add "create" operation

[hnguyen08]

I'd like to extend JSON Patch and add a new "create" operation. It is exactly like "add", except it will not replace an existing value at the requested path. It will be useful in situations in where a client wants to ensure that they are not overwriting a value set by another client.

This was a suggestion from an email thread with the RFC6902 authors:

I think you've got it right; you can't do it in a fine-grained way with json-patch. Of course, you could use HTTP conditionals (e.g., If-Match), but that's more coarse-grained.
If you want to do this right now, I think the best thing to do would be to define a new operation and then use a new media type to differentiate between it and JSON Patch.
I'd be interested in starting a new version of json patch if we can get enough experience with this one to make it worthwhile...

Although it deviates from the RFC, I think it would be useful for others to use, perhaps in a custom JsonPatch implementation as you mentioned in #9.

Let me know what you think!

[fge]

I agree that this operation is nice, but indeed I'd like to keep RFC 6902 compatibility, which means I'll need to refactor and make JsonPatch abstract... That'll be for a 2.0 version.

As to the patch itself, it looks good, but I'd suggest the following changes:

• renaming AddableOperation to AdditionOperation,
• add a boolean to its protected constructor which would be true if we wanted to overwrite object members,
• modify the code of addToObject() so that it exploit this boolean to know whether it should overwrite.

[hnguyen08]

Thanks! I'll make an update using your suggestions.

[hnguyen08]

Squashed

[hnguyen08]

Updated to make overwriteExisting final. Let me know what you think

[fge]

Excellent! Now I need to find the time to work on that project again... Right now I'm busy with json-schema-*...

[hnguyen08]

Thanks, I'll keep an eye out for any updates.