geography.py

# Copyright (c) 2021 The PyBigQuery Authors
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import geoalchemy2
from geoalchemy2.shape import to_shape
import geoalchemy2.functions
from shapely import wkb, wkt
import sqlalchemy.ext.compiler
from sqlalchemy.sql.elements import BindParameter

SRID = 4326  # WGS84, https://spatialreference.org/ref/epsg/wgs-84/


class WKB(geoalchemy2.WKBElement):
    """
    Well-Known-Binary data wrapper.

    WKB objects hold geographic data in a binary format known as
    "Well-Known Binary",
    <https://en.wikipedia.org/wiki/Well-known_text_representation_of_geometry>.
    These objects are returned from queries and can be used in insert
    and queries.

    The WKB class is a subclass of the Geoalchemy2 WKBElement class
    customized for working with BigQuery.
    """

    geom_from_extended_version = "ST_GeogFromWKB"

    def __init__(self, data):
        super().__init__(data, SRID, True)

    @property
    def wkt(self):
        """
        Return the WKB object as a WKT object.
        """
        return WKT(to_shape(self).wkt)


class WKT(geoalchemy2.WKTElement):
    """
    Well-Known-Text data wrapper.

    WKT objects hold geographic data in a text format known as
    "Well-Known Text",
    <https://en.wikipedia.org/wiki/Well-known_text_representation_of_geometry>.

    You generally shouldn't need to create WKT objects directly, as
    text arguments to geographic functions and inserts to GEOGRAPHY
    columns are automatically coerced to geographic data.

    The WKT class is a subclass of the Geoalchemy2 WKTElement class
    customized for working with BigQuery.
    """

    geom_from_extended_version = "ST_GeogFromText"

    def __init__(self, data):
        super().__init__(data, SRID, True)

    @property
    def wkb(self):
        """
        Return the WKT object as a WKB object.
        """
        return WKB(wkb.dumps(wkt.loads(self.data)))


class GEOGRAPHY(geoalchemy2.Geography):
    """
    GEOGRAPHY type

    Use this to define BigQuery GEOGRAPHY columns::

        class Lake(Base):
            __tablename__ = 'lakes'

            name = Column(String)
            geog = column(GEOGRAPHY)

    See https://googleapis.dev/python/sqlalchemy-bigquery/latest/geography.html
    """

    def __init__(self):
        super().__init__(
            geometry_type=None,
            spatial_index=False,
            srid=SRID,
        )
        self.extended = True

    # Un-inherit the bind function that adds an ST_GeogFromText.
    # It's unnecessary and causes BigQuery to error.
    #
    # Some things to note about this:
    #
    # 1. bind_expression can't always know the value.  When multiple
    #    rows are being inserted, the values may be different in each
    #    row.  As a consequence, we have to treat all the values as WKT.
    #
    # 2. This applies equally to explicitly converting with
    #    st_geogfromtext, or implicitly with the geography parameter
    #    conversion.
    #
    # 3. We handle different types using bind_processor, below.
    #
    bind_expression = sqlalchemy.sql.type_api.TypeEngine.bind_expression

    def bind_processor(self, dialect):
        """
        SqlAlchemy plugin that controls how values are converted to parameters

        When we bind values, we always bind as text.  We have to do
        this because when we decide how to bind, we don't always know
        what the values will be.

        This is not a user-facing method.
        """

        def process(bindvalue):
            if isinstance(bindvalue, WKT):
                return bindvalue.data
            elif isinstance(bindvalue, WKB):
                return bindvalue.wkt.data
            else:
                return bindvalue

        return process

    @staticmethod
    def ElementType(data, srid=SRID, extended=True):
        """
        Plugin for the Geoalchemy2 framework for constructing WKB objects.

        The framework wants a callable, which it assumes is a class
        (this the name), for constructing a geographic element.

        We don't want `WKB` to accept extra arguments that it checks
        and ignores, so we do that in this wrapper.

        This is not a user-facing method.
        """
        if srid != SRID:
            raise AssertionError("Bad srid", srid)
        if not extended:
            raise AssertionError("Extended must be True.")
        return WKB(data)


@sqlalchemy.ext.compiler.compiles(geoalchemy2.functions.GenericFunction, "bigquery")
def _fixup_st_arguments(element, compiler, **kw):
    """
    Compiler-plugin for the BigQuery that overrides how geographic functions are handled

    Geographic function (ST_...) get turned into
    `geoalchemy2.functions.GenericFunction` objects by
    Geoalchemy2. The code here overrides how they're handeled.

    We want arguments passed to have the GEOGRAPHY type associated
    with them, when appropriate, where "when appropriate" is
    determined by the `function documentation
    <https://cloud.google.com/bigquery/docs/reference/standard-sql/geography_functions>`_..

    This is not a user-facing function.
    """
    argument_types = _argument_types.get(element.name.lower())
    if argument_types:
        for argument_type, argument in zip(argument_types, element.clauses.clauses):
            if isinstance(argument, BindParameter) and (
                argument.type is not argument_type
                or not isinstance(argument.type, argument_type)
            ):
                argument.type = argument_type()

    return compiler.visit_function(element, **kw)


_argument_types = dict(
    st_area=(GEOGRAPHY,),
    st_asbinary=(GEOGRAPHY,),
    st_asgeojson=(GEOGRAPHY,),
    st_astext=(GEOGRAPHY,),
    st_boundary=(GEOGRAPHY,),
    st_centroid=(GEOGRAPHY,),
    st_centroid_agg=(GEOGRAPHY,),
    st_closestpoint=(
        GEOGRAPHY,
        GEOGRAPHY,
    ),
    st_clusterdbscan=(GEOGRAPHY,),
    st_contains=(
        GEOGRAPHY,
        GEOGRAPHY,
    ),
    st_convexhull=(GEOGRAPHY,),
    st_coveredby=(
        GEOGRAPHY,
        GEOGRAPHY,
    ),
    st_covers=(
        GEOGRAPHY,
        GEOGRAPHY,
    ),
    st_difference=(
        GEOGRAPHY,
        GEOGRAPHY,
    ),
    st_dimension=(GEOGRAPHY,),
    st_disjoint=(
        GEOGRAPHY,
        GEOGRAPHY,
    ),
    st_distance=(
        GEOGRAPHY,
        GEOGRAPHY,
    ),
    st_dump=(GEOGRAPHY,),
    st_dwithin=(
        GEOGRAPHY,
        GEOGRAPHY,
    ),
    st_endpoint=(GEOGRAPHY,),
    st_equals=(
        GEOGRAPHY,
        GEOGRAPHY,
    ),
    st_exteriorring=(GEOGRAPHY,),
    st_geohash=(GEOGRAPHY,),
    st_intersection=(
        GEOGRAPHY,
        GEOGRAPHY,
    ),
    st_intersects=(
        GEOGRAPHY,
        GEOGRAPHY,
    ),
    st_intersectsbox=(GEOGRAPHY,),
    st_iscollection=(GEOGRAPHY,),
    st_isempty=(GEOGRAPHY,),
    st_length=(GEOGRAPHY,),
    st_makeline=(
        GEOGRAPHY,
        GEOGRAPHY,
    ),
    st_makepolygon=(
        GEOGRAPHY,
        GEOGRAPHY,
    ),
    st_makepolygonoriented=(GEOGRAPHY,),
    st_maxdistance=(
        GEOGRAPHY,
        GEOGRAPHY,
    ),
    st_npoints=(GEOGRAPHY,),
    st_numpoints=(GEOGRAPHY,),
    st_perimeter=(GEOGRAPHY,),
    st_pointn=(GEOGRAPHY,),
    st_simplify=(GEOGRAPHY,),
    st_snaptogrid=(GEOGRAPHY,),
    st_startpoint=(GEOGRAPHY,),
    st_touches=(
        GEOGRAPHY,
        GEOGRAPHY,
    ),
    st_union=(
        GEOGRAPHY,
        GEOGRAPHY,
    ),
    st_union_agg=(GEOGRAPHY,),
    st_within=(
        GEOGRAPHY,
        GEOGRAPHY,
    ),
    st_x=(GEOGRAPHY,),
    st_y=(GEOGRAPHY,),
)

__all__ = ["GEOGRAPHY", "WKB", "WKT"]