1 from django.db.models.sql.aggregates import *

     2 from django.contrib.gis.db.models.fields import GeometryField

     3 from django.contrib.gis.db.models.sql.conversion import GeomField

     4 

     5 class GeoAggregate(Aggregate):

     6     # Default SQL template for spatial aggregates.

     7     sql_template = '%(function)s(%(field)s)'

     8 

     9     # Conversion class, if necessary.

    10     conversion_class = None

    11 

    12     # Flags for indicating the type of the aggregate.

    13     is_extent = False

    14 

    15     def __init__(self, col, source=None, is_summary=False, tolerance=0.05, **extra):

    16         super(GeoAggregate, self).__init__(col, source, is_summary, **extra)

    17 

    18         # Required by some Oracle aggregates.

    19         self.tolerance = tolerance

    20 

    21         # Can't use geographic aggregates on non-geometry fields.

    22         if not isinstance(self.source, GeometryField):

    23             raise ValueError('Geospatial aggregates only allowed on geometry fields.')

    24 

    25     def as_sql(self, qn, connection):

    26         "Return the aggregate, rendered as SQL."

    27 

    28         if connection.ops.oracle:

    29             self.extra['tolerance'] = self.tolerance

    30 

    31         if hasattr(self.col, 'as_sql'):

    32             field_name = self.col.as_sql(qn, connection)

    33         elif isinstance(self.col, (list, tuple)):

    34             field_name = '.'.join([qn(c) for c in self.col])

    35         else:

    36             field_name = self.col

    37 

    38         sql_template, sql_function = connection.ops.spatial_aggregate_sql(self)

    39 

    40         params = {

    41             'function': sql_function,

    42             'field': field_name

    43         }

    44         params.update(self.extra)

    45 

    46         return sql_template % params

    47 

    48 class Collect(GeoAggregate):

    49     pass

    50 

    51 class Extent(GeoAggregate):

    52     is_extent = '2D'

    53 

    54 class Extent3D(GeoAggregate):

    55     is_extent = '3D'

    56 

    57 class MakeLine(GeoAggregate):

    58     pass

    59 

    60 class Union(GeoAggregate):

    61     pass