How to update DjangoItem in Scrapy

Question

I\'ve been working with Scrapy but run into a bit of a problem.

DjangoItem has a save method to persist items using the Django ORM. This is

Answer 1

Unfortunately, the best way that I found to accomplish this is to do exactly what was stated: Check if the item exists in the database using django_model.objects.get, then update it if it does.

In my settings file, I added the new pipeline:

ITEM_PIPELINES = {
    # ...
    # Last pipeline, because further changes won't be saved.
    'apps.scrapy.pipelines.ItemPersistencePipeline': 999
}

I created some helper methods to handle the work of creating the item model, and creating a new one if necessary:

def item_to_model(item):
    model_class = getattr(item, 'django_model')
    if not model_class:
        raise TypeError("Item is not a `DjangoItem` or is misconfigured")

    return item.instance


def get_or_create(model):
    model_class = type(model)
    created = False

    # Normally, we would use `get_or_create`. However, `get_or_create` would
    # match all properties of an object (i.e. create a new object
    # anytime it changed) rather than update an existing object.
    #
    # Instead, we do the two steps separately
    try:
        # We have no unique identifier at the moment; use the name for now.
        obj = model_class.objects.get(name=model.name)
    except model_class.DoesNotExist:
        created = True
        obj = model  # DjangoItem created a model for us.

    return (obj, created)


def update_model(destination, source, commit=True):
    pk = destination.pk

    source_dict = model_to_dict(source)
    for (key, value) in source_dict.items():
        setattr(destination, key, value)

    setattr(destination, 'pk', pk)

    if commit:
        destination.save()

    return destination

Then, the final pipeline is fairly straightforward:

class ItemPersistencePipeline(object):
    def process_item(self, item, spider):
        try:
             item_model = item_to_model(item)
        except TypeError:
            return item

        model, created = get_or_create(item_model)

        update_model(model, item_model)

        return item

Answer 2

for related models with foreignkeys

def update_model(destination, source, commit=True):
    pk = destination.pk

    source_fields = fields_for_model(source)
    for key in source_fields.keys():
        setattr(destination, key, getattr(source, key))

    setattr(destination, 'pk', pk)

    if commit:
        destination.save()

    return destination

Answer 3

I think it could be done more simply with

class DjangoSavePipeline(object):
    def process_item(self, item, spider):
        try:
            product = Product.objects.get(myunique_id=item['myunique_id'])
            # Already exists, just update it
            instance = item.save(commit=False)
            instance.pk = product.pk
        except Product.DoesNotExist:
            pass
        item.save()
        return item

Assuming your django model has some unique id from the scraped data, such as a product id, and here assuming your Django model is called Product.