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import abc |
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from typing import Any, Optional |
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from etlt.writer.Writer import Writer |
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class SqlLoaderWriter(Writer): |
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""" |
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Abstract parent class for loading rows to a table in a database using a SQL statement for loading data from file. |
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""" |
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handlers = {} |
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""" |
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The handlers for writing objects as a field to a CSV file. |
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:type: dict[str,callable] |
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""" |
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# ------------------------------------------------------------------------------------------------------------------ |
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def __init__(self, filename: str, encoding: str = 'utf8'): |
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""" |
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Object constructor. |
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:param filename: The destination file for the rows. |
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:param encoding: The encoding of the text of the destination file. |
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""" |
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Writer.__init__(self) |
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self._filename: str = filename |
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""" |
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The name of the destination file. |
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""" |
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self._encoding: str = encoding |
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""" |
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The encoding of the text in the destination file. |
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""" |
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self._file: Any = None |
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""" |
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The underling file object. |
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""" |
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# ------------------------------------------------------------------------------------------------------------------ |
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def __enter__(self): |
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self._file = open(self._filename, mode='wt', encoding=self._encoding) |
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# ------------------------------------------------------------------------------------------------------------------ |
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def __exit__(self, exc_type, exc_value, traceback): |
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self._file.close() |
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# ------------------------------------------------------------------------------------------------------------------ |
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@property |
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def filename(self) -> str: |
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""" |
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Returns the filename. |
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""" |
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return self._filename |
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# ------------------------------------------------------------------------------------------------------------------ |
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@property |
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def encoding(self) -> str: |
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""" |
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Returns the encoding. |
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""" |
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return self._encoding |
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# ------------------------------------------------------------------------------------------------------------------ |
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@abc.abstractmethod |
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def get_bulk_load_sql(self, table_name: str, partition: Optional[str] = None) -> str: |
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""" |
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Returns a SQL statement for bulk loading the data writen to the destination file into a table. |
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:param table_name: The name of the table. |
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:param partition: When applicable, the name of the partition in which the data must be loaded.` |
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""" |
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raise NotImplementedError() |
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# ------------------------------------------------------------------------------------------------------------------ |
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@staticmethod |
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def register_handler(class_name: str, handler: callable) -> None: |
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""" |
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Registers a handler for writing instances of a class as a field to the destination file. |
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:param class_name: The name of the class. |
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:param handler: The handler. This handler will be called with two arguments: the object which value must be |
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writen to the destination file, the file handler. |
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""" |
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SqlLoaderWriter.handlers[class_name] = handler |
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# ------------------------------------------------------------------------------------------------------------------ |
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def _write_field(self, value: Any): |
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""" |
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Writes a single field to the destination file. |
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:param value: The value of the field. |
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""" |
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class_name = str(value.__class__) |
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if class_name not in self.handlers: |
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raise ValueError('No handler has been registered for class: {0!s}'.format(class_name)) |
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handler = self.handlers[class_name] |
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handler(value, self._file) |
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# ---------------------------------------------------------------------------------------------------------------------- |
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PyETLT /
etlt
