Function select_related_descend

django/db/models/query_utils.py:431–466

Return whether `field` should be used to descend deeper for `select_related()` purposes. Arguments: * `field` - the field to be checked. Can be either a `Field` or `ForeignObjectRel` instance. * `restricted` - a boolean field, indicating if the field list has been

(field, restricted, requested, select_mask)

def select_related_descend(field, restricted, requested, select_mask):
    """
    Return whether `field` should be used to descend deeper for
    `select_related()` purposes.

    Arguments:
     * `field` - the field to be checked. Can be either a `Field` or
       `ForeignObjectRel` instance.
     * `restricted` - a boolean field, indicating if the field list has been
       manually restricted using a select_related() clause.
     * `requested` - the select_related() dictionary.
     * `select_mask` - the dictionary of selected fields.
    """
    # Only relationships can be descended.
    if not field.remote_field:
        return False
    # Forward MTI parent links should not be explicitly descended as they are
    # always JOIN'ed against (unless excluded by `select_mask`).
    if getattr(field.remote_field, "parent_link", False):
        return False
    # When `select_related()` is used without a `*requested` mask all
    # relationships are descended unless they are nullable.
    if not restricted:
        return not field.null
    # When `select_related(*requested)` is used only fields that are part of
    # `requested` should be descended.
    if field.name not in requested:
        return False
    # Prevent invalid usages of `select_related()` and `only()`/`defer()` such
    # as `select_related("a").only("b")` and `select_related("a").defer("a")`.
    if select_mask and field not in select_mask:
        raise FieldError(
            f"Field {field.model._meta.object_name}.{field.name} cannot be both "
            "deferred and traversed using select_related at the same time."
        )
    return True


def refs_expression(lookup_parts, annotations):