1

I have the following Model: 

class Car(models.Model):
 id = models.AutoField(primary_key=True)
 slug = models.CharField(max_length=128L, unique=True, blank=True)
 name = models.CharField(max_length=128L, blank=True)
 model_slug = models.CharField(max_length=128L, unique=True, blank=True)
 ...

Whenever I'm getting a list of Car from an XML file, some of them show up multiple times
(with the same slug), if I try to save that, I get
IntegrityError(1062, "Duplicate entry 'car-slug' for key 'slug'")

I want it to load the existing Car (or updated it, whichever is easier) in case there's a Duplicate error.
But I want it to be generic enough so that it would work for model_slug (or any unique field that generates that error).

4

3 回答 3

2

You need get_or_create:

car,created = Car.objects.get_or_create(slug='car-slug')
if created:
   print 'New car was created'
   car.slug = 'new-car-slug'
else:
   # do whatever needs to be done here
   # with the existing car object, which will
   # be car
   # car.name = 'new name'

car.save()

Whatever arguments you provide to get_or_create, it will use those to search existing records for the model.

Suppose you don't know what combination of fields will trigger a duplicate. The easy way is to find out which fields in your model have that restriction (ie unique=True). You can introspect this information from your model, or a simpler way is to simply pass these fields to get_or_create.

First step is to create a mapping between your XML fields and your model's fields:

xml_lookup = {}
xml_lookup = {'CAR-SLUG': 'slug'}  # etc. etc.

You can populate this will all fields if you want, but my suggestion is to populate it only with those fields that have a unique constraint on them.

Next, while you are parsing your XML, populate a dictionary for each record, mapping each field:

for row in xml_file:
    lookup_dict = {}
    lookup_dict[xml_lookup[row['tag']] = row['value']  # Or something similar
    car, created = Car.objects.get_or_create(**lookup_dict)
    if created:
       # Nothing matched, a new record was created
       # Any any logic you need here
    else:
       # Existing record matched the search parameters
       # Change/update whatever field to prevent the IntegrityError
       car.model_slug = row['MODEL_SLUG']
       # Set/update fields as required
    car.save()  # Save the modified object
于 2013-05-26T09:37:26.800 回答
0

you can filter the duplicates car entries in memory first and then invoke create on new items, e.g,

uniq_attrs = ['slug', 'model_slug', ...]
existed_attrs = set()
for car in car_list:
    # skip the duplicates
    if any([(attr, car[attr]) in existed_attrs for attr in uniq_attrs):
        continue
    uniq_attrs.update([(attr, car[attr]) for attr in uniq_attrs])

    # save the new car to db
    Car.objects.save(....)

or you can try get_or_create on unique fields and then save other attribues with model save, e.g.,

for car in car_list:
    attr_dict = {attr:car[attr] for attr in uniq_attrs}
    car, created = Car.objects.get_or_create(**attr_dict)

    # already created before
    if created:
        continue

    # save other attributes
    car.set(...)
    car.set(...)
    car.save()
于 2013-05-26T12:04:23.603 回答
0

I ended up writing a custom save on the model (so that my code doesn't change, just the model):

def save(self, *args, **kwargs):
    try:
        super(Car, self).save(*args, **kwargs)
    except IntegrityError, e:
        existing_object = Car.objects.get(slug=self.slug)
        self = existing_object
        super(Car, self).save(*args, **kwargs)
        return existing_object.id

Now I return the object's ID to assign it so the save() command looks like this:

the_id = generic_object.save() #e.g. Car
if the_id:
    generic_object.id = the_id
于 2013-05-31T07:32:54.830 回答