"Can't use add op without position" adding properties to object

[withoutlogin]

Hi,

I think there's some kind of regression about following closed issue:
#6

With the latest npm version (1.0.0), I have following issue:

import * as jsonpatch from "fast-json-patch";
import toMongodb from "jsonpatch-to-mongodb";

const obj1 = { key: "value" };
const obj2 = { key: "value", newKey: "newValue" };
const patch = jsonpatch.compare(obj1, obj2); // [ { op: 'add', path: '/newKey', value: 'newValue' } ] 
toMongodb(patch); // throws: Unsupported Operation! can't use add op without position

As you can see patch is fully correct and should result with {$set: {newKey: "newValue"}}.

Thanks.

[mrcranky]

It looks like the new code assumes that adds are only ever adding values to arrays maybe?

Given how the spec is written, I'm not sure it's possible to write a complete Mongo update operation from just the patch document alone? Don't you need a copy of the target document so that you can test for whether or not the path targets properties which already exist, and whether or not they're objects / arrays?

[mrcranky]

Actually, for this case at least, it seems like the spec can be handled without knowledge of the target object. We're dealing with the second and third cases from https://tools.ietf.org/html/rfc6902#section-4.1:
o If the target location specifies an array index, a new value is
inserted into the array at the specified index.
o If the target location specifies an object member that does not
already exist, a new member is added to the object.
o If the target location specifies an object member that does exist,
that member's value is replaced.

Case 1 has been handled in the code, cases 2 and 3 both happen to map to $set, and that will have the desired effect regardless of whether or not the target location already exists. I'll see about making a pull request to cover this case.

[ddimitrioglo]

Any updates on this?
Facing the same issue.

[mrcranky]

When the PR wasn't accepted, I ended up going ahead and spending a day or so rolling our own module to do this, along the lines of my previous reply above; i.e. taking the existing document as an additional parameter so that operations can be applied with knowledge of the previous document. Sadly it is not open sourced, though I will ask if our company is okay with publishing it.

[ddimitrioglo]

@mrcranky that would be great!
Looking forward! 🤞 😉

[ratio91]

I have the same issue. would appreciate if you could share your solution @mrcranky. thanks!

[gadicc]

annual ping for @mrcranky to see if you were able to publish this 🙏 😁

[mrcranky]

annual ping for @mrcranky to see if you were able to publish this 🙏 😁

Okay, so, pre-empting the next annual ping, I have some positive news. I left my previous job, which never got around to giving the go-ahead, and so have had enough time to make https://www.npmjs.com/package/rfc6902-mongodb which is another attempt at the same functionality. It's my first npm module / github open source project, so if folks want to test it out, issues can be reported here and I'll see about fixing them.

[gadicc]

Ah amazing! Thanks so much, @mrcranky, and congrats on your first package! I'll check this out when I'm next working on the relevant package of mine... might be a while, but I've starred your repo in the meantime and thanks so much for reporting back and publishing! 🎉

[ddimitrioglo]

Thank you @mrcranky!
I'll definitely keep your new package in mind when I have some related work to do.

Regarding the first package - it's awesome!
Small note: do not include tests into the package, and think of using typescript, which would make the maintenance work much easier.
Anyway - good luck!