Function _instance_processor

lib/sqlalchemy/orm/loading.py:812–1254

Produce a mapper level row processor callable which processes rows into mapped instances.

(
    query_entity,
    mapper,
    context,
    result,
    path,
    adapter,
    only_load_props=None,
    refresh_state=None,
    polymorphic_discriminator=None,
    _polymorphic_from=None,
)

def _instance_processor(
    query_entity,
    mapper,
    context,
    result,
    path,
    adapter,
    only_load_props=None,
    refresh_state=None,
    polymorphic_discriminator=None,
    _polymorphic_from=None,
):
    """Produce a mapper level row processor callable
    which processes rows into mapped instances."""

    # note that this method, most of which exists in a closure
    # called _instance(), resists being broken out, as
    # attempts to do so tend to add significant function
    # call overhead.  _instance() is the most
    # performance-critical section in the whole ORM.

    identity_class = mapper._identity_class
    compile_state = context.compile_state

    # look for "row getter" functions that have been assigned along
    # with the compile state that were cached from a previous load.
    # these are operator.itemgetter() objects that each will extract a
    # particular column from each row.

    getter_key = ("getters", mapper)
    getters = path.get(compile_state.attributes, getter_key, None)

    if getters is None:
        # no getters, so go through a list of attributes we are loading for,
        # and the ones that are column based will have already put information
        # for us in another collection "memoized_setups", which represents the
        # output of the LoaderStrategy.setup_query() method.  We can just as
        # easily call LoaderStrategy.create_row_processor for each, but by
        # getting it all at once from setup_query we save another method call
        # per attribute.
        props = mapper._prop_set
        if only_load_props is not None:
            props = props.intersection(
                mapper._props[k] for k in only_load_props
            )

        quick_populators = path.get(
            context.attributes, "memoized_setups", EMPTY_DICT
        )

        todo = []
        cached_populators = {
            "new": [],
            "quick": [],
            "deferred": [],
            "expire": [],
            "existing": [],
            "eager": [],