Modifying entry in django admin creates duplicate - mysql

Question

I am using the django admin to modify records in a table. The problem is that whenever I modify an entry, when I click save, instead of modifying that entry, the old one is not modified and a new entry containing the modified details is being added.
For example, if I have the following:
Aardvark | Orycteropus | Some description | aardvark | animals/images/aardvark.jpg
when I change the first field to Aardvarkon, I get the following:
Aardvark | Orycteropus | Some description | aardvark | animals/images/aardvark.jpg
Aardvarkon | Orycteropus | Some description | aardvark | animals/images/aardvark.jpg
I have the following django model:
def article_file_name(instance, filename):
return ANIMAL_IMAGES_BASE_DIR[1:] + instance.ai_species_species_sanitized + '.jpg'
class ai_species(models.Model):
ai_species_species = models.CharField('Species', max_length=100, primary_key=True, db_column='species')
ai_species_genus = models.ForeignKey(ai_genera, max_length=50, blank=False, null=False, db_column='genus')
ai_species_description = models.CharField('Description', max_length=65000, db_column='description')
ai_species_species_sanitized = models.CharField(max_length=100, blank=False, null=False, db_column='species_sanitized')
image_url = models.ImageField(max_length=100, storage=OverwriteStorage(), validators=[validate_jpg_extension], upload_to=article_file_name)
class Meta:
db_table = 'Species'
verbose_name = 'Animal species'
verbose_name_plural = 'Animal species'
def __unicode__(self): # Required, don't remove.
return self.ai_species_species
And the following helpers:
def validate_jpg_extension(value):
if not value.name.lower().endswith('.jpg') and not value.name.lower().endswith('.jpeg'):
raise ValidationError(u'Invalid file format! Only jpg or jpeg files allowed!')
class OverwriteStorage(FileSystemStorage):
def get_available_name(self, name):
# If the filename already exists, remove it.
if self.exists(name):
os.remove(os.path.join(settings.MEDIA_ROOT, name))
return name
This is the MySQL table schema for this table:
This is a very counter-intuitive behavior and I haven't found any other occurrences of this online. Any help on this would be greatly appreciated.

Answer 1

Here's the culprit:
ai_species_species = models.CharField('Species', max_length=100, primary_key=True, db_column='species')
Since you've defined the species as the primary key, any time you change this field in the admin it will create a new record (because there isn't already a record with that primary key).
FYI, primary keys aren't supposed to be things that change for a given record, since changing the primary key will invalidate every foreign key (ForeignKey, OneToOneField, and ManyToManyField) that refers to the record.
BTW, you don't need to be prefixing the field names with ai_species_; it's cluttering. Removing those prefixes would remove the need for the db_column parameters as well.