49 lines
1.5 KiB
Python
49 lines
1.5 KiB
Python
|
"""Provide the ORM's `Grid` model."""
|
||
|
|
|
||
|
|
import sqlalchemy as sa
|
||
|
|
from sqlalchemy import orm
|
||
|
|
|
||
|
|
from urban_meal_delivery.db import meta
|
||
|
|
|
||
|
|
|
||
|
|
class Grid(meta.Base):
|
||
|
|
"""A grid of `Pixel`s to partition a `City`.
|
||
|
|
|
||
|
|
A grid is characterized by the uniform size of the `Pixel`s it contains.
|
||
|
|
That is configures via the `Grid.side_length` attribute.
|
||
|
|
"""
|
||
|
|
|
||
|
|
__tablename__ = 'grids'
|
||
|
|
|
||
|
|
# Columns
|
||
|
|
id = sa.Column( # noqa:WPS125
|
||
|
|
sa.SmallInteger, primary_key=True, autoincrement=True,
|
||
|
|
)
|
||
|
|
_city_id = sa.Column('city_id', sa.SmallInteger, nullable=False)
|
||
|
|
side_length = sa.Column(sa.SmallInteger, nullable=False, unique=True)
|
||
|
|
|
||
|
|
# Constraints
|
||
|
|
__table_args__ = (
|
||
|
|
sa.ForeignKeyConstraint(
|
||
|
|
['city_id'], ['cities.id'], onupdate='RESTRICT', ondelete='RESTRICT',
|
||
|
|
),
|
||
|
|
# Needed by a `ForeignKeyConstraint` in `address_pixel_association`.
|
||
|
|
sa.UniqueConstraint('id', 'city_id'),
|
||
|
|
)
|
||
|
|
|
||
|
|
# Relationships
|
||
|
|
city = orm.relationship('City', back_populates='grids')
|
||
|
|
pixels = orm.relationship('Pixel', back_populates='grid')
|
||
|
|
|
||
|
|
def __repr__(self) -> str:
|
||
|
|
"""Non-literal text representation."""
|
||
|
|
return '<{cls}: {area}>'.format(
|
||
|
|
cls=self.__class__.__name__, area=self.pixel_area,
|
||
|
|
)
|
||
|
|
|
||
|
|
# Convenience properties
|
||
|
|
@property
|
||
|
|
def pixel_area(self) -> float:
|
||
|
|
"""The area of a `Pixel` on the grid in square kilometers."""
|
||
|
|
return (self.side_length ** 2) / 1_000_000 # noqa:WPS432
|