rdblue commented on code in PR #6437:
URL: https://github.com/apache/iceberg/pull/6437#discussion_r1056513857
##########
python/pyiceberg/schema.py:
##########
@@ -1046,3 +1055,79 @@ def _project_map(map_type: MapType, value_result:
IcebergType) -> MapType:
value_type=value_result,
value_required=map_type.value_required,
)
+
+
+@singledispatch
+def promote(file_type: IcebergType, read_type: IcebergType) -> IcebergType:
+ """Promotes reading a file type to a read type
+
+ Args:
+ file_type (IcebergType): The type of the Avro file
+ read_type (IcebergType): The requested read type
+
+ Raises:
+ ResolveException: If attempting to resolve an unrecognized object type
+ """
+ raise ResolveException(f"Cannot promote {file_type} to {read_type}")
+
+
+@promote.register(IntegerType)
+def _(file_type: IntegerType, read_type: IcebergType) -> IcebergType:
+ if isinstance(read_type, LongType):
+ # Ints/Longs are binary compatible in Avro, so this is okay
+ return read_type
+ else:
+ raise ResolveException(f"Cannot promote an int to {read_type}")
+
+
+@promote.register(FloatType)
+def _(file_type: FloatType, read_type: IcebergType) -> IcebergType:
+ if isinstance(read_type, DoubleType):
+ # A double type is wider
+ return read_type
+ else:
+ raise ResolveException(f"Cannot promote an float to {read_type}")
+
+
+@promote.register(StringType)
+def _(file_type: StringType, read_type: IcebergType) -> IcebergType:
+ if isinstance(read_type, BinaryType):
+ return read_type
+ else:
+ raise ResolveException(f"Cannot promote an string to {read_type}")
+
+
+@promote.register(BinaryType)
+def _(file_type: BinaryType, read_type: IcebergType) -> IcebergType:
+ if isinstance(read_type, StringType):
+ return read_type
+ else:
+ raise ResolveException(f"Cannot promote an binary to {read_type}")
+
+
+@promote.register(DecimalType)
+def _(file_type: DecimalType, read_type: IcebergType) -> IcebergType:
+ if isinstance(read_type, DecimalType):
+ if file_type.precision <= read_type.precision and file_type.scale ==
file_type.scale:
+ return read_type
+ else:
+ raise ResolveException(f"Cannot reduce precision from {file_type}
to {read_type}")
+ else:
+ raise ResolveException(f"Cannot promote an decimal to {read_type}")
+
+
+@promote.register(StructType)
+def _(file_type: StructType, read_type: IcebergType) -> IcebergType:
Review Comment:
Do we need a struct implementation? Seems like this should only be for
primitives to keep the logic simple. Visitors can line up other types.
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