On 6/2/22 9:24 AM, bauss wrote:
On Thursday, 2 June 2022 at 08:27:32 UTC, Antonio wrote:
JSON properties can be
- a value
- null
- absent
What's the standard way to define a serialziable/deserializable
structs supporting properties of any of this 4 kinds?:
* int
* int | null
* int | absent
* int | null | absent
Whats the best library to manage this JSON requirements? (all the 4
cases)?
Thanks
null and absent should be treated the same in the code, it's only when
serializing you should define one or the other, if you need to have null
values AND absent values then attributing accordingly is the solution.
Which means deserialization only has value/null and serialization has
value/null by default, but can be opt-in to also have absent.
One common mistake I've seen with parsers in D is that fields are often
opt-out, instead of opt-in, which means you always have to declare all
fields in a json object, but that's a bad implementation. All fields
should be optional and only required when attributed.
An example:
```
struct A { int x; }
```
Should be able to be deserialized from this json:
```
{"x":100,"y":200}
```
However a lot of parsers in D do not support that. Instead you must
declare the y member as well like:
```
struct A { int x; int y; }
```
Any decent parser should not have that problem.
If a field is required then it should be determined by an attribute like:
```
struct A {
@JsonRequired int x;
@JsonRequired int y;
}
```
There are 3 situations:
1. field in json and struct. Obvious result.
2. field in json but not in struct.
3. field in struct but not in json.
In jsoniopipe, I handle 2 by requiring a UDA on the struct to ignore the
members:
https://github.com/schveiguy/jsoniopipe/blob/4fa5350ed97786e34612a755f7e857544c6f9512/source/iopipe/json/serialize.d#L50-L55
Or, you can provide a `JSONValue` member, which will contain all
unexpected members, that you can attribute with `@extras`:
https://github.com/schveiguy/jsoniopipe/blob/4fa5350ed97786e34612a755f7e857544c6f9512/source/iopipe/json/serialize.d#L38-L43
I handle 3 by requiring a UDA on the field:
https://github.com/schveiguy/jsoniopipe/blob/4fa5350ed97786e34612a755f7e857544c6f9512/source/iopipe/json/serialize.d#L26-L30
Otherwise it's an error.
I feel it's too loose to make a best effort, and leave the rest up to
initial values, or just ignore possibly important information during
parsing.
-Steve
