Meme transcription: Panel 1. Two images of JSON, one is the empty object, one is an object in which the key name maps to the value null. Caption: “Corporate needs you to find the difference between this picture and this picture”
Panel 2. The Java backend dev answers, “They’re the same picture.”
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If you’re branching logic due to the existence or non-existence of a field rather than the value of a field (or treating undefined different from null), I’m going to say you’re the one doing something wrong, not the Java dev.
These two things SHOULD be treated the same by anybody in most cases, with the possible exception of rejecting the later due to schema mismatch (i.e. when a “name” field should never be defined, regardless of the value).
They’re semantically different for PATCH requests. The first does nothing, the second should unset the
namefield.Only if using JSON merge patch, and that’s the only time it’s acceptable. But JSON patch should be preferred over JSON merge patch anyway.
Servers should accept both null and undefined for normal request bodies, and clients should treat both as the same in responses. API designers should not give each bespoke semantics.
JSON patch is a dangerous thing to use over a network. It will allow you to change things inside array indices without knowing whether the same thing is still at that index by the time the server processes your request. That’s a recipe for race conditions.
That’s what the If-Match header is for. It prevents this problem.
That being said, I generally think
PUTs are preferable toPATCHes for simplicity.
Why?
Because Java struggles with basic things?
It’s absurd to send that much data on every patch request, to express no more information, but just to appease the shittiness of Java.
Why are you so ignorant?
Why not explaining instead of looking down on people? Now they know they’re wrong bit don’t know why. Nice.
You’ve replied to the wrong person.
Ya, having null semantics is one thing, but having different null and absent/undefined semantics just seems like a bad idea.
Not really, if absent means “no change”, present means “update” and null means “delete” the three values are perfectly well defined.
For what it’s worth, Amazon and Microsoft do it like this in their IoT offerings.
Zalando explicitly forbids it in their RESTful API Guidelines, and I would say their argument is a very good one.
Basically, if you want to provide more fine-grained semantics, use dedicated types for that purpose, rather than hoping every API consumer is going to faithfully adhere to the subtle distinctions you’ve created.
They’re not subtle distinctions.
There’s a huge difference between checking whether a field is present and checking whether it’s value is null.
If you use lazy loading, doing the wrong thing can trigger a whole network request and ruin performance.
Similarly when making a partial change to an object it is often flat out infeasible to return the whole object if you were never provided it in the first place, which will generally happen if you have a performance focused API since you don’t want to be wasting huge amounts of bandwidth on unneeded data.
The semantics of the API contract is distinct from its implementation details (lazy loading).
Treating null and undefined as distinct is never a requirement for general-purpose API design. That is, there is always an alternative design that doesn’t rely on that misfeature.
As for patches, while it might be true that JSON Merge Patch assigns different semantics to null and undefined values, JSON Merge Patch is a worse version of JSON Patch, which doesn’t have that problem, because like I originally described, the semantics are explicit in the data structure itself. This is a transformation that you can always apply.
No there isn’t.
Tell me how you partially change an object.
Object User :
{ Name: whatever, age: 0}
Tell me how you change the name without knowing the age. You fundamentally cannot, meaning that you either have to shuttle useless information back and forth constantly so that you can always patch the whole object, or you have to create a useless and unscalable number of endpoints, one for every possible field change.
As others have roundly pointed out, it is asinine to generally assume that undefined and null are the same thing, and no, it flat out it is not possible to design around that, because at a fundamental level those are different statements.
As I already said, it’s very simple with JSON Patch:
[ { *op": "replace", "path": "/Name™, "value": "otherName"} ]Good practice in API design is to permissively accept either undefined or null to represent optionality with same semantics (except when using JSON Merge Patch, but JSON Patch linked above should be preferred anyway).
This is also how it is defined in the JSON Merge Patch RFC.
it does feel ambiguous though as even what you outlined misses a 4th case. if null means delete, how do I update it to set the field to null?
It gets more fun if we’re talking SQL data via C API: is that 0 a field with 0 value or an actual NULL? Oracle’s Pro*C actually has an entirely different structure or indicator variables just to flag actual NULLs.
Except, if you use any library for deserialization of JSONs there is a chance that it will not distinguish between null and absent, and that will be absolutely standard compliant. This is also an issue with protobuf that inserts default values for plain types and enums. Those standards are just not fit too well for patching
I’ve never once seen a JSON serializer misjudge null and absent fields, I’ve just seen developers do that.
Well, Jackson before 2.9 did not differentiate, and although this was more than five years ago now, this is somewhat of a counter example
Also, you sound like serializers are not made by developers
Bruh, there’s a difference between the one or two serializing packages used in each language, and the thousands and thousands and thousands of developers who miscode contracts after that point.
Billion dollar mistake
For those who don’t know:
Speaking at a software conference in 2009, Tony Hoare hyperbolically apologized for “inventing” the null reference:[26] [27]
I call it my billion-dollar mistake. It was the invention of the null reference in 1965. At that time, I was designing the first comprehensive type system for references in an object oriented language (ALGOL W). My goal was to ensure that all use of references should be absolutely safe, with checking performed automatically by the compiler. But I couldn’t resist the temptation to put in a null reference, simply because it was so easy to implement. This has led to innumerable errors, vulnerabilities, and system crashes, which have probably caused a billion dollars of pain and damage in the last forty years.
Huh, so Tony Hoare invented
nulland then Graydon Hoare invented Rust,immediately terminating the existence ofwhich does not have a traditionalnullnullvalue.
Thanks for the transcription!
Surely Java can tell the difference between a key with a null value and the absence of that key, no?
I mean, you can set up your deserialization to handle nulls in different ways, but a string to object dictionary would capture this, right?
Sure, Java can tell the difference. But that doesn’t mean that the guy writing the API cares whether or not he adds a key to the dictionary before yeeting it to the client.
Kinda, I guess we all can agree it’s more typical to deserialize into POJO where theres is no such thing as missing field. Otherwise why would you choose Java if you don’t use types. This great precondition for various stupid hacks to achieve „patching” resources, like blank strings or negative numbers for positive-only fields or even Optional as a field.
You can always bind the JSON to a hashmap implementation, as that’s all JSON is anyway. It’s not pretty but it works.
It can, but especially during serialization Java sometimes adds null references to null values.
That’s usually a mistake by the API designer and/or Java dev, but happens pretty often.
That’s the thing though, isn’t it? The devs on either side are entering into a contract (the API) that addresses this issue, even if by omission. Whoever breaks the contract must rightfully be ejected into the stratosphere.
That’s exactly not the thing, because nobody broke the contract, they simply interpret it differently in details.
Having a null reference is perfectly valid json, as long as it’s not explicitly prohibited. Null just says “nothing in here” and that’s exactly what an omission also communicates.
The difference is just whether you treat implicit and explicit non-existence differently. And neither interpretation is wrong per contract.
I think we’re fully in agreement here: if the API doesn’t specify how to handle null values, that omission means they’re perfectly valid and expected.
Imagine a delivery company’s van exploding if somebody attempts to ship an empty box. That would be a very poorly built van.
Null means I’m telling you it’s null.
Omission means it’s not there and I’m not telling you anything about it.
There is a world of difference between those two statements. It’s the difference between telling someone you’re single or just sitting there and saying nothing.
I (think, at least) the point they’re making is that unless the API contract specifically differentiates between “present and null” and “absent” then there is no difference. (Specifically for field values.)
The point I’m making is kind of the opposite, unless the contract explicitly states that they’re the same they should not be treated as the same, because at a fundamental level they are not the same thing even if Java wants to treat them as such.
Nope.
If there’s a clear definition that there can be something, implicit and explicit omission are equivalent. And that’s exactly the case we’re talking about here.
Sure, in a specific scenario where you decide they’re equivalent they are, congratulations. They’re not generally.
Did you read the comments above?
You can’t just ignore context and proclaim some universal truth, which just happens to be your opinion.
I’m sad that there are people who call themselves developers who need to be told this.
Just what every programming language needs, not one, but two types of null! Because nobody ever said one type was difficult enough.
If I see any of you make this distinction matter for anything other than “PUT vs. PATCH” semantics I’m going to be very angry.
I do this constantly.
undefined: not retrieved yet.null: Error when retrieving. Makes it easy to reason about what the current state of the data is without the need for additional status flags.
Had to solve this with Go recently, which was not as straightforward as I’d hoped! https://www.jvt.me/posts/2024/01/09/go-json-nullable/
