Prepare Notebook

To run this code, written at the very end of Chapter 3, you need a working empty database.

To move the project into a valid state, please use the command git chapter [chapter-number] to find a valid commit. A commit at the end of Chapter 3, or any commit in Chapters 4-9, should work just fine. Use git checkout [commit] to change the state of the project. Once there, delete the database (if it exists).

$ rm db.sqlite3

To (re-)create the database:

$ ./manage.py migrate

Please see the Read Me file or the actual book for more details.



In [1]:

    
from datetime import date
from organizer.models import Tag, Startup, NewsLink
from blog.models import Post

Interacting With the Database



In [2]:

    
edut = Tag(name='Education', slug='education')



In [3]:

    
edut









    Out[3]:





<Tag: Education>



In [4]:

    
edut.save()



In [5]:

    
edut.delete()



In [6]:

    
edut  # still in memory!









    Out[6]:





<Tag: Education>

Creation and Destruction with Managers



In [7]:

    
type(Tag.objects)  # a model manager









    Out[7]:





django.db.models.manager.Manager



In [8]:

    
Tag.objects.create(name='Video Games', slug='video-games')









    Out[8]:





<Tag: Video Games>



In [9]:

    
# create multiple objects in a go!
Tag.objects.bulk_create([
    Tag(name='Django', slug='django'),
    Tag(name='Mobile', slug='mobile'),
    Tag(name='Web', slug='web'),
])









    Out[9]:





[<Tag: Django>, <Tag: Mobile>, <Tag: Web>]



In [10]:

    
Tag.objects.all()









    Out[10]:





[<Tag: Django>, <Tag: Mobile>, <Tag: Video Games>, <Tag: Web>]



In [11]:

    
Tag.objects.all()[0]  # acts like a list









    Out[11]:





<Tag: Django>



In [12]:

    
type(Tag.objects.all())  # is not a list









    Out[12]:





django.db.models.query.QuerySet



In [13]:

    
# managers are not accessible to model instances, only to model classes!
try:
    edut.objects
except AttributeError as e:
    print(e)









    



Manager isn't accessible via Tag instances

Methods of Data Retrieval



In [14]:

    
Tag.objects.all()









    Out[14]:





[<Tag: Django>, <Tag: Mobile>, <Tag: Video Games>, <Tag: Web>]



In [15]:

    
Tag.objects.count()









    Out[15]:





4

The `get` method



In [16]:

    
Tag.objects.get(slug='django')









    Out[16]:





<Tag: Django>



In [17]:

    
type(Tag.objects.all())









    Out[17]:





django.db.models.query.QuerySet



In [18]:

    
type(Tag.objects.get(slug='django'))









    Out[18]:





organizer.models.Tag



In [19]:

    
# case-sensitive!
try:
    Tag.objects.get(slug='Django')
except Tag.DoesNotExist as e:
    print(e)









    



Tag matching query does not exist.



In [20]:

    
# the i is for case-Insensitive
Tag.objects.get(slug__iexact='DJANGO')









    Out[20]:





<Tag: Django>



In [21]:

    
Tag.objects.get(slug__istartswith='DJ')









    Out[21]:





<Tag: Django>



In [22]:

    
Tag.objects.get(slug__contains='an')









    Out[22]:





<Tag: Django>



In [23]:

    
# get always returns a single object
try:
    # djangO, mObile, videO-games
    Tag.objects.get(slug__contains='o')
except Tag.MultipleObjectsReturned as e:
    print(e)









    



get() returned more than one Tag -- it returned 3!

The `filter` method



In [24]:

    
## unlike get, can fetch multiple objects
Tag.objects.filter(slug__contains='o')









    Out[24]:





[<Tag: Django>, <Tag: Mobile>, <Tag: Video Games>]



In [25]:

    
type(Tag.objects.filter(slug__contains='o'))









    Out[25]:





django.db.models.query.QuerySet

Chaining Calls



In [26]:

    
Tag.objects.filter(slug__contains='o').order_by('-name')









    Out[26]:





[<Tag: Video Games>, <Tag: Mobile>, <Tag: Django>]



In [27]:

    
# first we call order_by on the manager
Tag.objects.order_by('-name')









    Out[27]:





[<Tag: Web>, <Tag: Video Games>, <Tag: Mobile>, <Tag: Django>]



In [28]:

    
# now we call filter on the manager, and order the resulting queryset
Tag.objects.filter(slug__contains='e').order_by('-name')









    Out[28]:





[<Tag: Web>, <Tag: Video Games>, <Tag: Mobile>]

`values` and `values_list`



In [29]:

    
Tag.objects.values_list()









    Out[29]:





[(3, 'Django', 'django'), (4, 'Mobile', 'mobile'), (2, 'Video Games', 'video-games'), (5, 'Web', 'web')]



In [30]:

    
type(Tag.objects.values_list())









    Out[30]:





django.db.models.query.ValuesListQuerySet



In [31]:

    
Tag.objects.values_list('name', 'slug')









    Out[31]:





[('Django', 'django'), ('Mobile', 'mobile'), ('Video Games', 'video-games'), ('Web', 'web')]



In [32]:

    
Tag.objects.values_list('name')









    Out[32]:





[('Django',), ('Mobile',), ('Video Games',), ('Web',)]



In [33]:

    
Tag.objects.values_list('name', flat=True)









    Out[33]:





['Django', 'Mobile', 'Video Games', 'Web']



In [34]:

    
type(Tag.objects.values_list('name', flat=True))









    Out[34]:





django.db.models.query.ValuesListQuerySet

Data in Memory vs Data in the Database



In [35]:

    
jb = Startup.objects.create(
    name='JamBon Software',
    slug='jambon-software',
    contact='django@jambonsw.com',
    description='Web and Mobile Consulting.\n'
                'Django Tutoring.\n',
    founded_date=date(2013, 1, 18),
    website='https://jambonsw.com/',
)
jb  # this output only clear because of __str__()









    Out[35]:





<Startup: JamBon Software>



In [36]:

    
jb.founded_date









    Out[36]:





datetime.date(2013, 1, 18)



In [37]:

    
jb.founded_date = date(2014,1,1)
# we're not calling save() !
jb.founded_date









    Out[37]:





datetime.date(2014, 1, 1)



In [38]:

    
# get version in database
jb = Startup.objects.get(slug='jambon-software')
# work above is all for nought because we didn't save()
jb.founded_date









    Out[38]:





datetime.date(2013, 1, 18)

Connecting Data through Relations



In [39]:

    
djt = Post.objects.create(
    title='Django Training',
    slug='django-training',
    text=(
        "Learn Django in a classroom setting "
        "with JamBon Software."),
)
djt









    Out[39]:





<Post: Django Training on 2015-06-09>



In [40]:

    
djt.pub_date = date(2013, 1, 18)
djt.save()
djt









    Out[40]:





<Post: Django Training on 2013-01-18>



In [41]:

    
type(djt.tags)









    Out[41]:





django.db.models.fields.related.create_many_related_manager.<locals>.ManyRelatedManager



In [42]:

    
type(djt.startups)









    Out[42]:





django.db.models.fields.related.create_many_related_manager.<locals>.ManyRelatedManager



In [43]:

    
djt.tags.all()









    Out[43]:





[]



In [44]:

    
djt.startups.all()









    Out[44]:





[]



In [45]:

    
django = Tag.objects.get(slug__contains='django')
djt.tags.add(django)
djt.tags.all()









    Out[45]:





[<Tag: Django>]



In [46]:

    
django.blog_posts.all()  # a "reverse" relation









    Out[46]:





[<Post: Django Training on 2013-01-18>]



In [47]:

    
django.startup_set.add(jb)  # a "reverse" relation
django.startup_set.all()









    Out[47]:





[<Startup: JamBon Software>]



In [48]:

    
jb.tags.all()  # the "forward" relation









    Out[48]:





[<Tag: Django>]



In [49]:

    
# on more time, for repetition!
djt









    Out[49]:





<Post: Django Training on 2013-01-18>



In [50]:

    
# "forward" relation
djt.startups.add(jb)
djt.startups.all()









    Out[50]:





[<Startup: JamBon Software>]



In [51]:

    
jb.blog_posts.all()  # "reverse" relation









    Out[51]:





[<Post: Django Training on 2013-01-18>]