functions.py 文件源码

def as_postgresql(self, compiler, connection):
        geo_field = GeometryField(srid=self.srid)  # Fake field to get SRID info
        src_field = self.get_source_fields()[0]
        geography = src_field.geography and self.srid == 4326
        if geography:
            self.source_expressions.append(Value(self.spheroid))
        elif geo_field.geodetic(connection):
            # Geometry fields with geodetic (lon/lat) coordinates need length_spheroid
            self.function = 'ST_Length_Spheroid'
            self.source_expressions.append(Value(geo_field._spheroid))
        else:
            dim = min(f.dim for f in self.get_source_fields() if f)
            if dim > 2:
                self.function = connection.ops.length3d
        return super(Length, self).as_sql(compiler, connection)