SuKi2cn commented on code in PR #373:
URL: https://github.com/apache/iceberg-cpp/pull/373#discussion_r2583355826
##########
src/iceberg/expression/aggregate.cc:
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@@ -38,6 +40,58 @@ std::shared_ptr<PrimitiveType> GetPrimitiveType(const
BoundTerm& term) {
return internal::checked_pointer_cast<PrimitiveType>(term.type());
}
+Result<Scalar> LiteralToScalar(const Literal& literal) {
+ if (literal.IsNull()) {
+ return Scalar{std::monostate{}};
+ }
+
+ switch (literal.type()->type_id()) {
+ case TypeId::kBoolean:
+ return Scalar{std::get<bool>(literal.value())};
+ case TypeId::kInt:
+ case TypeId::kDate:
+ return Scalar{std::get<int32_t>(literal.value())};
+ case TypeId::kLong:
+ case TypeId::kTime:
+ case TypeId::kTimestamp:
+ case TypeId::kTimestampTz:
+ return Scalar{std::get<int64_t>(literal.value())};
+ case TypeId::kFloat:
+ return Scalar{std::get<float>(literal.value())};
+ case TypeId::kDouble:
+ return Scalar{std::get<double>(literal.value())};
+ case TypeId::kString: {
+ const auto& str = std::get<std::string>(literal.value());
+ return Scalar{std::string_view(str)};
+ }
+ case TypeId::kBinary:
+ case TypeId::kFixed: {
+ const auto& bytes = std::get<std::vector<uint8_t>>(literal.value());
+ return Scalar{
+ std::string_view(reinterpret_cast<const char*>(bytes.data()),
bytes.size())};
+ }
+ case TypeId::kDecimal:
+ return Scalar{std::get<Decimal>(literal.value())};
+ default:
+ return NotSupported("Cannot convert literal of type {} to Scalar",
+ literal.type()->ToString());
+ }
+}
+
+class SingleValueStructLike : public StructLike {
+ public:
+ explicit SingleValueStructLike(Literal literal) :
literal_(std::move(literal)) {}
+
+ Result<Scalar> GetField(size_t /*pos*/) const override {
Review Comment:
> Should we return error if pos is not 0?
I moved `LiteralToScalar`/`SingleValueStructLike` into `row/struct_like` as
the small adapter we use when evaluating aggregates from file metrics. I
originally tried to return an error when `pos != 0`, but that breaks the
metrics aggregation path: bound terms carry the original field position (often
1,2,…) so `Count`/`Max`/`Min` on file metrics all fail (ctest reproduces this).
The Java equivalent `ValueAggregate`
([ValueAggregate](https://github.com/apache/iceberg/blob/main/api/src/main/java/org/apache/iceberg/expressions/ValueAggregate.java#L60-L68))
also ignores the index for the same reason. It isn’t a reusable general
StructLike; it’s a narrow, internal adapter, so I think we need to ignore the
incoming index here for correctness. If anything in my understanding is off,
please let me know.
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