What Is JSON Patch?
jsonpatch.com
jsonpatch.com
JSON Patch is not REST. It is not representational state. But it's also not the way any sane person has ever done RPC over HTTP. Typically RPCs accomplish mutation by just supplying whatever is the most ergonomic at the time; if you want to be able to rename an entity, you implement a /rename endpoint., etc.
In Javascript, there was always a normal, obvious way to handle Patch, which was to leverage null vs. undefined properties in javascript. However, in statically typed languages, people wanted to deserialize data into static types that don't support the concept of "undefined." This was the beginning of the end, because deserializing into a static type is actually a bug for an API that has an evolving schema. No longer can you distinguish between a null and undefined property if the a client omitted it.
So instead we end up with yet another preposterous proposed "standard" of Json patch, a completely insane and difficult to read instruction-set-over-json that is truly a hodgepodge.
Remember, mutations like this need to be assembled by the client. That means not only the code but also the user experience. The classic REST-like ways of doing these mutations originate in the "for free" usage of the HTML form element. That's gone, now you need some insane JsonPatcher library, and you need to somehow manipulate your UI around it.
I work in an industry of idiots.
I don't think it's as terrible as you describe. But I see your point. We can already do this kind of thing in many different ways that seem preferable over this.
Yeah, no, patch as you describe it is not a patch. Given this:
{field: [1,2,3]}
And given that two clients want to each add 4 and 5 respectively to the document, one will overwrite the other, which breaks the very principle of a patch since you end up with either [1,2,3,4] or [1,2,3,5] instead of [1,2,3,4,5] (or [1,2,3,5,4] depending on who was faster).
> I work in an industry of idiots.
Very true.
What? That sounds like you're not using a real db.
Imagine that you're using an app to manage customer information. For whatever reason you need to update Jane Doe. You pull up her records and start to make the change, but then realize you're late for a meeting. Afterwards, you finish your changes but you notice that someone accidentally entered her name as lowercase ("doe"), so you correct it and save. Cool! Except it isn't cool, because while you were in your meeting she called in to change her name because she got married and is now Jane Smith. You just reverted her back to Jane Doe. If the app included concurrency checks, it would've used something like the SQL Server rowversion column type or the Postgres xmin system column to detect that Jane's data had been modified after you loaded her user record, and you'd have gotten an error prompting you to refresh the page and make your changes again.
It's one of those things that happens a lot more often than you might think in the real world, but yet it's rare enough (or not considered a major problem) so that many apps get away with ignoring it entirely.
I think this really should be up to the client to decide what is required, since there will be cases where the 'nonconcurrent' behavior is in fact expected. In terms of HTTP that would be by using the If-Unmodified-Since header, but yes, it requires server side checks although one can be clever and use a common updated field on all resources.
The back end really has to make the determination of what resources need protection from concurrent updates and enforce it, because of the above and because if you're going to let the client decide whether or not to participate in concurrency checks you really end up with no protection at all.
0: https://developer.mozilla.org/en-US/docs/Web/HTTP/Headers/ET...
GET: {version: 1, field: [1,2,3]}
PATCH: {version: 1, field: [1,2,3,4]} # succeeds
PATCH: {version: 1, field: [1,2,3,5]} # fails with HTTP 409 response
# Client displays some sort of warning that the update failed, GETs the object again and merges the new state from the server with it's state and can retry the update
GET: {version: 2, field: [1,2,3,4]}
PATCH: {version: 2, field: [1,2,3,4,5]} # succeedsLikewise the moment you start to do this architecture is the moment you fail to scale. You're putting unnecessary load on your backend by forcing the client to refetch the resource in order to make another update, not to mention the scenario where a lot of clients are trying to add items to field
> GETs the object again and merges the new state from the server
At some critical point all those clients will start blocking each other as they constantly make PATCHes that fail and reGET only to fail again because another client managed to make their PATCH before them. The problem made worse by network latency and app code.
Patches that work with changesets will support a much higher concurrent write load as the concurrency/serialization is done server side, and the changesets will be small rather than the entire value. Under load all the individual requests may take longer to complete they will all ultimately succeed. Concurrency conflicts may still occur but they will be a couple orders of magnitude less frequent.
Depending on the type of update, eg. adding items to a list, this is what you want. Removing / updating values otoh may be classed as something you'd prefer to have constraint check via If- headers.
No, that's just a bug in your type.
data FieldPatch a
= Value a -- A value unmarshable to type `a` was given, apply patch
| SetToNull -- null was given, apply and patch to null
| Undefined -- field was not set, do not patch
| UnexpectedValue RawJSON -- optional, allows manual handling of unexpected types
Java supports sealed interfaces now, so this is not true anymore.
This is a perfectly reasonable take, although it fits well in systems otherwise generally more inclined to use HTTP semantics. I know that’s not REST, but it’s certainly easier to reason about and clearly document (eg OpenAPI) than its RPC analogues.
> But it's also not the way any sane person has ever done RPC over HTTP.
Why not?
Aside: I’ve also used it as a format for internal calls and change tracking. It’s surely not ideal, but it was already in the service and trivial to repurpose. Turned out to be an extremely lucky decision, as it also became a crucial tool for forensic analysis in a major recovery effort.
> I work in an industry of idiots.
You could just… not be a jerk. You have that option.
Anyway, I never did end up implementing an optimal "update card with ID 1234". If you edit a flashcard's front text, instead of updating the front text field alone, I ended up just writing out an entirely new copy of the flashcard in the journal (with the ID 1234 encoded). Super inefficient.
I was toying with the idea of coming up with a simpler format that does basically what this JSON patch does, where you an just encode "update object 1234's field foo.bar.baz to string ABC".
I figured I'd only need a handful of operations, to insert a new object, replace a node in an object's property tree given a key path, delete an object, append to an array property, etc.
If anyone has other solutions other than JSON Patch, I'd love to hear about them.
Apple Notes use’s CRDTs internally for exactly this.
Last year I experimented with an app architecture that used CouchDB/PouchDB for for synchronising data for a single user, multi device app. Then using Yjs to merge the conflicting edits - it worked incredible well.
If I had the time I would love to build a Yjs/CRDT native CouchDB like database that could use the Yjs state vectors as a wire protocol for syncing…
This is the very rough code behind the PouchDB/Yjs datastore. Effectively each Pouch/Couch document is actually "managed" by Yjs, all changes/operations via it. It then saves the binary Yjs blob as an attachment on the Pouch document with the current Yjs state exported as JSON for the main Pouch document. This gives you all the indexing/search you get with Pouch/Couch but with automatic merging of conflicting edits.
https://gist.github.com/samwillis/1465da23194d1ad480a5548458...
and a tread about it:
https://discuss.yjs.dev/t/distributed-offline-editing-with-c...
Ultimately though I don't think PouchDB is a good platform for this, building something that is native Yjs would be much better. If anyone is interested I would love to hear from them though!
Something that stands out immediately to me is that reliance on binary attachments. In my own CouchDB ecosystem work binary attachments have turned out to be just about the worst part of the ecosystem. PouchDB stores them pretty reliably, but every other CouchDB ecosystem database (Couchbase, Cloudant) including different versions of CouchDB itself (1.x is different from 2.x is different from 3.x in all sorts of ways) all have very different behavior when synchronizing attachments, the allowed size of attachments, the allowed types of attachments, the allowed characters in attachment names, and in general the sync protocol itself is prone to failures/timeouts with large attachments that are tough to work around because the break in the middle of replications. The number of times I've had to delete an attachment that PouchDB stored just fine to get a sync operation to complete with another server has been way too many already.
I've had to build bespoke attachment sync tools because I haven't been able to rely on attachments working in the CouchDB ecosystem.
Probably more evidence to back up your gut instinct that a native Yjs-oriented store may be better in the long term.
(Admittedly, too, I've been thinking that I need to replace the CouchDB ecosystem as a whole. PouchDB is great, but the flux I've seen in the Apache CouchDB project and the issues I've had with the managed service providers especially Cloudant after IBM makes it really hard to recommend the ecosystem. Overall it seems unhealthy/in-decline, which is sad when the core sync infrastructure seems so nice to work with when it works.)
I've built atleast 3 different specs for what could be described at JSON-Patch for different projects, and each has a slightly different semantic. eg. in one implementation someone suggested in another comment, instead of explicitly passing an "operation", I just pass "key": null and it gets interpreted as delete everything below this key. In another case "key": null and "key" not existing are treated as different cases etc.
TBH I'm glad that there's some form of standardization for this, but I wish it was more publicized so folks would stop building their own specs for this.
Genuinely curious how you troubleshoot JSON-Patch it feels like something that adds more mental overhead than it would be worth if it breaks. I understand how it would work in practice from a front-end perspective, I'm unsure about the backend though.
My issue is, if I know what's changed I rather just send the ID's and values that changed to the front-end at that stage, or just those records respectively.
Meanwhile, I'm actually not aware of any XML patch standard.
[
{ "op": "replace", "path": "/baz", "value": "boo" },
{ "op": "add", "path": "/hello/bim", "value": ["world"] },
{ "op": "remove", "path": "/foo" }
]
(patch
(replace (baz) "boo")
(add (hello bim) ("world"))
(remove (foo)))
And the s-expressions don't even solve the problem of terseness for wire-format reasons; protobufs beat them out in that category.
With that said, there's EDN and fressian which solve the problems mentioned.
In EDN you could encode an instruction like so for example `(replace :path "/foo" :value 1)`
This reads like a function call because it is a representation of a function call. The semantics are already there.
Even better you could use namespaced keywords and symbols where applicable and suddenly were in a world where we can convey context without nesting, out of bounds information/schema or funny string formats.
This is probably a personal-preference thing; speaking from years of slinging both JSON and elisp, I have to go to the docs to remember the contents of a JSON object far less often than I do to remember the relevant positional arguments to a defun.
The JSON could use positional syntax, since JSON has [ ] arrays, and that would reduce its clutter.
The S-exp could use keyword arguments; it would still be nicer. Note that if we do so, we still want the operation to be positionally determined; i.e. to be the first element.
(patch
(replace :path (baz) :value "boo")
(add :path (hello bim) :value ("world"))
(remove :path (foo)))
["op", {"kw1" : "arg", "kw2" : 3.1, ...}]I never claimed they weren't extensible. What you're describing as a feature I'm declaring a bug. Named syntaxes self-describe in a way positional syntaxes don't.
(... he says as his IDE helpfully kicks in to tell him what each of the twelve arguments to this auto-generated Java object constructor are in his source code... ;) ).
> JSON becomes even more verbose to achieve something like this
It doesn't because it has key-value pairs as a top-level construct via the object type. LISP represents those by creating positional local dependencies between positional arguments (which is a fine solution, but at that point they're equivalently verbose and if I go with the JSON approach I can take advantage of the JSON libraries already existing in the client and server of my web applications).
In an alternate universe where JavaScript had been just LISP, your approach would be great, but that ship sailed decades ago.
Yes you did because you claimed that it was an advantage of the original. The only purpose of such a remark would be to point out a contrast: extensibility is lost in Y, so I'm pointing out that X has it.
> Named syntaxes self-describe
That's nice but it doesn't connect with the extensibility point.
Named can make it easy to know which argument is serving which role, if you already understand the function and its arguments, where you would otherwise have to remember the argument positions: like which of two identically typed arguments is the destination of the data transfer, the other being source.
> It doesn't because it has key-value pairs as a top-level construct via the object type.
Yes, but this object has no order; there is no way to indicate the first element so you have to use a keyword to indicate the operator too. I believe I communicated this with the example.
My original claim was "The s-expression syntax's reliance on positional inputs is less self-describing and extension can only be done at the end of the s-expressions." You "solved" the issue of "positional inputs... less self-describing" by doubling the number of symbols in your s-expression example so that (with the exception of the first input) they are no longer positional. That doesn't actually solve the problem; it just demonstrates you can do named arguments in s-expressions too. Yes, of course you can; but why bother when my browser already supports JSON?
> That's nice but it doesn't connect with the extensibility point
Correct; they are two separate points. Positional inputs are less self-describing and also extension can only be done at the end of the s-expression. Two criticisms.
> there is no way to indicate the first element so you have to use a keyword to indicate the operator too
Technically, this is untrue; order doesn't matter since the operator can simply be any key that isn't already reserved. So `"add": true` would work to indicate an add stanza.
But I would not recommend this approach. I'd just instead do what the RFC does and specify the operator as another argument: `"op": "add"`. The advantage to this approach (unlike yours) is that, indeed, order does not matter; I do not need the operator name to be the first thing in the list.
The two approaches in the named-argument structure are just about equivalent, except that the JSON approach has the advantage that browsers already have built-in JSON support (which gives that format a huge practical advantage over introducing a novel s-expression format in this problem domain, unfortunately).
Actually, named arguments as such as an impediment to readability when you're already familiar with the API.
This is because they allow the order to be scrambled. No two invocations of the API have to use the same order, so you're always going to have to parse the names, which doubles the effort.
E.g. in C, memcpy(a, b, size) calls don't tell you which is the destination. But once you remember that it's the leftmost argument, it's moot., And it's better than dealing with six possible permutations:
memcpy(dst: a, src: b, size: s);
memcpy(src: b, dst: a, size: s);
memcpy(size: s, src: b, dst: a);
memcpy(size: s, dst: a, src: b);
memcpy(src: b, size: s, dst: a);
memcpy(dst: a, size: s, src: b);
memcpy(src: b, size: s, dst: a); // ERROR: the first argument of memcpy is not called "src".
(src: b, op: memcpy, ...) // 24 permutations!
Once you're reaching for keyword arguments, it means you have a bad API. The fixed, required positional parameters of an API are usually the only part that is designed. The optionals are often less so, and keywords are just a bag of ad hoc afterthoughts which only care about getting some needed effect.
Since I don't get that tooling for wire-protocol content(1), I prefer named properties there because the alternative is usually some nasty flavor of binary alignment or picking semantics out of a densely-packed forest of newline-stripped character streams. But the correct answer in an actual programming language is "Both. Your IDE should make it easy to toggle the names on and off for positional arguments."
If a dev house is already using JSON for all the reasons one might do so, the flat presentation given by the RFC is the right presentation. But the real correct answer is "match your tools to the problem and you don't have to trade off between brevity and clarity."
(1) unless I do. gRPC is a treat to work with because it's thin on-the-wire but the Chrome devtool extensions give you the context. It's not the right solution for the JSON patch protocol because, well, right there in the name... It's JSON. But it's the solution I'd actually recommend to a team putting something new together if they don't need to interface to the outside world / aren't concerned the outside world will balk at a basically binary-on-the-wire data format.
That's just one direction of "extensible". You can't remove existing arguments, which you can with named fields.
Removal isn't extension; so we are no longer on the topic of extensibility. For instance, it wouldn't be considered a compiler/vendor extension if the "for" statement were removed; it would be a (severe) nonconformance.
It may be easier to remove a named argument, if that argument is rarely used, because you can look for uses of that argument by name. If the hits are nonexistent to rare, you have very little work. In a public API, where you don't have access to all the code base which uses the function, you may not have any way of evaluating "rarely used" other than polling the user base.
Needless to say, a data format for a patch operation is a public API.You don't even control the software which implements an argument to be able to remove it. You can write some blurbs in the spec which declare something to be deprecated, and 20 years later, maybe everyone will have stopped using it and removed support.
/// Every `{ "type": "foo" }` object must have a `bar` field.
function foo(obj) {
if (obj.type === "foo") {
reticulate(obj.bar);
}
}
/// Relax requirement that every `{ "type": "foo" }` object must have a `bar` field.
function foo(obj) {
if (obj.type === "foo" && typeof obj.bar !== "undefined") {
reticulate(obj.bar);
}
}- "op", "path", "value"
- quotes around paths
- colons, commas
- curly braces
In exchange for parentheses.
More generally though, we have an isomorphism. If transformation between the forms is trivial, then use what form is more comfortable for you, but I think being able to identify the 'op' -> 'var-args' pairing is a good thing to keep an eye on. It's macros' bread and butter.
For the same reason
> If a person puts such a question to you as: ‘I have divided ten into two parts, and multiplying one of these by the other the result was twenty-one;’ then you know that one of the parts is thing and the other is ten minus thing.
is inferior to
> x(10-x)=21
The succinctness helps your brain focus on the important information so you don't get lost in the noise. If you find it hard to read at first, your brain can adapt to the patterns just fine.
> X times open parenthesis ten minus X close parenthesis equals twenty one
I'm not sure if your point is supposed to be that it's easier to understand if read another way or something, but no matter what the symbol version is the easiest for your brain (which is very good at pattern recognition) to see and pick up on.
Maybe I missed your point, so you'll have to be explicit.
By the way, I didn't contrive the example. I googled "before math notation" and chose it from the second result[1]. I had seen similar examples of what math looked like before notation, so I looked for an example.
[1] http://archive.boston.com/bostonglobe/ideas/brainiac/2014/06...
What's your actual point?
Most of the time the patch documents are not being written by a human anyway.
No, the original document should be S-expressions, too:
((baz . "qux")
(foo . "bar"))
"One hammer, and everything is a nail" sounds like a smorgasbord for malicious actors in a world where we know how often SQL injection and HTML injection proved to be common threat vectors (both being "trick the system into interpreting symbols that look the same in a different way" types of attacks). Imagine if all layers of the HTTP story had been the same language. Yikes.
This seems to happen constantly on HN:
Post: "Behold, a data format!"
Commenter: "This is just poorly implemented s-expressions!"
I did LISP in college. I had my moment of transcendence with it. So I get the fandom for it. But I don't get why people keep paraphrasing this one sentence over and over, yet absolutely no one uses s-expressions outside of LISP. The one person I know who uses LISP in the private sector (via Clojure which many people refuse to recognize as a LISP for some reason?) is being hired to do very academia type research and publish white papers about it. The rest of LISP users are quirky members of academia who complain endlessly about Python's prevalence.
It just kinda seems like if LISP or s-expressions were truly that great, there would be more convergence around it for expressing data structures.
Notice there is no JSX to define react components, just s-expressions.
(yes I know you can use React without JSX, but I think it's interesting that in a lisp there's not really much need to introduce something like JSX).
Anyway I think it's a neat example on how applicable s-expression are.
Not being at all versed in the LISP world myself might you or someone else share where the original quote came from?
Or alternatively Rebol, which was one of the inspirations to JSON.
With Rebol you could write these patches like this:
patch [
replace /baz: "boo"
add /hello: ["world"]
remove /foo
]
patch [
add /biscuits/1: [name: "Ginger Nut"]
] {patchset = [ ["+", "/hello", ["world"]], ["!", "/baz", "boo"], ["-", "/foo"] ]}
Diff is great as a middle tool but is not nearly as self-descriptive as modern protocols try to be.
Git was wise to copy diff for backwards compatibility with existing CLI tools because it is primarily accessed via command line. No such backwards-compatibility gain exists with a PATCH protocol over HTTP.
In terms of terseness: when servers care about terseness these days, they use a non-ASCII-on-the-wire transport like GRPC. I believe that is out of scope for this RFC.
(Personally, I would just push for request body compression. It's not common but it's not impossible, and then you get the best of both worlds. I bet the terse format compresses to roughly the same size as the verbose format.)
Here:
const [op, from, to] = patch
Edit: We could simplify this to five verbs by letting + take one or two arguments, where the 1adic form sets the value to null. I mean I wouldn't, but we could.
The Good:
1. Depending on your ORM or data access model, JSON patch is a fantastic option. If you’ve got existing services that can hand you deeply nested models, you can start writing PUT/PATCH routes that take JSON patch changesets and let it build things up automatically. Makes it as easy as checking a resource out of storage, applyPatch or applyOperation, check it back in.
2. You don’t really need to worry about bad types getting dumped into your base object, as you should be deferring type safety to the route DTO level anyway, and everything can trickle from there.
3. The ‘-‘ semantic works fine for signaling an intent to insert a new element.
4. 99% of the time the “protocol” seems to just work.
5. YMMV, but there’s a good chance that switching to JSON patch will let you delete front end code as well, since the front end models can in theory also use the very commands they pass to the back end to locally update models. It integrates very well with a redux pattern and seems like a base technology for undo/redo.
The Bad:
1. On the one hand ‘/‘ as the primary delimiter irks me. I suppose ‘.’ characters in a property name are more common than slashes, but still not my favorite. Furthermore, the escaped characters not using backslashes is weird. You write ~0 if you need to refer to ~ literally and ~1 for /, if I am not mistaken.
2. There’s a missing contextual mode for the ‘add’ op: creating missing objects along the path you’re talking about. For instance if your base object is {}, then add at path ‘/foo/bar’ will fail since foo is undefined. Should be a mode where I can say “yes, please create missing stuff along the way, thank you.”
“On the JSON patch, feel your GraphQL cravings subside in as little as thirty minutes!”
The op
{ “op”: “replace”, “path”: “/foo”, value { “a”: 3 } }
Applied to a base object
{ “foo”: { “a”: 0, “c”: 1 } }
Will update “a”, but will throw away existing property /foo/c.
This is dumb. The other problems like it are dumb. Like so dumb it’s hard to not ruminate, so everybody here that complains is right. But not much so that the technology is void of use as some seem to suggest.
It’s so funny that JSON Patch 2 hasn’t come out with more extensions/improvements. Perhaps this Ycomb thread is the little push over the edge that we need to get a ball rolling!
What is the behavior of your chosen library--mutable or immutable operations? I.e. do you pay the penalty of making a deeply nested copy of your scene graph for each turn?
Asking for a friend....
So far the favourite library is Fast-JSON-Patch[1]. The method we're trying is to build up a sequence of patches - so every object in the game can add a patch to the queue, and then once the system is ready, it can apply the patches and validate the result.
This particluar library allows the code to directly manipulate the object, and generate a patch from the changes made - so it keeps the code simple and easy to understand.
It worked really well, and our users had no problems making JSON Patch requests.
["foo","bar",1,"baz","quux"]
"/foo/bar/1/baz/quux"
At Notion, we use Array<string | number> as you suggest.
it's used in OpenAPI specs
apparently the goal was something that could be transferred in string contexts like a URI fragment, as well as JSON https://datatracker.ietf.org/doc/html/rfc6901#section-1
Arrays require some care to handle which is why I'm got some extensions in my client, but a super power that JSON patching enables is that it can be algebraic in nature. That it, we can define a patching which is associative (another extension where you preserve nulls) such that (X + da) + db = X + (da + db) = X + dc where da + db + dc
This allows you to leverage flow control when congestion happens (especially on mobile connections).
[{"op": "replace", "path":"/spec/template/metadata/annotations/restarted-at", "value": "'$(date -Iseconds)'"}]
to restart/redeploy.
Why not just send partial fields and handle it server side?
Not to mention its more data over the wire for small changes.
You have:
{
"baz": "qux",
"foo": "bar"
}
{
"baz": "boo"
}
You have a deeply nested property in a gigantic JSON document that you want to move, "why not just" send
{ "op": "move", "from": "/a/b/c/d", "path": "/a/b/c/e/f" }
{
"baz": "boo"
}
Another option, though, is to use the Range-Patch spec from: https://github.com/braid-org/braid-spec
For example: ElasticSearch can take a body on some GET requests, but many tools will not let you do this because a GET request should not have a body.
Append, insert at, remove, and remove at are more ambiguous.
won't that set a field called 'null', to the value null?
You can interpret a null field the same as a missing field. You only need to worry if you have arbitrary dictionary keys and need to differentiate a null value from an missing key.
Null != missing.
Not in the general case no, they are two different states, which may have entirely different semantics.
For instance a missing field can mean "don't touch this field" while a field set to null means "set this field to null".
Some schemas might opt to ignore this distinction and collapse the states, but that is a specific decision, and an express loss of information.
> You only need to worry if you have arbitrary dictionary keys and need to differentiate a null value from an missing key.
There are other situations where that's an issue, like the above, or when you're using the object as a set (which JSON doesn't have), or when you've defined the schema to never have missing fields (but possibly have some set to `null`) so clients will break, ...
{ "foo": null }
{ "foo": null }
the partial updates approach works ok for updating 'schemaful' data, where it could only ever mean to set the field to null and could never delete the field from the object altogether
but for editing a JSON document or other schemaless data then both operations are possible and you'd need to be able to distinguish them
I guarantee, another dev would come along, look at the custom spec, and think "Why not just use JSON Patch?"
I got around arrays by simply not needing them for the most part.
JSON Patch - https://datatracker.ietf.org/doc/html/rfc6902 JSON Pointer - https://datatracker.ietf.org/doc/html/rfc6901
Tried PR'ing to fix site, but repo didn't seem active
it contains XPath-style selectors and the ability to directly modify matched nodes in a Dict, including filtering (as indirect deletion) and upserts; the only thing that it's missing is sufficient addressability with regards to Lists (arrays), so I see myself building a similar 'op' processing but using jsonpath instead of jsonpatch language.
add one to the pile i guess
> Finally, if you need to refer to the end of an array you can use - instead of an index. For example, to refer to the end of the array of biscuits above you would use /biscuits/-
how do you refer to "this value" in this example?
{
"biscuits": {
"-": "this value"
"zzzz": "something else"
}
}Possibly because JSON already has them, so you need to further escape the escapes, which is difficult to author and read?
If you check out the implementations at the bottom of the post, you'll see that, at runtime, if biscuits is an object they index into `obj["-"]`. And if it's an array, they special-case "-" and index into `array[length]`.
i rather see they implement jsonpath - https://tools.ietf.org/id/draft-goessner-dispatch-jsonpath-0... instead of inventing their own xpath-like expression language tbh.
Edit: i suppose i shouldn't be surprised there's multiple standards to varying degrees of acceptance: https://datatracker.ietf.org/doc/html/rfc6901 so may be it is fine to use this expression language...
No, that’s specified in the JSON Pointer spec, which this spec depends on: https://datatracker.ietf.org/doc/html/rfc6901
> […] that's not fully specified by just the spec?
Specs depend on previous specs nearly all the time. Thank goodness for hyperlinks.
It also shows this in the Pointer spec.
- XML/XSLT
- JSON/JSONPatch
Textual diffs would only work if the starting point is guaranteed to be the same.
https://www.jvt.me/posts/2020/08/24/pretty-print-json-diff/
I'm also using a JSON-diff format in my data store[1], which is accumulated during insertions/updates/deletes in-memory and serialized during a commit, admittedly for large JSON instances (a few Gb and much more).
A lot of that comes down to internal application architecture. If you're working in Javascript / Typescript, where objects are inherently dictionaries / hashsets with ordering; yes, this is true. You will need to sort before serialization in order for the diff to be useful.
But: If you're working in a strongly-typed language like C# / Java / Rust / C++, and using an object -> JSON -> object serializer; the order of the elements is often quite explicit and never changes.
Also, there's no way to differentiate between deleting a key from an object and leaving it unchanged if you send a partial patch, assuming that `null` is a distinct value different than actually deleting the key itself.
For really simple use cases you don't need this but I've used something similar for an application where the JSON documents could get in the megabytes and it was a lifesaver.