foreign-keys

I have extended Django's User Model using a custom user profile called UserExtension . It is related to User through a unique ForeignKey Relationship, which enables me to edit it in the admin in an inline form! I'm using a signal to create a new profile for every new user: def create_user_profile(sender, instance, created, **kwargs): if created: try: profile, created = UserExtension.objects.get_or_create(user=instance) except: pass post_save.connect(create_user_profile, sender=User) (as described here for example: Extending the User model with custom fields in Django ) The problem is, that, if

I am trying to create database for gym management system, but I can't figure out why I am getting this error. I've tried to search for the answer here, but I couldn't find it. ERROR 1215 (HY000): Cannot add foreign key constraint CREATE TABLE sales( saleId int(100) NOT NULL AUTO_INCREMENT, accountNo int(100) NOT NULL, payName VARCHAR(100) NOT NULL, nextPayment DATE, supplementName VARCHAR(250), qty int(11), workoutName VARCHAR(100), sDate datetime NOT NULL DEFAULT NOW(), totalAmount DECIMAL(11,2) NOT NULL, CONSTRAINT PRIMARY KEY(saleId, accountNo, payName), CONSTRAINT FOREIGN KEY(accountNo)

I'm trying to understand a concept rather than fixing a piece of code that won't work. I'll take a general example of a form (parent table) and a form field (child table). Logically , this would be an identifying relationship, since a form field cannot exist without a form. This would make me think that in order to translate the logical relationship into the technical relationship, a simple NOT NULL for the form_id field in the form_field table would suffice. (See the left part of above screenshot.) However, when I add an identifying relationship using MySQL Workbench, form_id is not only NOT

I have a table called PX_Child that has a foreign key on PX_Parent. I'd like to temporarily disable this FK constraint so that I can truncate PX_Parent. I'm not sure how this goes however. I've tried these commands ALTER TABLE PX_Child NOCHECK CONSTRAINT ALL ALTER TABLE PX_Parent NOCHECK CONSTRAINT ALL (truncate commands) ALTER TABLE PX_Child CHECK CONSTRAINT ALL ALTER TABLE PX_Parent CHECK CONSTRAINT ALL But the truncate still tells me it can't truncate PX_Parent because of a foreign key constraint. I've looked all around the net and can't seem to find what I'm doing wrong, sorry for the

What's the difference in a MySQL FK between RESTRICT and NO ACTION ? From the doc they seem exactly the same. Is this the case? If so, why have both? From MySQL Documentation: https://dev.mysql.com/doc/refman/8.0/en/create-table-foreign-keys.html Some database systems have deferred checks, and NO ACTION is a deferred check. In MySQL, foreign key constraints are checked immediately, so NO ACTION is the same as RESTRICT . They are identical in MySQL. In the SQL 2003 standard there are 5 different referential actions: CASCADE RESTRICT NO ACTION SET NULL SET DEFAULT The difference between NO

I have a couple of models: class Customer(models.Model): customer_name = models.CharField(max_length=200) def __unicode__(self): return self.customer_name class Meta: ordering = ('customer_name',) class Unit(models.Model): unit_number = models.IntegerField() rentable = models.BooleanField() owner = models.ForeignKey(Customer, related_name='units', blank=True, null=True) def __unicode__(self): return str(self.unit_number) class Meta: ordering = ('unit_number',) I have the admin interface working fine when I'm adding a unit (I can select which customer to assign it to) but when I go to create

Ok. So I know what a primary key in DB is. If you have a table in a database, a primary key is a single value that is unique to each row in your table. For example: id | name | whatever ------------------------- 1 Alice .... 2 Bob .... 45 Eve .... 988 .... .... So I need a good, simple example to explain what exactly a foreign key is. Because I just don't get it :) Edit: OK it's pretty easy, I guess I was over-complicating the problem. So one final question, the only restriction on foreign keys is that it they are a valid primary key value in the table I am referring to? A foreign key is a