FunctionElement is a class within the sqlalchemy.sql.functions module of the SQLAlchemy project.
GenericFunction
is another callable from the sqlalchemy.sql.functions package with code examples.
GeoAlchemy2 (project documentation and PyPI package information) extends SQLAlchemy with new data types for working with geospatial databases, particularly PostGIS, which is a spatial database extender for PostgreSQL. The project is provided as open source under the MIT license.
GeoAlchemy2 / geoalchemy2 / elements.py
# elements.py
import binascii
import struct
try:
from sqlalchemy.sql import functions
from sqlalchemy.sql.functions import FunctionElement
except ImportError: # SQLA < 0.9 # pragma: no cover
from sqlalchemy.sql import expression as functions
from sqlalchemy.sql.expression import FunctionElement
from sqlalchemy.types import to_instance
from sqlalchemy.ext.compiler import compiles
from .compat import PY3, str as str_
from .exc import ArgumentError
if PY3:
BinasciiError = binascii.Error
else:
BinasciiError = TypeError
class HasFunction(object):
pass
class _SpatialElement(HasFunction):
def __init__(self, data, srid=-1, extended=False):
self.srid = srid
## ... source file abbreviated to get to FunctionElement examples ...
geom_from_extended_version = 'raster'
def __init__(self, data):
try:
bin_data = binascii.unhexlify(data[:114])
except BinasciiError:
bin_data = data
data = str(binascii.hexlify(data).decode(encoding='utf-8'))
byte_order = bin_data[0]
srid = bin_data[53:57]
if not PY3:
byte_order = bytearray(byte_order)[0]
srid = struct.unpack('<I' if byte_order else '>I', srid)[0]
_SpatialElement.__init__(self, data, srid, True)
@property
def desc(self):
return self.data
@staticmethod
def _data_from_desc(desc):
return desc
class CompositeElement(FunctionElement):
def __init__(self, base, field, type_):
self.name = field
self.type = to_instance(type_)
super(CompositeElement, self).__init__(base)
@compiles(CompositeElement)
def _compile_pgelem(expr, compiler, **kw):
return '(%s).%s' % (compiler.process(expr.clauses, **kw), expr.name)
## ... source file continues with no further FunctionElement examples...