reuvenlax commented on pull request #16947:
URL: https://github.com/apache/beam/pull/16947#issuecomment-1057270723
Unfortunately if you truly need recursive or mutually-recursive types, Beam
Schemas won't work today. We supported nested types, but not true recursion.
On Wed, Mar 2, 2022 at 10:40 AM Reuven Lax ***@***.***> wrote:
> Do you mean mutually recursive? We considered supporting this with schema,
> but the complexity was high and there didn't seem to be many good use
cases.
>
> On Wed, Mar 2, 2022 at 10:37 AM Moritz Mack ***@***.***>
> wrote:
>
>> But the getter methods are public, right?
>>
>> There's public getters of course, but not following the "getX" naming
>> convention.
>>
>> I've also looked briefly at just extending GetterBasedSchemaProvider,
>> that works really well actually. The read part is rather trivial. The
field
>> metadata of each SDK model provides an easy way to read fields (without
any
>> reflection involved).
>>
>> static class SdkFieldValueGetter<ObjectT, ValueT> implements
FieldValueGetter<ObjectT, ValueT> {
>> private final SdkField<ValueT> field;
>>
>> public SdkFieldValueGetter(SdkField<ValueT> field) {
>> this.field = field;
>> }
>>
>> @Override
>> @Nullable
>> public ValueT get(ObjectT object) {
>> return field.getValueOrDefault(object);
>> }
>>
>> @Override
>> public String name() {
>> return field.memberName();
>> }
>> }
>>
>> Recursive type hierarchies are also definitely support.
>>
>> Problem with recursive types is the immutable Schema. I'm not aware of
>> any way to generate such a schema for a recursive hierarchy ... same
>> problem exists for FieldValueTypeInformation.
>> Just verified it quickly, I get a stackoverflow as expected ... so
>> recursive types are definitely not supported.
>>
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