Ability to generate diff as merge patch

[dcokan]

Hi guys

I want to store a diffs between versions of a JSON. I can do it using collecting a diffs (RFC-6902). However with multiple changes I need to store big list of operations to be later applied. Since the library allows to apply merge patch to a JSON (RFC-7386) I think it would be very useful to be able to produce such merge patch having two JSONs. Is there a reason why it's not supported? Is it planned?

Thanks in advance

[torshid]

I was wondering the same thing. In my client application, I call a patch endpoint which expects a merge patch. I would like to generate this patch given the original data and the modified one (two json nodes). The API then applies the patch and persists the updated data.
The problem is that there is no way to generate this patch, although we can apply it if we previously created it in some way.

I wrote a method as follows, it may be useful for some (not sure if it complies completely to RFC-7386):

  public static ObjectNode diff(ObjectMapper mapper, ObjectNode original, ObjectNode modified) {

    ObjectNode result = mapper.createObjectNode();

    Iterator<String> iterator = modified.fieldNames();

    while (iterator.hasNext()) {

      String fieldName = iterator.next();

      JsonNode originalFieldNode = original.get(fieldName);
      JsonNode modifiedFieldNode = modified.get(fieldName);

      if (modifiedFieldNode.equals(originalFieldNode)) {
        continue;
      }

      if (!originalFieldNode.isNull() && modifiedFieldNode.isObject()) {
        result.set(fieldName, diff(mapper, originalFieldNode, modifiedFieldNode));
      } else {
        result.set(fieldName, modifiedFieldNode);
      }

    }

    return result;

  }

You may use it like that:

final JsonMergePatch patch =  JsonMergePatch.fromJson(diff(...));
final JsonNode patched = patch.apply(input);