Generics in Django

Question

Could someone translate this Java Pseudo code with generics to Django models? I don't understand the content type concept. It would also be possible to leave out the map and just have a list of KeyValuePairs or KeyValueExamples.

class Dictionary<T extends KeyValuePair>

class KeyValuePair
    String key
    String value

class KeyValueExample extends KeyValuePair
    String example

class Container
    Dictionary<KeyValuePair> itemsOne
    Dictionary<KeyValueExample> itemsTwo

Answer 1

Django's contenttypes doesn't have anything common with generics from Java. Python has a dynamic type system so there is no need for generics.

This means that you can put any object of any class into the dictionary:

class Container(object):

    def __init__(self):
        self.itemsOne = {}
        self.itemsTwo = {}

container = Container()
container.itemsOne['123'] = '123'
container.itemsOne[321] = 321
container.itemsTwo[(1,2,3)] = "tuple can be a key"

If you want to implement your classes in django models then code could be something like this:

class KeyValuePairBase(models.Model):    
    key = models.CharField(max_length=30)
    value = models.CharField(max_length=30)    
    class Meta:
        abstract = True    

class KeyValuePair(KeyValuePairBase):
    pass    

class KeyValueExample(KeyValuePairBase):
    example = models.CharField(max_length=30)    

class Container(models.Model):    
    items_one = models.ManyToManyField(KeyValuePair)
    items_two = models.ManyToManyField(KeyValueExample)

# usage of these models

kvp = KeyValuePair.objects.create(key='key', value='value')
kve = KeyValueExample.objects.create(key='key', value='value',
                                     example='Example text')

container = Container.objects.create()
container.items_one.add(kvp)
container.items_two.add(kve)