gis: Added the extent method to GeoQuerySet; moved various spatial-backend settings into the SpatialBackend container class.

git-svn-id: http://code.djangoproject.com/svn/django/branches/gis@7028 bcc190cf-cafb-0310-a4f2-bffc1f526a37

django/contrib/gis/db/backend/__init__.py

@@ -5,17 +5,14 @@
  needed for GeoDjango.
  
  (1) GeoBackEndField, a base class needed for GeometryField.
- (2) GeometryProxy, for lazy-instantiated geometries from the 
+ (2) GIS_TERMS, a list of acceptable geographic lookup types for 
-     database output.
- (3) GIS_TERMS, a list of acceptable geographic lookup types for 
      the backend.
- (4) The `parse_lookup` function, used for spatial SQL construction by
+ (3) The `parse_lookup` function, used for spatial SQL construction by
      the GeoQuerySet.
- (5) The `create_spatial_db`, and `get_geo_where_clause`
+ (4) The `create_spatial_db`, and `get_geo_where_clause`
      routines (needed by `parse_lookup`).
-
+ (5) The `SpatialBackend` object, which contains information specific
- Currently only PostGIS is supported, but someday backends will be added for
+     to the spatial backend.
- additional spatial databases (e.g., Oracle, DB2).
 """
 from types import StringType, UnicodeType
 from django.conf import settings
@@ -26,7 +23,7 @@ from django.utils.datastructures import SortedDict
 from django.contrib.gis.geos import GEOSGeometry
 
 # These routines (needed by GeoManager), default to False.
-ASGML, ASKML, DISTANCE, TRANSFORM, UNION, VERSION = (False, False, False, False, False, False)
+ASGML, ASKML, DISTANCE, EXTENT, TRANSFORM, UNION, VERSION = (False, False, False, False, False, False, False)
 
 if settings.DATABASE_ENGINE == 'postgresql_psycopg2':
     # PostGIS is the spatial database, getting the rquired modules, 
@@ -34,7 +31,7 @@ if settings.DATABASE_ENGINE == 'postgresql_psycopg2':
     from django.contrib.gis.db.backend.postgis import \
         PostGISField as GeoBackendField, POSTGIS_TERMS as GIS_TERMS, \
         create_spatial_db, get_geo_where_clause, \
-        ASGML, ASKML, DISTANCE, GEOM_SELECT, TRANSFORM, UNION, \
+        ASGML, ASKML, DISTANCE, EXTENT, GEOM_SELECT, TRANSFORM, UNION, \
         MAJOR_VERSION, MINOR_VERSION1, MINOR_VERSION2
     VERSION = (MAJOR_VERSION, MINOR_VERSION1, MINOR_VERSION2)
     SPATIAL_BACKEND = 'postgis'
@@ -55,6 +52,18 @@ elif settings.DATABASE_ENGINE == 'mysql':
 else:
     raise NotImplementedError('No Geographic Backend exists for %s' % settings.DATABASE_ENGINE)
 
+class SpatialBackend(object):
+    "A container for properties of the Spatial Backend."
+    as_kml = ASKML
+    as_gml = ASGML
+    distance = DISTANCE
+    extent = EXTENT
+    name = SPATIAL_BACKEND
+    select = GEOM_SELECT
+    transform = TRANSFORM
+    union = UNION
+    version = VERSION
+
 ####    query.py overloaded functions    ####
 # parse_lookup() and lookup_inner() are modified from their django/db/models/query.py
 #  counterparts to support constructing SQL for geographic queries.

django/contrib/gis/db/backend/postgis/__init__.py

@@ -6,4 +6,4 @@ from django.contrib.gis.db.backend.postgis.field import PostGISField, gqn
 from django.contrib.gis.db.backend.postgis.query import \
     get_geo_where_clause, GEOM_FUNC_PREFIX, POSTGIS_TERMS, \
     MAJOR_VERSION, MINOR_VERSION1, MINOR_VERSION2, \
-    ASKML, ASGML, DISTANCE, GEOM_FROM_TEXT, UNION, TRANSFORM, GEOM_SELECT
+    ASKML, ASGML, DISTANCE, EXTENT, GEOM_FROM_TEXT, UNION, TRANSFORM, GEOM_SELECT

django/contrib/gis/db/backend/postgis/query.py

@@ -40,6 +40,7 @@ if MAJOR_VERSION >= 1:
     ASKML = get_func('AsKML')
     ASGML = get_func('AsGML')
     DISTANCE = get_func('Distance')
+    EXTENT = get_func('extent')
     GEOM_FROM_TEXT = get_func('GeomFromText')
     GEOM_FROM_WKB = get_func('GeomFromWKB')
     TRANSFORM = get_func('Transform')

django/contrib/gis/db/models/manager.py

@@ -10,6 +10,9 @@ class GeoManager(Manager):
     def distance(self, *args, **kwargs):
         return self.get_query_set().distance(*args, **kwargs)
 
+    def extent(self, *args, **kwargs):
+        return self.get_query_set().extent(*args, **kwargs)
+
     def gml(self, *args, **kwargs):
         return self.get_query_set().gml(*args, **kwargs)
 

django/contrib/gis/db/models/query.py

@@ -6,13 +6,12 @@ from django.db.models.fields import FieldDoesNotExist
 from django.utils.datastructures import SortedDict
 from django.contrib.gis.db.models.fields import GeometryField
 # parse_lookup depends on the spatial database backend.
-from django.contrib.gis.db.backend import parse_lookup, \
+from django.contrib.gis.db.backend import parse_lookup, SpatialBackend
-    ASGML, ASKML, DISTANCE, GEOM_SELECT, SPATIAL_BACKEND, TRANSFORM, UNION, VERSION
 from django.contrib.gis.geos import GEOSGeometry
 
 # Shortcut booleans for determining the backend.
-oracle = SPATIAL_BACKEND == 'oracle'
+oracle  = SpatialBackend.name == 'oracle'
-postgis = SPATIAL_BACKEND == 'postgis'
+postgis = SpatialBackend.name == 'postgis'
 
 class GeoQ(Q):
     "Geographical query encapsulation object."
@@ -23,7 +22,7 @@ class GeoQ(Q):
 
 class GeoQuerySet(QuerySet):
     "Geographical-enabled QuerySet object."
-    
+        
     #### Overloaded QuerySet Routines ####
     def __init__(self, model=None):
         super(GeoQuerySet, self).__init__(model=model)
@@ -37,10 +36,10 @@ class GeoQuerySet(QuerySet):
 
         # If GEOM_SELECT is defined in the backend, then it will be used
         # for the selection format of the geometry column.
-        if GEOM_SELECT:
+        if SpatialBackend.select:
             # Transformed geometries in Oracle use EWKT so that the SRID
             # on the transformed lazy geometries is set correctly).
-            self._geo_fmt = GEOM_SELECT
+            self._geo_fmt = SpatialBackend.select
         else:
             self._geo_fmt = '%s'
 
@@ -259,6 +258,7 @@ class GeoQuerySet(QuerySet):
         given geometry in a `distance` attribute on each element of the
         GeoQuerySet.
         """
+        DISTANCE = SpatialBackend.distance
         if not DISTANCE:
             raise ImproperlyConfigured('Distance() stored proecedure not available.')
 
@@ -299,12 +299,55 @@ class GeoQuerySet(QuerySet):
             dist_select = {'distance' : '%s(%s, %s)' % (DISTANCE, field_col, geom_sql)}
         return self.extra(select=dist_select)
 
+    def extent(self, field_name=None):
+        """
+        Returns the extent (aggregate) of the features in the GeoQuerySet.  The
+        extent will be returned as a 4-tuple, consisting of (xmin, ymin, xmax, ymax).
+        """
+        EXTENT = SpatialBackend.extent
+        if not EXTENT:
+            raise ImproperlyConfigured('Extent stored procedure not available.')
+
+        if not field_name:
+            field_name = self._get_geofield()
+
+        field_col = self._geo_column(field_name)
+        if not field_col:
+            raise TypeError('Extent information only available on GeometryFields.')
+
+        # Getting the SQL for the query.
+        try:
+            select, sql, params = self._get_sql_clause()
+        except EmptyResultSet:
+            return None
+        
+        # Constructing the query that will select the extent.
+        extent_sql = ('SELECT %s(%s)' % (EXTENT, field_col)) + sql
+
+        # Getting a cursor, executing the query, and extracting the returned
+        # value from the extent function.
+        cursor = connection.cursor()
+        cursor.execute(extent_sql, params)
+        box = cursor.fetchone()[0]
+
+        if box: 
+            # TODO: Parsing of BOX3D, Oracle support (patches welcome!)
+            #  Box text will be something like "BOX(-90.0 30.0, -85.0 40.0)"; 
+            #  parsing out and returning as a 4-tuple.
+            ll, ur = box[4:-1].split(',')
+            xmin, ymin = map(float, ll.split())
+            xmax, ymax = map(float, ur.split())
+            return (xmin, ymin, xmax, ymax)
+        else: 
+            return None
+
     def gml(self, field_name=None, precision=8, version=2):
         """
         Returns GML representation of the given field in a `gml` attribute
         on each element of the GeoQuerySet.
         """
         # Is GML output supported?
+        ASGML = SpatialBackend.as_gml
         if not ASGML:
             raise ImproperlyConfigured('AsGML() stored procedure not available.')
 
@@ -322,7 +365,7 @@ class GeoQuerySet(QuerySet):
         elif postgis:
             # PostGIS AsGML() aggregate function parameter order depends on the
             # version -- uggh.
-            major, minor1, minor2 = VERSION
+            major, minor1, minor2 = SpatialBackend.version
             if major >= 1 and (minor1 > 3 or (minor1 == 3 and minor2 > 1)):
                 gml_select = {'gml':'%s(%s,%s,%s)' % (ASGML, version, field_col, precision)}
             else:
@@ -337,6 +380,7 @@ class GeoQuerySet(QuerySet):
         attribute on each element of the GeoQuerySet.
         """
         # Is KML output supported?
+        ASKML = SpatialBackend.as_kml
         if not ASKML:
             raise ImproperlyConfigured('AsKML() stored procedure not available.')
 
@@ -375,6 +419,7 @@ class GeoQuerySet(QuerySet):
 
         # Setting the key for the field's column with the custom SELECT SQL to 
         # override the geometry column returned from the database.
+        TRANSFORM = SpatialBackend.transform
         if oracle:
             custom_sel = '%s(%s, %s)' % (TRANSFORM, col, srid)
             self._ewkt = srid
@@ -391,6 +436,7 @@ class GeoQuerySet(QuerySet):
         Oracle backends only.
         """
         # Making sure backend supports the Union stored procedure
+        UNION = SpatialBackend.union
         if not UNION:
             raise ImproperlyConfigured('Union stored procedure not available.')
 

django/contrib/gis/tests/geoapp/tests.py

@@ -172,6 +172,20 @@ class GeoModelTest(unittest.TestCase):
             self.assertAlmostEqual(ptown.x, p.point.x, prec)
             self.assertAlmostEqual(ptown.y, p.point.y, prec)
 
+    @no_oracle # Most likely can do this in Oracle, however, it is not yet implemented (patches welcome!)
+    def test05_extent(self):
+        "Testing the extent() GeoManager method."
+        # Reference query:
+        # `SELECT ST_extent(point) FROM geoapp_city WHERE (name='Houston' or name='Dallas');`
+        #   =>  BOX(-96.8016128540039 29.7633724212646,-95.3631439208984 32.7820587158203)
+        expected = (-96.8016128540039, 29.7633724212646, -95.3631439208984, 32.782058715820)
+
+        qs = City.objects.filter(name__in=('Houston', 'Dallas'))
+        extent = qs.extent()
+
+        for val, exp in zip(extent, expected):
+            self.assertAlmostEqual(exp, val, 8)
+
     def test09_disjoint(self):
         "Testing the `disjoint` lookup type."
         if DISABLE: return

django/contrib/gis/utils/layermapping.py

@@ -112,7 +112,7 @@ from datetime import date, datetime
 from decimal import Decimal
 from django.core.exceptions import ObjectDoesNotExist
 from django.contrib.gis.db.models.fields import GeometryField
-from django.contrib.gis.db.backend import SPATIAL_BACKEND
+from django.contrib.gis.db.backend import SpatialBackend
 from django.contrib.gis.gdal import CoordTransform, DataSource, \
     OGRException, OGRGeometry, OGRGeomType, SpatialReference
 from django.contrib.gis.gdal.field import \
@@ -506,7 +506,7 @@ class LayerMapping(object):
         # Getting the GeometryColumn object.
         try:
             db_table = self.model._meta.db_table
-            if SPATIAL_BACKEND == 'oracle': db_table = db_table.upper()
+            if SpatialBackend.name == 'oracle': db_table = db_table.upper()
             gc_kwargs = {GeometryColumns.table_name_col() : db_table}
             return GeometryColumns.objects.get(**gc_kwargs)
         except Exception, msg: