Add support for prefetching fields
This makes it possible to specify the fields that should be
prefetched as part of a getForFields query. Doing a prefetch on a
ReferenceProperty when it is known that the property will be
referenced in (almost all) entities is far more efficient than
doing the invididual fetches sequentially.
from django import forms
from django.contrib.gis.db.backend import SpatialBackend
from django.utils.translation import ugettext_lazy as _
class GeometryField(forms.Field):
"""
This is the basic form field for a Geometry. Any textual input that is
accepted by SpatialBackend.Geometry is accepted by this form. By default,
this is GEOSGeometry, which accepts WKT, HEXEWKB, WKB, and GeoJSON.
"""
widget = forms.Textarea
default_error_messages = {
'no_geom' : _(u'No geometry value provided.'),
'invalid_geom' : _(u'Invalid geometry value.'),
'invalid_geom_type' : _(u'Invalid geometry type.'),
}
def __init__(self, **kwargs):
self.null = kwargs.pop('null')
self.geom_type = kwargs.pop('geom_type')
super(GeometryField, self).__init__(**kwargs)
def clean(self, value):
"""
Validates that the input value can be converted to a Geometry
object (which is returned). A ValidationError is raised if
the value cannot be instantiated as a Geometry.
"""
if not value:
if self.null:
# The geometry column allows NULL, return None.
return None
else:
raise forms.ValidationError(self.error_messages['no_geom'])
try:
# Trying to create a Geometry object from the form value.
geom = SpatialBackend.Geometry(value)
except:
raise forms.ValidationError(self.error_messages['invalid_geom'])
# Ensuring that the geometry is of the correct type (indicated
# using the OGC string label).
if str(geom.geom_type).upper() != self.geom_type and not self.geom_type == 'GEOMETRY':
raise forms.ValidationError(self.error_messages['invalid_geom_type'])
return geom