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from sqlalchemy import Table, MetaData |
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from sqlalchemy.engine import Engine |
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class CustomTable(Table): |
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def __getattr__(self, attr): |
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return getattr(self.c, attr) |
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def __bool__(self) -> None: |
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return self is not None |
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class LazyDBProp(object): |
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"""This descriptor returns sqlalchemy |
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Table class which can be used to query |
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table from the schema |
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""" |
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def __init__(self) -> None: |
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self._table = None |
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self._name = None |
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def __set_name__(self, _, name): |
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self._name = name |
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def __set__(self, instance, value): |
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if isinstance(value, (CustomTable, Table)): |
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self._table = value |
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def __get__(self, instance, _): |
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if self._table is None: |
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self._table = CustomTable( |
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self._name, instance.metadata, autoload=True) |
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return self._table |
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def get_lazy_class(engine: Engine) -> object: |
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""" |
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Function to create Lazy class for pulling table object |
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using SQLalchemy metadata |
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""" |
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def __init__(self, engine: Engine): |
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self.metadata = MetaData(engine) |
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self.engine = engine |
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def __getattr__(self, attr): |
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if attr not in self.__dict__: |
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obj = self.__patch(attr) |
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return obj.__get__(self, type(self)) |
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def __patch(self, attribute): |
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obj = LazyDBProp() |
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obj.__set_name__(self, attribute) |
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setattr(type(self), attribute, obj) |
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return obj |
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# naming classes uniquely for different schema's |
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# to avoid cross referencing |
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LazyClass = type(f"LazyClass_{engine.url.database}", (), {}) |
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LazyClass.__init__ = __init__ |
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LazyClass.__getattr__ = __getattr__ |
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LazyClass.__patch = __patch |
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return LazyClass(engine) |
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