django-models

问题 I have been read some Django document about inheritance models and parent_link . Suppose that I have these models: class Parent(models.Model): #Some field goes here! class Child(Parent): #Some field goes here! I have 3 questions about this pattern: What should I do if I want to create new child object and pass id of existing parent to that? What should I do if I want to create just new child object and after a while create parent object for that child? Also I din't understand this document

问题 I've looked through the similar questions and was unable to find a solution that fits or I'm missing something? I have two models(SafetyCourse and SafetyCourseTaken) I have a foreign key relationship that points from "safety courses taken" to safety course, shown below: models.py class SafetyCourse(models.Model): user = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE) name = models.CharField(max_length=128, unique=True) def __str__(self): return self.name class

问题 I've looked through the similar questions and was unable to find a solution that fits or I'm missing something? I have two models(SafetyCourse and SafetyCourseTaken) I have a foreign key relationship that points from "safety courses taken" to safety course, shown below: models.py class SafetyCourse(models.Model): user = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE) name = models.CharField(max_length=128, unique=True) def __str__(self): return self.name class

问题 I've looked through the similar questions and was unable to find a solution that fits or I'm missing something? I have two models(SafetyCourse and SafetyCourseTaken) I have a foreign key relationship that points from "safety courses taken" to safety course, shown below: models.py class SafetyCourse(models.Model): user = models.ForeignKey(settings.AUTH_USER_MODEL, on_delete=models.CASCADE) name = models.CharField(max_length=128, unique=True) def __str__(self): return self.name class

问题 I'm using django 1.8 and I'm having problems adding to my models.py. Currently it's: from django.db import models # Create your models here. class Company(models.Model): role = models.CharField(max_length=32, blank=True) name = models.CharField(max_length=70, blank=True) and it works perfectly fine but whenever I try to add to this and then run the server I get OperationalError: no such column [added element] For example I added founder = models.CharField(max_length=200, blank=True) and I ran

问题 I have a table like this Event table | id | status | date |order(FK)| | 1 | Planned | 05-02-2015 | 1 | | 2 | Delivered | 04-02-2015 | 2 | | 3 | Packed | 03-02-2015 | 3 | | 4 | Return | 06-02-2015 | 1 | I want output like this | id | status | date |order(FK)| | 2 | Delivered | 04-02-2015 | 2 | | 3 | Packed | 03-02-2015 | 3 | | 4 | Return | 06-02-2015 | 1 | I tried with query = Event.objects.annotate(order_num=Max('date')) but didn't got the expected result. How can i achieve this output 回答1:

问题 How should I write a type hint for class types in Python? Consider this code: class A(object): pass class B(A): pass def register(cls: type[A]): assert issubclass(cls, A) register(A) register(B) Is type[A] the correct way to write this? If I'd just use cls: A it would mean cls is an instance of A , but I want to to say cls is a class/type, which at least subclasses A . Specifically, what I want to indicate is that the parameter should be a Django model type. 回答1: It seems like other current

问题 How should I write a type hint for class types in Python? Consider this code: class A(object): pass class B(A): pass def register(cls: type[A]): assert issubclass(cls, A) register(A) register(B) Is type[A] the correct way to write this? If I'd just use cls: A it would mean cls is an instance of A , but I want to to say cls is a class/type, which at least subclasses A . Specifically, what I want to indicate is that the parameter should be a Django model type. 回答1: It seems like other current

问题 (I'm new to Django, Python, and Postgresql) I've been adding and deleting data in my development and noticed that the pk keeps adding up and never reset to 1 even if I delete all the models. Is it possible to reset the pk to start from 1 before I push this up to the production? Is it a good idea to do that? 回答1: You can reset model id sequence using sqlsequencereset command python manage.py sqlsequencereset myapp1 myapp2 myapp3| psql If you want to read the generated sql command, just execute

问题 How to work with Django models inside Airflow tasks? According to official Airflow documentation, Airflow provides hooks for interaction with databases (like MySqlHook / PostgresHook / etc) that can be later used in Operators for row query execution. Attaching the core code fragments: Copy from https://airflow.apache.org/_modules/mysql_hook.html class MySqlHook(DbApiHook): conn_name_attr = 'mysql_conn_id' default_conn_name = 'mysql_default' supports_autocommit = True def get_conn(self): """