gistfile1.txt

# turn a django model into a mapnik datasource
def model_to_mapnik_ds(model,geom_name=None):
    params = {'user':settings.DATABASE_USER,
        'dbname':settings.DATABASE_NAME,
        'password':settings.DATABASE_PASSWORD,
        'user':settings.DATABASE_USER
        }
    if geom_name:
        geom_field = [f for f in model._meta.fields if f.name == geom_name][0]    
    else:
        geom_field = [f for f in model._meta.fields if isinstance(f, GeometryField)][0]
    params['estimate_extent'] = False
    params['extent'] = '%s,%s,%s,%s' % model.objects.extent(field_name=geom_field.name)
    params['table'] = str(model._meta.db_table)
    params['geometry_field'] = geom_field.name
    params['srid'] = geom_field.srid
    ds = mapnik.PostGIS(**params)
    ds.srs = SpatialReference(geom_field.srid).proj4
    ds.geom_type = geom_field.geom_type.lower()
    return ds

# helper to convert a queryset's sql (to-be) into a mapnik datasource SQL query for the 'table' param
def get_mapnik_sql(qs):
     cols, sql, args = qs._get_sql_clause()
     raw_sql = "(SELECT %s %s) as django_table" % (', '.join(cols),  
sql % tuple(args))
     unquoted_sql = raw_sql.replace('"', '')
     return unquoted_sql