from django.db.models.fields import Field,FieldDoesNotExist
from django.db.models.sql.constants import LOOKUP_SEP
from django.db.models.sql.expressions import SQLEvaluator
from django.db.models.sql.where import Constraint,WhereNode
from django.contrib.gis.db.models.fields import GeometryField
class GeoConstraint(Constraint):
"""
This subclass overrides `process` to better handle geographic SQL
construction.
"""
def __init__(self, init_constraint):
self.alias = init_constraint.alias
self.col = init_constraint.col
self.field = init_constraint.field
def process(self, lookup_type, value, connection):
if isinstance(value, SQLEvaluator):
# Make sure the F Expression destination field exists, and
# set an `srid` attribute with the same as that of the
# destination.
geo_fld = GeoWhereNode._check_geo_field(value.opts, value.expression.name)
if not geo_fld:
raise ValueError('No geographic field found in expression.')
value.srid = geo_fld.srid
db_type = self.field.db_type(connection=connection)
params = self.field.get_db_prep_lookup(lookup_type, value, connection=connection)
return (self.alias, self.col, db_type), params
class GeoWhereNode(WhereNode):
"""
Used to represent the SQL where-clause for spatial databases --
these are tied to the GeoQuery class that created it.
"""
def add(self, data, connector):
if isinstance(data, (list, tuple)):
obj, lookup_type, value = data
if ( isinstance(obj, Constraint) and
isinstance(obj.field, GeometryField) ):
data = (GeoConstraint(obj), lookup_type, value)
super(GeoWhereNode, self).add(data, connector)
def make_atom(self, child, qn, connection):
lvalue, lookup_type, value_annot, params_or_value = child
if isinstance(lvalue, GeoConstraint):
data, params = lvalue.process(lookup_type, params_or_value, connection)
spatial_sql = connection.ops.spatial_lookup_sql(data, lookup_type, params_or_value, lvalue.field, qn)
return spatial_sql, params
else:
return super(GeoWhereNode, self).make_atom(child, qn, connection)
@classmethod
def _check_geo_field(cls, opts, lookup):
"""
Utility for checking the given lookup with the given model options.
The lookup is a string either specifying the geographic field, e.g.
'point, 'the_geom', or a related lookup on a geographic field like
'address__point'.
If a GeometryField exists according to the given lookup on the model
options, it will be returned. Otherwise returns None.
"""
# This takes into account the situation where the lookup is a
# lookup to a related geographic field, e.g., 'address__point'.
field_list = lookup.split(LOOKUP_SEP)
# Reversing so list operates like a queue of related lookups,
# and popping the top lookup.
field_list.reverse()
fld_name = field_list.pop()
try:
geo_fld = opts.get_field(fld_name)
# If the field list is still around, then it means that the
# lookup was for a geometry field across a relationship --
# thus we keep on getting the related model options and the
# model field associated with the next field in the list
# until there's no more left.
while len(field_list):
opts = geo_fld.rel.to._meta
geo_fld = opts.get_field(field_list.pop())
except (FieldDoesNotExist, AttributeError):
return False
# Finally, make sure we got a Geographic field and return.
if isinstance(geo_fld, GeometryField):
return geo_fld
else:
return False
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