paimon-python/pypaimon/read/reader/format_pyarrow_reader.py

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from typing import Any, List, Optional

import pyarrow as pa
import pyarrow.dataset as ds
from pyarrow import RecordBatch

from pypaimon.common.file_io import FileIO
from pypaimon.read.reader.iface.record_batch_reader import RecordBatchReader


class FormatPyArrowReader(RecordBatchReader):
    """
    A Format Reader that reads record batch from a Parquet or ORC file using PyArrow,
    and filters it based on the provided predicate and projection.
    """

    def __init__(self, file_io: FileIO, file_format: str, file_path: str, read_fields: List[str],
                 push_down_predicate: Any, batch_size: int = 4096):
        file_path_for_pyarrow = file_io.to_filesystem_path(file_path)
        self.dataset = ds.dataset(file_path_for_pyarrow, format=file_format, filesystem=file_io.filesystem)
        self.read_fields = read_fields

        # Identify which fields exist in the file and which are missing
        file_schema_names = set(self.dataset.schema.names)
        self.existing_fields = [field for field in read_fields if field in file_schema_names]
        self.missing_fields = [field for field in read_fields if field not in file_schema_names]

        # Only pass existing fields to PyArrow scanner to avoid errors
        self.reader = self.dataset.scanner(
            columns=self.existing_fields,
            filter=push_down_predicate,
            batch_size=batch_size
        ).to_reader()

    def read_arrow_batch(self) -> Optional[RecordBatch]:
        try:
            batch = self.reader.read_next_batch()

            if not self.missing_fields:
                return batch

            # Create columns for missing fields with null values
            missing_columns = [pa.nulls(batch.num_rows, type=pa.null()) for _ in self.missing_fields]

            # Reconstruct the batch with all fields in the correct order
            all_columns = []
            for field_name in self.read_fields:
                if field_name in self.existing_fields:
                    # Get the column from the existing batch
                    column_idx = self.existing_fields.index(field_name)
                    all_columns.append(batch.column(column_idx))
                else:
                    # Get the column from missing fields
                    column_idx = self.missing_fields.index(field_name)
                    all_columns.append(missing_columns[column_idx])

            # Create a new RecordBatch with all columns
            return pa.RecordBatch.from_arrays(all_columns, names=self.read_fields)

        except StopIteration:
            return None

    def close(self):
        if self.reader is not None:
            self.reader = None