Commit b6c356b7 authored by Anssi Kääriäinen's avatar Anssi Kääriäinen
Browse files

Fixed #17485 -- Made defer work with select_related 

This commit tackles a couple of issues. First, in certain cases there
were some mixups if field.attname or field.name should be deferred.
Field.attname is now always used.

Another issue tackled is a case where field is both deferred by
.only(), and selected by select_related. This case is now an error.

A lot of thanks to koniiiik (Michal Petrucha) for the patch, and
to Andrei Antoukh for review.
parent 53187830

django/db/models/query.py

+4 −3
Original line number Diff line number Diff line
@@ -1296,7 +1296,7 @@ def get_klass_info(klass, max_depth=0, cur_depth=0, requested=None, 
        # Build the list of fields that *haven't* been requested

        for field, model in klass._meta.get_fields_with_model():

            if field.name not in load_fields:

                skip.add(field.name)

                skip.add(field.attname)

            elif local_only and model is not None:

                continue

            else:
@@ -1327,7 +1327,7 @@ def get_klass_info(klass, max_depth=0, cur_depth=0, requested=None, 


    related_fields = []

    for f in klass._meta.fields:

        if select_related_descend(f, restricted, requested):

        if select_related_descend(f, restricted, requested, load_fields):

            if restricted:

                next = requested[f.name]

            else:
@@ -1339,7 +1339,8 @@ def get_klass_info(klass, max_depth=0, cur_depth=0, requested=None, 
    reverse_related_fields = []

    if restricted:

        for o in klass._meta.get_all_related_objects():

            if o.field.unique and select_related_descend(o.field, restricted, requested, reverse=True):

            if o.field.unique and select_related_descend(o.field, restricted, requested,

                                                         only_load.get(o.model), reverse=True):

                next = requested[o.field.related_query_name()]

                klass_info = get_klass_info(o.model, max_depth=max_depth, cur_depth=cur_depth+1,

                                            requested=next, only_load=only_load, local_only=True)

django/db/models/query_utils.py

+11 −2
Original line number Diff line number Diff line
@@ -126,18 +126,19 @@ class DeferredAttribute(object): 
        return None





def select_related_descend(field, restricted, requested, reverse=False):

def select_related_descend(field, restricted, requested, load_fields, reverse=False):

    """

    Returns True if this field should be used to descend deeper for

    select_related() purposes. Used by both the query construction code

    (sql.query.fill_related_selections()) and the model instance creation code

    (query.get_cached_row()).

    (query.get_klass_info()).



    Arguments:

     * field - the field to be checked

     * restricted - a boolean field, indicating if the field list has been

       manually restricted using a requested clause)

     * requested - The select_related() dictionary.

     * load_fields - the set of fields to be loaded on this model

     * reverse - boolean, True if we are checking a reverse select related

    """

    if not field.rel:
@@ -151,6 +152,14 @@ def select_related_descend(field, restricted, requested, reverse=False): 
            return False

    if not restricted and field.null:

        return False

    if load_fields:

        if field.name not in load_fields:

            if restricted and field.name in requested:

                raise InvalidQuery("Field %s.%s cannot be both deferred"

                                   " and traversed using select_related"

                                   " at the same time." %

                                   (field.model._meta.object_name, field.name))

            return False

    return True



# This function is needed because data descriptors must be defined on a class

django/db/models/sql/compiler.py

+5 −2
Original line number Diff line number Diff line
@@ -596,6 +596,7 @@ class SQLCompiler(object): 
        if avoid_set is None:

            avoid_set = set()

        orig_dupe_set = dupe_set

        only_load = self.query.get_loaded_field_names()



        # Setup for the case when only particular related fields should be

        # included in the related selection.
@@ -607,7 +608,8 @@ class SQLCompiler(object): 
                restricted = False



        for f, model in opts.get_fields_with_model():

            if not select_related_descend(f, restricted, requested):

            if not select_related_descend(f, restricted, requested,

                                          only_load.get(model or self.query.model)):

                continue

            # The "avoid" set is aliases we want to avoid just for this

            # particular branch of the recursion. They aren't permanently
@@ -680,7 +682,8 @@ class SQLCompiler(object): 
                if o.field.unique

            ]

            for f, model in related_fields:

                if not select_related_descend(f, restricted, requested, reverse=True):

                if not select_related_descend(f, restricted, requested,

                                              only_load.get(model), reverse=True):

                    continue

                # The "avoid" set is aliases we want to avoid just for this

                # particular branch of the recursion. They aren't permanently

django/db/models/sql/query.py

+9 −3
Original line number Diff line number Diff line
@@ -1845,8 +1845,14 @@ class Query(object): 


        If no fields are marked for deferral, returns an empty dictionary.

        """

        # We cache this because we call this function multiple times

        # (compiler.fill_related_selections, query.iterator)

        try:

            return self._loaded_field_names_cache

        except AttributeError:

            collection = {}

            self.deferred_to_data(collection, self.get_loaded_field_names_cb)

            self._loaded_field_names_cache = collection

            return collection



    def get_loaded_field_names_cb(self, target, model, fields):

docs/ref/models/querysets.txt

+8 −3
Original line number Diff line number Diff line
@@ -1081,11 +1081,13 @@ to ``defer()``:: 
    # Load all fields immediately.

    my_queryset.defer(None)



.. versionchanged:: 1.5



Some fields in a model won't be deferred, even if you ask for them. You can

never defer the loading of the primary key. If you are using

:meth:`select_related()` to retrieve related models, you shouldn't defer the

loading of the field that connects from the primary model to the related one

(at the moment, that doesn't raise an error, but it will eventually).

loading of the field that connects from the primary model to the related

one, doing so will result in an error.



.. note::
@@ -1145,9 +1147,12 @@ logically:: 
    # existing set of fields).

    Entry.objects.defer("body").only("headline", "body")



.. versionchanged:: 1.5



All of the cautions in the note for the :meth:`defer` documentation apply to

``only()`` as well. Use it cautiously and only after exhausting your other

options.

options. Also note that using :meth:`only` and omitting a field requested

using :meth:`select_related` is an error as well.



using

~~~~~