Django 1.9.5: FieldError pour les champs de recherche inversée de temps en temps

Question

Je reçois une erreur intermittente frustrante dans Django, en essayant d'exécuter le objects.all() pour un Queryset qui est préextrayant. Il y a un problème où parfois le model._meta semble être des champs manquants, entre l'instanciation d'un jeu de requête et l'exécution d'une itération à travers lui. C'est presque comme si la préextraction du jeu de requête n'était pas exécutée à temps pour l'itération de la liste des objets.

Dans cet exemple, data.service_log est simplement un jeu de requête avec des éléments préchargés appelés servicelog. Lorsque je lance le jeu de requête dans le shell, je peux regarder tous les champs de la méthode self.names_to_path(lookup_splitted, self.get_meta()) sur le jeu de requête. Ils sont tous là, en particulier le "servicelog".

Notez ce Traceback pour cette erreur, il est dit que "servicelog" n'est pas un champ disponible, mais il le répertorie dans la liste des champs à choisir. Cela semble être un bug Django, mais je ne peux pas en être sûr car je ne peux pas expliquer ou isoler le comportement. Je ne peux pas être la seule personne à avoir cette erreur. Il semble être dans django/db/models/sql/query.py dans la méthode names_to_paths(). Voici le code qui ne parvient pas à résoudre:

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 si le champ est None fails so we enter the autre block. There the pos 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 champ with opts.get_field ('ServiceLog') `. Ce n'est que lorsqu'il est exécuté à partir de WSGI et Apache2 que cet échec se produit. Encore une fois, ce n'est pas tout le temps, ce qui le rend extrêmement difficile à tester. Je suis perplexe par cela, et je ne sais pas où chercher des indices. S'IL VOUS PLAIT si quelqu'un a des idées sur ce qu'il faut explorer, je serais tellement reconnaissant.

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 

MISE À JOUR - l'ajout de modèles/offensant code de vue

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

moi avons eu un problème similaire en utilisant Django 1.8.6 sur gunicorn/Django runserver. Je n'ai pas non plus réussi à reproduire l'erreur dans l'environnement shell/notebook. J'ai résolu l'erreur FieldError aléatoire en ajoutant related_name au ManyToManyField. J'ai utilisé a through model dans le ManyToManyField bien.

Dans votre cas:

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

Jan