Bulkload post_import_function that shims in a repeated StructuredProperty.

gistfile1.py

def add_polygons(input_dict, instance, bulkload_state_copy):    
    """Bulkload post_import_function that shims in a repeated StructuredProperty.
    
    This function allows us to bulkload a StructuredProperty model using the App
    Engine bulkloader by adding the following lines to the bulkload.yaml 
    configuration file:

        - kind: LayerIndex
          connector: csv
          connector_options:
            encoding: utf_8
          property_map: 
            - property: __key__
              external_name: id
          post_import_function: our_bulkloader_transforms.add_polygons

    Then, given our LayerPolygon model:

        class LayerPolygon(model.Model): 
            polygonid = model.StringProperty(required=True)
            areaid = model.StringProperty(required=True)
            specieslatin = model.StringProperty(required=True)
            source = model.StringProperty(required=True)
    
    We create a StructuredProperty in our LayerIndex model:

        class LayerIndex(model.Expando): 
            polygons = model.StructuredProperty(LayerPolygon, repeated=True)

    After the bulkload we can filter for the StructuredProperty field values as 
    described in the Datastore Plus Tutorial, Part One (http://goo.gl/ky5sa). For 
    example:

        qry = LayerIndex.query(
            LayerIndex.polygons == LayerPolygon(
                specieslatin='puma concolor', polygonid=2))

    """

    # Model the LayerPolygon properties as parallel arrays
    polygonid = []
    areaid = []
    specieslatin = []
    source = []
    
    # Populate the parallel arrays from values in the input_dict (a CSV row)
    polygons = simplejson.loads(input_dict['polygons'])
    for p in polygons:
        polygonid.append(p['polygonid'])
        areaid.append(p['areaid'])
        specieslatin.append(p['specieslatin'])
        source.append(p['source'])
    
    # Update entity instance with new property names that match the StructuredProperty
    instance['polygons.polygonid'] = polygonid
    instance['polygons.areaid'] = areaid
    instance['polygons.specieslatin'] = specieslatin
    instance['polygons.source'] = source

    return instance