foreign-key-relationship

问题 I have a Foreign Key from one model into another model in a differente database (I know I shouldn't do it but if I take care properly of Referential Integrity it shouldn't be a problem). The thing is that everything works fine...all the system does (relationships on any direction, the router takes care of it) but when I try to delete the referenced model (which doesn't have the foreign key attribute)...Django still wants to go throught the relationship to check if the relationship is empty,

问题 I have a Foreign Key from one model into another model in a differente database (I know I shouldn't do it but if I take care properly of Referential Integrity it shouldn't be a problem). The thing is that everything works fine...all the system does (relationships on any direction, the router takes care of it) but when I try to delete the referenced model (which doesn't have the foreign key attribute)...Django still wants to go throught the relationship to check if the relationship is empty,

问题 I have a Foreign Key from one model into another model in a differente database (I know I shouldn't do it but if I take care properly of Referential Integrity it shouldn't be a problem). The thing is that everything works fine...all the system does (relationships on any direction, the router takes care of it) but when I try to delete the referenced model (which doesn't have the foreign key attribute)...Django still wants to go throught the relationship to check if the relationship is empty,

问题 I have a Foreign Key from one model into another model in a differente database (I know I shouldn't do it but if I take care properly of Referential Integrity it shouldn't be a problem). The thing is that everything works fine...all the system does (relationships on any direction, the router takes care of it) but when I try to delete the referenced model (which doesn't have the foreign key attribute)...Django still wants to go throught the relationship to check if the relationship is empty,

问题 I'm designing a database for a web application project and I came to the conclusion I may have few queries that will require a lot of joined tables to just make one check. I'm wondering how bad is it to store the foreign key somewhere on the way to decrease number of joins required for these queries? To give you an example of what I have at this moment: Service => Booking => Transaction => Wallet => BonusOffer I need to check whether the service has been bought with wallet associated with a

问题 I'm designing a database for a web application project and I came to the conclusion I may have few queries that will require a lot of joined tables to just make one check. I'm wondering how bad is it to store the foreign key somewhere on the way to decrease number of joins required for these queries? To give you an example of what I have at this moment: Service => Booking => Transaction => Wallet => BonusOffer I need to check whether the service has been bought with wallet associated with a

问题 Suppose I have the following in my models.py: class Book: pass class Part: book = models.ForeignKey(Book) class Chapter: part = models.ForeignKey(Part) number = models.IntegerField() I would like to do book = Book.objects.get(id=someID) chapters = Book.chapters.get(number=4) What is a clean way to do so? I thought of a Manager on the book class but it doest not seem to work for this case. Of course I could implement a method get_chapters on class book but i would like to avoid this. any ideas

问题 Suppose I have the following in my models.py: class Book: pass class Part: book = models.ForeignKey(Book) class Chapter: part = models.ForeignKey(Part) number = models.IntegerField() I would like to do book = Book.objects.get(id=someID) chapters = Book.chapters.get(number=4) What is a clean way to do so? I thought of a Manager on the book class but it doest not seem to work for this case. Of course I could implement a method get_chapters on class book but i would like to avoid this. any ideas

问题 I'm pretty new to working with SQL but I've come across this question on Stack Overflow for working with tags. Recommended SQL database design for tags or tagging This led me to create the following tables in my database: Doc --------------------------------------------------------------- | Doc Id (PK)(int) | Doc Title (varchar) | Doc Link (varchar) | --------------------------------------------------------------- | 1 | Printing | http://example.com | -----------------------------------------

问题 I have tow models like below: class A(models.Model): a = models.BooleanField(default=False) q = models.BooleanField(default=False) class B(models.Model): c = models.Foreignkey('A', related_name='bb') d = models.BooleanField(default=False) e = models.BooleanField(default=False) Here is my view: class Myview(ListView): model = A template_name = 'admin/layer.html' def get_context_data(self, *args, **kwargs): context = super(ListView, self).get_context_data(*args, **kwargs) context['mylist'] = A