Fokko commented on code in PR #212: URL: https://github.com/apache/iceberg-python/pull/212#discussion_r1429740418
########## pyiceberg/table/name_mapping.py: ########## @@ -0,0 +1,203 @@ +# Licensed to the Apache Software Foundation (ASF) under one +# or more contributor license agreements. See the NOTICE file +# distributed with this work for additional information +# regarding copyright ownership. The ASF licenses this file +# to you under the Apache License, Version 2.0 (the +# "License"); you may not use this file except in compliance +# with the License. You may obtain a copy of the License at +# +# http://www.apache.org/licenses/LICENSE-2.0 +# +# Unless required by applicable law or agreed to in writing, +# software distributed under the License is distributed on an +# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY +# KIND, either express or implied. See the License for the +# specific language governing permissions and limitations +# under the License. +""" +Contains everything around the name mapping. + +More information can be found on here: +https://iceberg.apache.org/spec/#name-mapping-serialization +""" +from __future__ import annotations + +from abc import ABC, abstractmethod +from collections import ChainMap +from functools import cached_property, singledispatch +from typing import Any, Dict, Generic, List, TypeVar, Union + +from pydantic import Field, conlist, model_serializer + +from pyiceberg.schema import Schema, SchemaVisitor, visit +from pyiceberg.typedef import IcebergBaseModel, IcebergRootModel +from pyiceberg.types import ListType, MapType, NestedField, PrimitiveType, StructType + + +class MappedField(IcebergBaseModel): + field_id: int = Field(alias="field-id") + names: List[str] = conlist(str, min_length=1) + fields: List[MappedField] = Field(default_factory=list) + + @model_serializer + def ser_model(self) -> Dict[str, Any]: + """Set custom serializer to leave out the field when it is empty.""" + fields = {'fields': self.fields} if len(self.fields) > 0 else {} + return { + 'field-id': self.field_id, + 'names': self.names, + **fields, + } + + def __len__(self) -> int: + """Return the number of fields.""" + return len(self.fields) + + def __str__(self) -> str: + """Convert the mapped-field into a nicely formatted string.""" + # Otherwise the UTs fail because the order of the set can change + fields_str = ", ".join([str(e) for e in self.fields]) or "" + fields_str = " " + fields_str if fields_str else "" + return "([" + ", ".join(self.names) + "] -> " + (str(self.field_id) or "?") + fields_str + ")" + + +class NameMapping(IcebergRootModel[List[MappedField]]): + root: List[MappedField] + + @cached_property + def _field_by_id(self) -> Dict[int, MappedField]: + return visit_name_mapping(self, _IndexById()) + + @cached_property + def _field_by_name(self) -> Dict[str, MappedField]: + return visit_name_mapping(self, _IndexByName()) + + def id(self, name: str) -> int: + try: + return self._field_by_name[name].field_id + except KeyError as e: + raise ValueError(f"Could not find field with name: {name}") from e + + def field(self, field_id: int) -> MappedField: + try: + return self._field_by_id[field_id] + except KeyError as e: + raise ValueError(f"Could not find field-id: {field_id}") from e + + def __len__(self) -> int: + """Return the number of mappings.""" + return len(self.root) + + def __str__(self) -> str: + """Convert the name-mapping into a nicely formatted string.""" + if len(self.root) == 0: + return "[]" + else: + return "[\n " + "\n ".join([str(e) for e in self.root]) + "\n]" + + +T = TypeVar("T") + + +class NameMappingVisitor(Generic[T], ABC): + @abstractmethod + def mapping(self, nm: NameMapping, field_results: T) -> T: + """Visit a NameMapping.""" + + @abstractmethod + def fields(self, struct: List[MappedField], field_results: List[T]) -> T: + """Visit a List[MappedField].""" + + @abstractmethod + def field(self, field: MappedField, field_result: T) -> T: + """Visit a MappedField.""" + + +class _IndexById(NameMappingVisitor[Dict[int, MappedField]]): + result: Dict[int, MappedField] + + def __init__(self) -> None: + self.result = {} + + def mapping(self, nm: NameMapping, field_results: Dict[int, MappedField]) -> Dict[int, MappedField]: + return field_results + + def fields(self, struct: List[MappedField], field_results: List[Dict[int, MappedField]]) -> Dict[int, MappedField]: + return self.result + + def field(self, field: MappedField, field_result: Dict[int, MappedField]) -> Dict[int, MappedField]: + if field.field_id in self.result: + raise ValueError(f"Invalid mapping: ID {field.field_id} is not unique") + + self.result[field.field_id] = field + + return self.result + + +class _IndexByName(NameMappingVisitor[Dict[str, MappedField]]): + def mapping(self, nm: NameMapping, field_results: Dict[str, MappedField]) -> Dict[str, MappedField]: + return field_results + + def fields(self, struct: List[MappedField], field_results: List[Dict[str, MappedField]]) -> Dict[str, MappedField]: + return dict(ChainMap(*field_results)) + + def field(self, field: MappedField, field_result: Dict[str, MappedField]) -> Dict[str, MappedField]: + result: Dict[str, MappedField] = { + f"{field_name}.{key}": result_field for key, result_field in field_result.items() for field_name in field.names + } + + for name in field.names: + result[name] = field + + return result + + +@singledispatch +def visit_name_mapping(obj: Union[NameMapping, List[MappedField], MappedField], visitor: NameMappingVisitor[T]) -> T: + """Traverse the name mapping in post-order traversal.""" + raise NotImplementedError(f"Cannot visit non-type: {obj}") + + +@visit_name_mapping.register(NameMapping) +def _(obj: NameMapping, visitor: NameMappingVisitor[T]) -> T: + return visitor.mapping(obj, visit_name_mapping(obj.root, visitor)) + + +@visit_name_mapping.register(list) +def _(fields: List[MappedField], visitor: NameMappingVisitor[T]) -> T: + results = [visitor.field(field, visit_name_mapping(field.fields, visitor)) for field in fields] Review Comment: Yes, this is an interesting semantic discussion. When Pydantic deserializes, and it encounters that the `fields` field is missing, it will automatically inject an empty list: https://github.com/apache/iceberg-python/blob/623ad6ad2091583bc4ea0993912dbb830ea8d72e/pyiceberg/table/name_mapping.py#L40 When serializing to JSON, it will omit the `fields` key in the JSÓN object. This way we can just always assume that there is a list as it is annotated, and this is also why the type-checker isn't complaining. So it boils down to the definition: Is there a difference in meaning when `fields` is set to `None` or `[]`? -- This is an automated message from the Apache Git Service. To respond to the message, please log on to GitHub and use the URL above to go to the specific comment. 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