json_merge_patch

A Dart implementation of RFC 7396 — JSON Merge Patch.

Features

• mergePatch(target, patch) — Apply a merge patch to a JSON value.
• generate(source, target) — Create a merge patch that turns source into target.
• No external dependencies.
• Dart 3.0+.
• Passes all 16 test cases from RFC 7396 Appendix A.

Install

dart pub add json_merge_patch

Usage

import 'package:json_merge_patch/json_merge_patch.dart';

void main() {
  // Apply a merge patch
  final target = {'a': 'b', 'c': {'d': 'e', 'f': 'g'}};
  final patch = {'a': 'z', 'c': {'f': null}};
  final result = mergePatch(target, patch);
  print(result); // {a: z, c: {d: e}}

  // Generate a merge patch
  final source = {'a': 'b', 'c': 'd'};
  final goal = {'a': 'z', 'e': 'f'};
  final generated = generate(source, goal);
  print(generated); // {a: z, c: null, e: f}
}

How it works

RFC 7396 defines a recursive algorithm for partial JSON updates:

• If the patch is an object, merge it recursively with the target.
• If a patch value is null, remove that key from the target.
• If the patch is not an object, replace the target entirely.

Arrays are always replaced wholesale (not merged element-by-element), and null cannot be set as a value — it always means "delete".

Limitations

These come from the RFC 7396 spec itself:

• null means delete — you can't set a field's value to null.
• No array merging — arrays are replaced entirely.
• No conditional updates — there's no test operation like RFC 6902.

If you need those, see rfc_6902.

RFC compliance

Implements the MergePatch algorithm from RFC 7396 Section 2. All 16 Appendix A test cases are included and pass.

License

MIT. See LICENSE.

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