Django 1.9.5: FieldError для полей обратного поиска иногда

Question

Я получаю разочаровывающую прерывистую ошибку в Django при попытке запустить objects.all() для Queryset, который является предварительной выборкой. Существует проблема, когда иногда model._meta, кажется, отсутствует поля, между экземпляром запроса и запуском итерации через него. Это почти так, как будто предварительная выборка запроса не запускается вовремя для итерации списка объектов.

В этом примере data.service_log - это просто набор запросов с некоторыми предварительно загруженными элементами, которые называются servicelog. Когда я запускаю запрос в оболочке, я могу просмотреть все поля в методе self.names_to_path(lookup_splitted, self.get_meta()) в запросе. Они все там, в частности, «servicelog».

Обратите внимание на этот ответ на эту ошибку. В нем говорится, что «servicelog» не является доступным полем, но он перечисляет его в списке полей на выбор. Кажется, это ошибка Django, но я не могу быть уверен, потому что я не могу объяснить или изолировать поведение. Я не могу быть единственным человеком, получающим эту ошибку. Кажется, что он находится в django/db/models/sql/query.py в методе names_to_paths(). Вот код, который не в состоянии решить:

query.py names_to_paths(): 

field = None 
try: 
    field = opts.get_field(name) 
except FieldDoesNotExist: 
    if name in self.annotation_select: 
     field = self.annotation_select[name].output_field 

if field is not None: 
    # Fields that contain one-to-many relations with a generic 
    # model (like a GenericForeignKey) cannot generate reverse 
    # relations and therefore cannot be used for reverse querying. 
    if field.is_relation and not field.related_model: 
     raise FieldError(
      "Field %r does not generate an automatic reverse " 
      "relation and therefore cannot be used for reverse " 
      "querying. If it is a GenericForeignKey, consider " 
      "adding a GenericRelation." % name 
     ) 
    try: 
     model = field.model._meta.concrete_model 
    except AttributeError: 
     model = None 
else: 
    # We didn't find the current field, so move position back 
    # one step. 
    pos -= 1 
    if pos == -1 or fail_on_missing: 
     field_names = list(get_field_names_from_opts(opts)) 
     available = sorted(field_names + list(self.annotation_select)) 
     raise FieldError("Cannot resolve keyword %r into field. " 
         "Choices are: %s" % (name, ", .join(available))) 
    break 

field does not get set in the first try, then the condition statement, если поле не является None fails so we enter the еще block. There the пос gets reduced by one, but since this field is 'servicelog' it is already at 0. However, when I try this in the shell, it always finds the поле with opts.get_field ('servicelog') `. Только при запуске из WSGI и Apache2 происходит этот сбой. Опять же, это не все время, что делает его чрезвычайно трудным для тестирования. Я недоумеваю, и не знаю, где искать подсказки. ПОЖАЛУЙСТА, если у кого-то есть ЛЮБОЕ представление о том, что нужно исследовать, я буду так благодарен.

Traceback (most recent call last): 

    File "/var/www/fast/services/views/edit.py", line 12897, in service_log 
    for service in data.service_log: 

    File "/usr/local/lib/python2.7/dist-packages/django/db/models/query.py", line 258, in __iter__ 
    self._fetch_all() 

    File "/usr/local/lib/python2.7/dist-packages/django/db/models/query.py", line 1076, in _fetch_all 
    self._prefetch_related_objects() 

    File "/usr/local/lib/python2.7/dist-packages/django/db/models/query.py", line 656, in _prefetch_related_objects 
    prefetch_related_objects(self._result_cache, self._prefetch_related_lookups) 

    File "/usr/local/lib/python2.7/dist-packages/django/db/models/query.py", line 1457, in prefetch_related_objects 
    obj_list, additional_lookups = prefetch_one_level(obj_list, prefetcher, lookup, level) 

    File "/usr/local/lib/python2.7/dist-packages/django/db/models/query.py", line 1556, in prefetch_one_level 
    prefetcher.get_prefetch_queryset(instances, lookup.get_current_queryset(level))) 

    File "/usr/local/lib/python2.7/dist-packages/django/db/models/fields/related_descriptors.py", line 802, in get_prefetch_queryset 
    queryset = queryset._next_is_sticky().filter(**query) 

    File "/usr/local/lib/python2.7/dist-packages/django/db/models/query.py", line 790, in filter 
    return self._filter_or_exclude(False, *args, **kwargs) 

    File "/usr/local/lib/python2.7/dist-packages/django/db/models/query.py", line 808, in _filter_or_exclude 
    clone.query.add_q(Q(*args, **kwargs)) 

    File "/usr/local/lib/python2.7/dist-packages/django/db/models/sql/query.py", line 1243, in add_q 
    clause, _ = self._add_q(q_object, self.used_aliases) 

    File "/usr/local/lib/python2.7/dist-packages/django/db/models/sql/query.py", line 1269, in _add_q 
    allow_joins=allow_joins, split_subq=split_subq, 

    File "/usr/local/lib/python2.7/dist-packages/django/db/models/sql/query.py", line 1149, in build_filter 
    lookups, parts, reffed_expression = self.solve_lookup_type(arg) 

    File "/usr/local/lib/python2.7/dist-packages/django/db/models/sql/query.py", line 1035, in solve_lookup_type 
    _, field, _, lookup_parts = self.names_to_path(lookup_splitted, self.get_meta()) 

    File "/usr/local/lib/python2.7/dist-packages/django/db/models/sql/query.py", line 1330, in names_to_path 
    "Choices are: %s" % (name, ", ".join(available))) 

FieldError: Cannot resolve keyword u'servicelog' into field. Choices are: additional_county_worker_notes, adoption_disrupted, adoption_first_name, adoption_last_name, adoption_middle_name, adoption_placement_date, adoption_placement_reason, adoption_placement_reason_id, adoption_placement_type, adoption_risk_level, adoption_risk_level_id, adoption_termination_date, adoption_termination_destination, adoption_termination_reason, adoption_termination_reason_id, adoptive_placement, agency, agency_id, all_items_outstanding, all_items_past_due, appeal_process_date, attached_file, attends_college, attorney_email_address, attorney_email_address_id, attorney_fax, attorney_fax_id, attorney_investigator_email_address, attorney_investigator_email_address_id, attorney_investigator_fax, attorney_investigator_fax_id, attorney_investigator_name, attorney_investigator_phone, attorney_investigator_phone_id, attorney_name, attorney_phone, attorney_phone_id, blood_related_to_applicants, blood_relationship, casa_email_address, casa_email_address_id, casa_fax, casa_fax_id, casa_name, casa_phone, casa_phone_id, certification_items_outstanding, certification_items_past_due, classification, classification_id, client, client_id, county_adoption_worker, county_adoption_worker_cell, county_adoption_worker_cell_id, county_adoption_worker_email_address, county_adoption_worker_email_address_id, county_adoption_worker_fax, county_adoption_worker_fax_id, county_adoption_worker_office, county_adoption_worker_office_id, county_adoption_worker_phone, county_adoption_worker_phone_id, county_adoption_worker_title, county_case_number, county_worker, county_worker_cell, county_worker_cell_id, county_worker_email_address, county_worker_email_address_id, county_worker_fax, county_worker_fax_id, county_worker_office, county_worker_office_id, county_worker_phone, county_worker_phone_id, county_worker_title, court, court_case_name, court_case_number, court_department, court_id, created, current_grade, date_identified_adoptive, date_placed_with_home, deleted, discharge_summary, eligibility_worker, eligibility_worker_email_address, eligibility_worker_email_address_id, eligibility_worker_phone, eligibility_worker_phone_id, emergency_placement, employed_80_hours, enable_discharge_summary, expected_type, expected_type_id, extended_family_contact_allowed, final_payment_amount, finalization_date, foreign_placement, hearing_36626_date, homestudy, id, incident_placement_1, incident_placement_2, incident_placement_3, incident_placement_4, individualized_plan_review, inhousemove, interpretive_summary, item_due, items_approved, items_pending, items_rejected, items_update_requested, la_county_id, medi_cal, medi_cal_eligibility_phone, medi_cal_eligibility_phone_id, medi_cal_eligibility_worker, medi_cal_id, modified, monthly_monitored_visit_hours, mother_child, move_in_type, move_out_type, new_protective_custody_petition, non_minor_dependent, non_truant, notes, number_of_files_required, other_school_contact, other_school_contact_first_name, other_school_contact_last_name, parent_payment_override_annually, parent_payment_override_daily, parent_payment_override_monthly, parental_contact_allowed, parental_group, parental_group_id, payment_amount, percent_certified, percent_items_complete, person_number, placement, placement_date, placement_id, placement_payment_override_annually, placement_payment_override_daily, placement_payment_override_monthly, placement_reason, placement_reason_details, placement_reason_id, placement_self, placer_shelter_bed, prior_placement, progress_summary, projected_adoption_36626_date, projected_adoption_finalization_date, projected_adoption_placement_date, recordreview, requires_educational_support, requires_mental_health_services, respite, school, school_different, school_id, school_liaison_email, school_liaison_first_name, school_liaison_last_name, school_liaison_phone, school_liaison_phone_extension, school_notes, serial_number, servicecontact_onbehalf, servicedeliverylog, servicelog, social_worker_at_termination, social_worker_at_termination_id, special_health_care_needs, state_case_number, teachers, termination_date, termination_destination, termination_reason, termination_reason_details, termination_reason_id, therapist, therapy_code, therapy_supervision_requirements, treatment_abilities, treatment_needs, treatment_preferences, treatment_strengths, treatmentneed, update_requested, update_requested_by, update_requested_by_id, update_requested_date, update_requested_note, updateable, use_number_required, uses_psychotropic_medication, visit_frequency_override, visit_frequency_override_id, visitation_restrictions, who_can_pickup_at_home, who_can_pickup_at_school, who_can_visit 

UPDATE - добавление модели/обижая код вид

models.py 
class ParentalGroup(models.Model): 
    many fields... 

class Placement(models.Model): 
    parental_group = models.ForeignKey(ParentalGroup, null=True, blank=True) 
    many more fields... 

class ServiceLog(models.Model): 
    parental_group = models.ForeignKey(ParentalGroup, null=True, blank=True) 
    placement = models.ManyToManyField(Placement, blank=True) 
    many more fields... 


views.py: 
data.service_log = ServiceLog.objects.filter(
    parental_group=data.pg, 
).prefetch_related(
    Prefetch(
     'placement', 
     queryset=Placement.objects.all(), 
     to_attr='placements' 
    ), 
) 

for service in data.service_log: 
    some code to generate data to pass to template... 

return render_to_response(...) 

Answer 1

У меня была аналогичная проблема с использованием Django 1.8.6 на Gunicorn/Django runserver. Мне также не удалось воспроизвести ошибку в среде оболочки/ноутбука.

Я решил случайный FieldError, добавив related_name в ManyToManyField. Я использовал a through model в ManyToManyField.

В вашем случае:

class ServiceLog(models.Model): 
    parental_group = models.ForeignKey(ParentalGroup, null=True, blank=True) 
    placement = models.ManyToManyField(Placement, blank=True, related_name='servicelog') 

Jan