Django - impossible d'importer mes propres modèles

Question

J'ai plusieurs applications Django, toutes dans un répertoire de projet. Chaque application a un fichier models.py avec un tas de modèles. J'ai importé des modèles d'une application à l'autre sans problème, en particulier pour créer un nouveau modèle avec un champ de clé étrangère, pointant vers le modèle dans l'autre application. Pas de problème jusqu'à présent.

J'ai décidé de créer un nouveau modèle. Il a 4 champs ForeignKey, chacun pointant vers un modèle différent dans une application différente. Simple. Cependant, lorsque j'essaie d'utiliser south pour migrer le schéma vers la base de données, il m'indique qu'il ne peut pas importer mes modèles. Pourquoi?!

Alors, voici mon nouveau modèle:

class Action_Tracker(models.Model): 
    dateOfAction = models.DateField(verbose_name = 'Date of Action') 
    user = models.CharField(max_length=30, verbose_name = 'Action completed by') 
    sys = models.ForeignKey(System, verbose_name='For System') 
    wo = models.ForeignKey(Work_Order, verbose_name='Associated WO', blank=True, null=True) 
    inv = models.ForeignKey(Invoice, verbose_name = 'Associated Invoice', blank=True, null=True) 
    subdT = models.ForeignKey(SUBD_Tracker, verbose_name = 'Associated SUBD Tracker', blank=True, null=True) 
    notes = models.TextField(verbose_name='Notes of Action', blank=True, null=True) 

    def __unicode__(self): 
     return u'%s -- %s' % (self.dateOfAction, self.notes) 

    class Meta: 
     orering = ['dateOfAction'] 

Au sommet de ce fichier models.py je les importations suivantes:

from django.db import models 
from django.forms import ModelForm, forms 
from staff.models import Employee, Position 
from work_orders.models import Work_Order, SUBD_Tracker 
from invoices.models import Invoice 

D'après ce que je peux dire, je am importation ceux-ci correctement. Cependant, lorsque je tente de faire une migration de schéma, je reçois l'erreur suivante:

File "/srv/www/cpm/../cpm/systems/models.py", line 4, in <module> 
    from work_orders.models import Work_Order, SUBD_Tracker 
File "/srv/www/cpm/work_orders/models.py", line 5, in <module> 
    from systems.models import System 
File "/srv/www/cpm/systems/models.py", line 4, in <module> 
    from work_orders.models import Work_Order, SUBD_Tracker 
ImportError: cannot import name Work_Order 

Toute idée de ce qui va mal ici ??

Merci

EDIT - sur demande

Je poste le code work_order models.py tel que demandé (au moins, les parties pertinentes):

from django.db import models 
from django.forms import ModelForm, forms 
from django import forms 
from products.models import Product 
from systems.models import System 
from labour.models import Labour_Costs 
from staff.models import Employee 
from datetime import date 
import datetime 

class Work_Order(models.Model): 
    IS_COMPLETE_CHOICES = (
     ('Y', 'Yes'), 
     ('N', 'No'), 
    ) 

    INVOICE_CREATED_CHOICES = (
     ('Y', 'Yes, mark WO complete and generate invoice (if applicable)'), 
     ('N', 'No, just save these changes'), 
    ) 

    WO_TYPE_CHOICES = (
     ('M', 'Mechanical'), 
     ('I', 'Install'), 
     ('S', 'Show'), 
     ('R', 'Service'), 
     ('B', 'Blow down'), 
     ('U', 'Start up'), 
    ) 

    woID = models.CharField(max_length = 25, primary_key = True, verbose_name = 'Work Order ID') 
    woType = models.CharField(max_length = 2, verbose_name = 'WO Type', default='R', choices = WO_TYPE_CHOICES) 
    systemID = models.ForeignKey(System, verbose_name = 'System ID') 
    notesToCrew = models.TextField(blank = True, null = True, verbose_name = 'Notes to Crew') 
    dateWOCreated = models.DateField(blank = True, null = True, default=datetime.date.today(), verbose_name = 'Date Created') 
    dateWORequired = models.DateField(blank = True, null = True, verbose_name = 'Date Required') 
    dateCompleted = models.DateField(blank = True, null = True, verbose_name = 'Date Completed') 
    numDays = models.DecimalField(max_digits = 3, decimal_places = 0, verbose_name = 'Number of Days to Complete', blank = True, null = True) 
    numHours = models.DecimalField(max_digits = 3, decimal_places = 2, verbose_name = 'Number of Hours to Complete', blank = True, null = True) 
    isComplete = models.CharField (max_length = 3, default = 'N', verbose_name = 'Set WO as Completed?', choices = IS_COMPLETE_CHOICES) 
    isScheduled = models.CharField (max_length = 3, default = 'N', verbose_name = 'Is WO scheduled?', choices = IS_COMPLETE_CHOICES) 
    isReqSoon = models.BooleanField(default=False, verbose_name='Is WO Required soon') #This flag will be set in a function to indicate that the WO is reqd within the current week/few days, whatever 
    problemDescription = models.TextField(verbose_name = 'Problem Description', blank = True, null = True) 
    resolution = models.TextField(verbose_name = 'Resolution', blank = True, null = True) 
    serviceFromBD = models.TextField(verbose_name = 'Service issues noticed', blank = True, null = True) 
    serviceFromBDEstTime = models.DecimalField(max_digits = 3, decimal_places = 2, verbose_name = 'Est. Time to Repair', blank = True, null = True) 
    numWorkers = models.DecimalField(max_digits = 3, default=1, decimal_places = 0, verbose_name = 'Number of Workers Required', blank = True, null = True) 
    invoiceCreated = models.CharField (max_length = 3, default = 'N', verbose_name = 'Generate Invoice?', choices = INVOICE_CREATED_CHOICES) 

    def __unicode__(self): 
     return u'%s - %s' % (self.woID, self.systemID.systemAddress) 

    class Meta: 
     ordering = ['woID'] 


class SUBD_Tracker(models.Model): 
    SUBD_CHOICES = (
     ('U', 'Startup'), 
     ('B', 'Blowdown'), 
    ) 

    sys = models.ForeignKey(System, verbose_name = 'Related System') 
    subd = models.CharField(max_length=1, verbose_name = 'SU or BD', choices = SUBD_CHOICES) 
    ssn = models.CharField(max_length=5, verbose_name = 'Season') 
    approved = models.BooleanField(verbose_name = 'Approved', default = False) 
    declined = models.BooleanField(verbose_name = 'Declined', default = False) 
    cancelled = models.BooleanField(verbose_name = 'Cancel', default = False) 
    firstNoticeSent = models.BooleanField(verbose_name = 'First Notice Sent?', default = False) 
    secondNoticeSent = models.BooleanField(verbose_name = 'Second Notice Sent?', default = False) 
    wo = models.ForeignKey(Work_Order, verbose_name = 'Related WO', blank = True, null = True) 

    def __unicode__(self): 
     if self.subd == 'U': 
      return u'%s: Startup - %s' % (self.sys, self.ssn) 
     else: 
      return u'%s: Blowdown - %s' % (self.sys, self.ssn) 

    class Meta: 
     ordering = ['sys'] 

Answer 1

Si vous lisez le ForeignKey documentation, vous verrez que le premier argument peut être une chaîne. Cela vous permet de créer vos clés étrangères sans avoir à importer, contourner le problème de référence circulaire.

Ainsi, votre modèle deviendrait alors:

class Action_Tracker(models.Model): 
    dateOfAction = models.DateField(verbose_name = 'Date of Action') 
    user = models.CharField(max_length=30, verbose_name = 'Action completed by') 
    sys = models.ForeignKey('systems.System', verbose_name='For System') 
    wo = models.ForeignKey('work_orders.Work_Order', verbose_name='Associated WO', blank=True, null=True) 
    inv = models.ForeignKey('invoices.Invoice', verbose_name = 'Associated Invoice', blank=True, null=True) 
    subdT = models.ForeignKey('work_orders.SUBD_Tracker', verbose_name = 'Associated SUBD Tracker', blank=True, null=True) 
    notes = models.TextField(verbose_name='Notes of Action', blank=True, null=True) 

    def __unicode__(self): 
     return u'%s -- %s' % (self.dateOfAction, self.notes) 

    class Meta: 
     ordering = ['dateOfAction'] 

Aucune déclaration d'importation requis!