Source code for geoalchemy2.comparator

"""

This module defines a ``Comparator`` class for use with geometry and geography
objects. This is where spatial operators, like ``&&``, ``&<``, are defined.
Spatial operators very often apply to the bounding boxes of geometries. For
example, ``geom1 && geom2`` indicates if geom1's bounding box intersects
geom2's.

Examples
--------

Select the objects whose bounding boxes are to the left of the
bounding box of ``POLYGON((-5 45,5 45,5 -45,-5 -45,-5 45))``::

    select([table]).where(table.c.geom.to_left(
        'POLYGON((-5 45,5 45,5 -45,-5 -45,-5 45))'))

The ``<<`` and ``>>`` operators are a bit specific, because they have
corresponding Python operator (``__lshift__`` and ``__rshift__``). The
above ``SELECT`` expression can thus be rewritten like this::

    select([table]).where(
        table.c.geom << 'POLYGON((-5 45,5 45,5 -45,-5 -45,-5 45))')

Operators can also be used when using the ORM. For example::

    Session.query(Cls).filter(
        Cls.geom << 'POLYGON((-5 45,5 45,5 -45,-5 -45,-5 45))')

Now some other examples with the ``<#>`` operator.

Select the ten objects that are the closest to ``POINT(0 0)`` (typical
closed neighbors problem)::

    select([table]).order_by(table.c.geom.distance_box('POINT(0 0)')).limit(10)

Using the ORM::

    Session.query(Cls).order_by(Cls.geom.distance_box('POINT(0 0)')).limit(10)

Reference
---------
"""

from sqlalchemy import types as sqltypes
from sqlalchemy.types import UserDefinedType
from sqlalchemy.dialects.postgresql import DOUBLE_PRECISION
from sqlalchemy.sql import operators
try:
    from sqlalchemy.sql.functions import _FunctionGenerator
except ImportError:  # SQLA < 0.9  # pragma: no cover
    from sqlalchemy.sql.expression import _FunctionGenerator


INTERSECTS = operators.custom_op('&&')
OVERLAPS_OR_TO_LEFT = operators.custom_op('&<')
OVERLAPS_OR_TO_RIGHT = operators.custom_op('&>')
OVERLAPS_OR_BELOW = operators.custom_op('&<|')
TO_LEFT = operators.custom_op('<<')
BELOW = operators.custom_op('<<|')
TO_RIGHT = operators.custom_op('>>')
CONTAINED = operators.custom_op('@')
OVERLAPS_OR_ABOVE = operators.custom_op('|&>')
ABOVE = operators.custom_op('|>>')
CONTAINS = operators.custom_op('~')
SAME = operators.custom_op('~=')
DISTANCE_CENTROID = operators.custom_op('<->')
DISTANCE_BOX = operators.custom_op('<#>')


[docs]class BaseComparator(UserDefinedType.Comparator): """ A custom comparator base class. It adds the ability to call spatial functions on columns that use this kind of comparator. It also defines functions that map to operators supported by ``Geometry``, ``Geography`` and ``Raster`` columns. This comparator is used by the :class:`geoalchemy2.types.Raster`. """ key = None def __getattr__(self, name): # Function names that don't start with "ST_" are rejected. # This is not to mess up with SQLAlchemy's use of # hasattr/getattr on Column objects. if not name.lower().startswith('st_'): raise AttributeError # We create our own _FunctionGenerator here, and use it in place of # SQLAlchemy's "func" object. This is to be able to "bind" the # function to the SQL expression. See also GenericFunction. func_ = _FunctionGenerator(expr=self.expr) return getattr(func_, name)
[docs] def intersects(self, other): """ The ``&&`` operator. A's BBOX intersects B's. """ return self.operate(INTERSECTS, other, result_type=sqltypes.Boolean)
[docs] def overlaps_or_to_left(self, other): """ The ``&<`` operator. A's BBOX overlaps or is to the left of B's. """ return self.operate(OVERLAPS_OR_TO_LEFT, other, result_type=sqltypes.Boolean)
[docs] def overlaps_or_to_right(self, other): """ The ``&>`` operator. A's BBOX overlaps or is to the right of B's. """ return self.operate(OVERLAPS_OR_TO_RIGHT, other, result_type=sqltypes.Boolean)
[docs]class Comparator(BaseComparator): """ A custom comparator class. Used in :class:`geoalchemy2.types.Geometry` and :class:`geoalchemy2.types.Geography`. This is where spatial operators like ``<<`` and ``<->`` are defined. """
[docs] def overlaps_or_below(self, other): """ The ``&<|`` operator. A's BBOX overlaps or is below B's. """ return self.operate(OVERLAPS_OR_BELOW, other, result_type=sqltypes.Boolean)
[docs] def to_left(self, other): """ The ``<<`` operator. A's BBOX is strictly to the left of B's. """ return self.operate(TO_LEFT, other, result_type=sqltypes.Boolean)
[docs] def __lshift__(self, other): """ The ``<<`` operator. A's BBOX is strictly to the left of B's. Same as ``to_left``, so:: table.c.geom << 'POINT(1 2)' is the same as:: table.c.geom.to_left('POINT(1 2)') """ return self.to_left(other)
[docs] def below(self, other): """ The ``<<|`` operator. A's BBOX is strictly below B's. """ return self.operate(BELOW, other, result_type=sqltypes.Boolean)
[docs] def to_right(self, other): """ The ``>>`` operator. A's BBOX is strictly to the right of B's. """ return self.operate(TO_RIGHT, other, result_type=sqltypes.Boolean)
[docs] def __rshift__(self, other): """ The ``>>`` operator. A's BBOX is strictly to the left of B's. Same as `to_`right``, so:: table.c.geom >> 'POINT(1 2)' is the same as:: table.c.geom.to_right('POINT(1 2)') """ return self.to_right(other)
[docs] def contained(self, other): """ The ``@`` operator. A's BBOX is contained by B's. """ return self.operate(CONTAINED, other, result_type=sqltypes.Boolean)
[docs] def overlaps_or_above(self, other): """ The ``|&>`` operator. A's BBOX overlaps or is above B's. """ return self.operate(OVERLAPS_OR_ABOVE, other, result_type=sqltypes.Boolean)
[docs] def above(self, other): """ The ``|>>`` operator. A's BBOX is strictly above B's. """ return self.operate(ABOVE, other, result_type=sqltypes.Boolean)
[docs] def contains(self, other, **kw): """ The ``~`` operator. A's BBOX contains B's. """ return self.operate(CONTAINS, other, result_type=sqltypes.Boolean)
[docs] def same(self, other): """ The ``~=`` operator. A's BBOX is the same as B's. """ return self.operate(SAME, other, result_type=sqltypes.Boolean)
[docs] def distance_centroid(self, other): """ The ``<->`` operator. The distance between two points. """ return self.operate(DISTANCE_CENTROID, other, result_type=DOUBLE_PRECISION)
[docs] def distance_box(self, other): """ The ``<#>`` operator. The distance between bounding box of two geometries. """ return self.operate(DISTANCE_BOX, other, result_type=DOUBLE_PRECISION)