from 'cambria' if using ES2015 or TypeScript).

Tests

npm run test