Many to Many relation which has either not been installed or is abstract

Question

Consider the following (simplified) Django Models:

class productFamily(models.Model):
    name = models.CharField(max_length = 256)
    text = models.TextField(blank = False)
    image = models.ImageField(upload_to="products/img/")
    def __unicode__(self):
        return self.name

class productModel(models.Model):
    productFamily = models.ForeignKey('productFamily')
    productFamily.help_text = 'ProductFamily to which this model belongs.'
    artNumber = models.CharField(max_length=100)
    name = models.CharField(max_length = 256)
    productDownloads = models.ManyToManyField('productModelDownLoad')
    productDownloads.help_text = 'Files associated to this product Model.'
    def __unicode__(self):
        return self.name

class productModelDownload(models.Model):
    file = models.FileField(upload_to="products/downloads/")
    def __unicode__(self):
        return str(self.file)

I get the following error:

products.productmodel: 'productDownloads' has an m2m relation with model productModelDownLoad, which has either not been installed or is abstract.

I found a page in the django docs that seems to address this, but i can't quite make sense of what it means: http://www.djangoproject.com/documentation/models/invalid_models/

The Model looks valid to me, so what is the problem here?

Answer 1

You have to place the class productModelDownload before the productModel class. They are processed from top to down while validating the models.

Answer 2

models.ManyToManyField('productModelDownLoad') - 'Load' is uppercased

class productModelDownload(models.Model): - 'load' is in lower case

Answer 3

Interestingly there are two ways to solve this:
a) Thomas's answer does the trick,
b) But, so does Mike Korobov's:
There is a stray capital letter in the field name in the relation:

productDownloads = models.ManyToManyField('productModelDown*L*oad')

Correcting this stray capital also resolves this issue.