DjangoItem is a class of item that gets its fields definition from a Django model, you simply create a DjangoItem and specify what Django model it relates to.
Besides of getting the model fields defined on your item, DjangoItem provides a method to create and populate a Django model instance with the item data.
DjangoItem works much like ModelForms in Django, you create a subclass and define its django_model attribute to be a valid Django model. With this you will get an item with a field for each Django model field.
In addition, you can define fields that aren’t present in the model and even override fields that are present in the model defining them in the item.
Let’s see some examples:
Creating a Django model for the examples:
from django.db import models class Person(models.Model): name = models.CharField(max_length=255) age = models.IntegerField()
Defining a basic DjangoItem:
from scrapy.contrib.djangoitem import DjangoItem class PersonItem(DjangoItem): django_model = Person
DjangoItem work just like Item:
>>> p = PersonItem() >>> p['name'] = 'John' >>> p['age'] = '22'
To obtain the Django model from the item, we call the extra method save() of the DjangoItem:
>>> person = p.save() >>> person.name 'John' >>> person.age '22' >>> person.id 1
The model is already saved when we call save(), we can prevent this by calling it with commit=False. We can use commit=False in save() method to obtain an unsaved model:
>>> person = p.save(commit=False) >>> person.name 'John' >>> person.age '22' >>> person.id None
As said before, we can add other fields to the item:
class PersonItem(DjangoItem): django_model = Person sex = Field()
>>> p = PersonItem() >>> p['name'] = 'John' >>> p['age'] = '22' >>> p['sex'] = 'M'
fields added to the item won’t be taken into account when doing a save()
And we can override the fields of the model with your own:
class PersonItem(DjangoItem): django_model = Person name = Field(default='No Name')
This is useful to provide properties to the field, like a default or any other property that your project uses.
DjangoItem is a rather convenient way to integrate Scrapy projects with Django models, but bear in mind that Django ORM may not scale well if you scrape a lot of items (ie. millions) with Scrapy. This is because a relational backend is often not a good choice for a write intensive application (such as a web crawler), specially if the database is highly normalized and with many indices.
Django settings set up¶
To use the Django models outside the Django application you need to set up the DJANGO_SETTINGS_MODULE environment variable and –in most cases– modify the PYTHONPATH environment variable to be able to import the settings module.
There are many ways to do this depending on your use case and preferences. Below is detailed one of the simplest ways to do it.
Suppose your Django project is named mysite, is located in the path /home/projects/mysite and you have created an app myapp with the model Person. That means your directory structure is something like this:
/home/projects/mysite ├── manage.py ├── myapp │ ├── __init__.py │ ├── models.py │ ├── tests.py │ └── views.py └── mysite ├── __init__.py ├── settings.py ├── urls.py └── wsgi.py
Then you need to add /home/projects/mysite to the PYTHONPATH environment variable and set up the environment variable DJANGO_SETTINGS_MODULE to mysite.settings. That can be done in your Scrapy’s settings file by adding the lines below:
import sys sys.path.append('/home/projects/mysite') import os os.environ['DJANGO_SETTINGS_MODULE'] = 'mysite.settings'
Notice that we modify the sys.path variable instead the PYTHONPATH environment variable as we are already within the python runtime. If everything is right, you should be able to start the scrapy shell command and import the model Person (i.e. from myapp.models import Person).