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.”

  • 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).

      • 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.

      • 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.

          •  masterspace   ( @masterspace@lemmy.ca ) 
            link
            fedilink
            English
            6
            edit-2
            5 months ago

            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.

              •  masterspace   ( @masterspace@lemmy.ca ) 
                link
                fedilink
                English
                3
                edit-2
                5 months ago

                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).

        •  lad   ( @sukhmel@programming.dev ) 
          link
          fedilink
          English
          15 months ago

          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

        • 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.

    •  bleistift2   ( @bleistift2@sopuli.xyz ) OP
      link
      fedilink
      English
      245 months ago

      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.

      https://en.wikipedia.org/wiki/Tony_Hoare

      • Huh, so Tony Hoare invented null and then Graydon Hoare invented Rust, immediately terminating the existence of null which does not have a traditional null value.

  • 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?

    •  Lysergid   ( @Lysergid@lemmy.ml ) 
      link
      fedilink
      6
      edit-2
      5 months ago

      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.

        • 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.

  • 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.