Kriskras99 opened a new issue, #517:
URL: https://github.com/apache/avro-rs/issues/517
Original issues #449 and #458 by @PookieBuns
Currently the `SchemaAware(De)Serializer` implementations only support one
representation of `Option<T>`: `["null", T::get_schema()]` (order of `null` and
`T` does not matter). This means that the following schema:
```json
[
"null",
"int",
"string"
]
```
can only map to the following enum:
```rust
enum Example {
Null,
Int(i32),
String(String),
}
```
It is requested that the following `Option` would also match this schema:
```rust
enum Example {
Int(i32),
String(String),
}
Option<Example>
```
This would require the following changes to the serializer:
1. In `serialize_some` and `serialize_none`: Only require that the current
schema is a `Schema::Union` with a `Schema::Null` variant
2. In `serialize_some` there are two cases to keep in mind:
- If there are only two variants, serialize using the current
implementation.
- If there are more variants, serialize `T` using the current union schema
but provide a flag to the serializer that the `null` variant cannot be used. It
would be preferable to modify the union schema/create a new union schema so
that the `null` variant does not exist, but as we need a reference to the
schema that would mean using a `Cow<Schema>` everywhere.
3. In `get_resolved_union_variant` the logic needs to be modified to correct
the index:
- If the index is before the `null` variant, it can be used as is
- If the index is at or after the `null` variant, the index needs to be
incremented by one
4. `UnionSerializer` would also need to be changed to ignore the null
variant when the flag is set
This would require the following changes to the deserializer:
1. In `deserialize_option`:
- Only require that the current schema is a `Schema::Union` with a
`Schema::Null` variant
- If a `null` is read, then the current logic can be used
- Otherwise, store the index that was read and `visit_some` with the
current deserializer
2. In `with_union` reading the index must be skipped if the index is already
set.
3. In `deserialize_enum` the `UnionEnumDeserializer` must be provided with
the stored index
4. In `UnionEnumDeserializer::variant_seed` the stored index must be used if
available
This would require the `AvroSchemaComponent` implementation for `Option<T>`
to only panic if `T::get_schema` is a union with a `Schema::Null` variant,
otherwise modify that schema to include `Schema::Null`.
There is probably more changes needed, but this is what I can think of right
now.
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