sanity-diff-patch

Generates a set of Sanity patch mutations needed to change an item (usually a document) from one shape to another.

Most values will become simple set, unset or insert operations, but it will also (by default) try to use diff-match-patch for strings (read more).

An ifRevisionID constraint can be given to generate patches that include this revision as a safeguard, to prevent modifying documents that has changed since the diff was generated.

The document ID used in the patches is either extracted from item A and item B (_id property), or can be set explicitly by using the id option. This is required if the _id property differs in the two items, to prevent patching the wrong document.

If encountering undefined values within an array, they will be converted to null values and print a warning to the console. Should you want to remove undefined values from arrays, manually remove them from the array prior to diffing (array.filter(item => typeof item === 'undefined') is your friend).

Getting started

npm install --save sanity-diff-patch

Usage

import {diffPatch} from 'sanity-diff-patch'

const patch = diffPatch(itemA, itemB)
/*
[
  {patch: {id: 'docId', set: {...}}},
  {patch: {id: 'docId', unset: [...]}},
  {patch: {id: 'docId', insert: {...}}}
]
*/

Usage with mutations

import {diffPatch} from 'sanity-diff-patch'
import sanityClient from './myConfiguredSanityClient'

const itemA = {
  _id: 'die-hard-iii',
  _type: 'movie',
  _rev: 'k0k0s',
  name: 'Die Hard 3',
  year: 1995,
  characters: [
    {
      _key: 'ma4sg31',
      name: 'John McClane'
    },
    {
      _key: 'l13ma92',
      name: 'Simon Gruber'
    }
  ]
}

const itemB = {
  _id: 'drafts.die-hard-iii',
  _type: 'movie',
  name: 'Die Hard with a Vengeance',
  characters: [
    {
      _key: 'ma4sg31',
      name: 'John McClane'
    },
    {
      _key: 'l13ma92',
      name: 'Simon Grüber'
    }
  ]
}

// Specify id if the two documents do not match
const operations = diffPatch(itemA, itemB, {id: itemA._id, ifRevisionID: itemA._rev})
await sanityClient.transaction(operations).commit()

// Patches generated:
const generatedPatches = [
  {
    patch: {
      id: 'die-hard-iii',
      ifRevisionID: 'k0k0s',
      set: {
        'name': 'Die Hard with a Vengeance',
        'characters[_key=="l13ma92"].name': 'Simon Grüber'
      },
    }
  },
  {
    patch: {
      id: 'die-hard-iii',
      unset: ['year']
    }
  }
}

diff-match-patch

When encountering two strings to compare, this module will (by default) attempt to use diff-match-patch (DMP) to transition the string from one state to the next.

While these patches are extremely helpful (especially in a real-time, collaborative environment), they sometimes grow quite large and can be hard for humans to read. There are a few options you can use to tweak when this module will use these patches, and when to fall back to a regular set-patch instead.

The default rules says:

If the target string is below 30 characters long, don't use DMP
If the generated DMP is greater than 1.2 times larger than the target string, don't use DMP

To tune these rules, you can pass options to the differ:

import {diffPatch} from 'sanity-diff-patch'

diffPatch(itemA, itemB, {
  diffMatchPatch: {
    // Default is true, set to false to _always_ use `set`-patches
    enabled: true,

    // Only use diff-match-patch if target string is longer than this threshold
    lengthThresholdAbsolute: 30,

    // Only use generated diff-match-patch if the patch length is less than or equal to
    // (targetString * relative). Example: A 100 character target with a relative factor
    // of 1.2 will allow a 120 character diff-match-patch. If larger than this number,
    // it will fall back to a regular `set` patch.
    lengthThresholdRelative: 1.2
  }
})

In addition to these rules, there are certain cases where it will never use diff-match-patch:

If the patched key starts with an underscore (eg _type, _key, _ref)
If the diff-match-patch implementation cannot generate a legal patch due to unicode issues

Needs improvement

Improve patch on array item move
Improve patch on array item delete