Django ORM Operations Database Common API

Last night, we completed a simple example to manipulate a database table. Today, we need to familiarize ourselves with more APIs for more complex functions. This step is complete, and we don't have much of a problem with small data operations.

Now, let's take a look at the Django official documentation to learn

1. Construct the data table

Copy the following to your friend charm, then execute the Migrate command

Class Blog (models. Model):
Name = models. Charfield (max_length=100)
Tagline = models. TextField ()

def __str__ (self): # __unicode__ on Python 2
Return Self.name

Class Author (models. Model):
Name = models. Charfield (max_length=200)
email = models. Emailfield ()

def __str__ (self): # __unicode__ on Python 2
Return Self.name

Class Entry (models. Model):
Blog = models. ForeignKey (Blog)
Headline = models. Charfield (max_length=255)
Body_text = models. TextField ()
Pub_date = models. Datefield ()
Mod_date = models. Datefield ()
Authors = models. Manytomanyfield (Author)
N_comments = models. Integerfield ()
N_pingbacks = models. Integerfield ()
Rating = models. Integerfield ()

def __str__ (self): # __unicode__ on Python 2
Return Self.headline

2. Create an Object
b = Blog (name= ' Beatles blog ', tagline= ' all the latest Beatles news. ')

B.save ()

So we're going to put the data in.

The same object, which is saved and then re-assigned, will perform the modify operation

3. Save ForeignKey and Manytomanyfield fields

Now that our data has been saved, and we have established an association

In model, entry is associated with a foreign key blog (ForeignKey)

So when you create a entry, you need to get a blog object, assign a value to entry, and then perform the operation of saving the database.

Entry = entry (headline= ' test123 ', body_text= ' test123 ', Pub_date=datetime.datetime.now (),
Mod_date=datetime.datetime.now (), n_comments=123, n_pingbacks=456, rating=789)

Cheese_blog = Blog.objects.get (name= "Beatles blog")

Entry.blog = Cheese_blog
Entry.save ()

Now, dealing with the manytomanyfield situation.

It has to be taken out:

data = Entry.authors.iterator ()

Direct access to attributes and turn the query set into an iterative

4. Querying objects

All_entries = Entry.objects.all ()

5. Search by condition

Filter (**kwargs) returns a new match query parameter after the Queryset

Exclude (**kwargs) returns a new unmatched query parameter after the Queryset

Entry.objects.filter (pub_date__year=2006)

Q2 = Q1.exclude (Pub_date__gte=datetime.date.today ())

6. Link Query

Entry.objects.filter (headline__startswith= ' what ')
. Exclude (Pub_date__gte=datetime.now ())
. Filter (Pub_date__gte=datetime (2005, 1, 1))

7. Deferred Query

Creating querysets does not touch the database operation, you can merge multiple filters together until Django starts querying when the value is evaluated

Q = Entry.objects.filter (headline__startswith= "what")
Q = Q.filter (Pub_date__lte=datetime.now ())
Q = q.exclude (body_text__icontains= "food")

8. Retrieving a single object

One_entry = Entry.objects.get (pk=1)

9. Restricted query: Paging/sorting query

Entry.objects.all () [: 5]

Entry.objects.order_by (' headline ') [0:1].get ()

10. Field Query

Entry.objects.filter (pub_date__lte= ' 2006-01-01 ')

Convert to SQL:

SELECT * from Blog_entry WHERE pub_date <= ' 2006-01-01 ';

11.exact

Entry.objects.get (headline__exact= "Man Bites Dog")

Convert to SQL:

SELECT ... WHERE headline = ' Man Bites dog ';

12.iexact--ignoring case

Blog.objects.get (name__iexact= "Beatles Blog")

13.contains--contains queries, case sensitive

Entry.objects.get (headline__contains= ' Lennon ')

Convert to SQL:

SELECT ... WHERE headline like '%lennon% ';

Icontains Case insensitive

Startswith,endswith,istartswith,iendswith

Fuzzy query before and after

14. Connection Query

Query Blog__name match, return entry

Entry.objects.filter (blog__name__exact= ' Beatles blog ')

Query Entry__headline match, return blog

Blog.objects.filter (entry__headline__contains= ' Lennon ')

If the intermediate model does not have a value across a multi-tier relational query, Django treats it as null without exception

Blog.objects.filter (entry__author__name= ' Lennon ');
Blog.objects.filter (entry__author__name__isnull=true);
Blog.objects.filter (
Entry__author__isnull=false,
Entry__author__name__isnull=true);

A 15.F object that operates on a field. Just like in SQL, column a +b column. F objects are seldom used

From Django.db.models import F
Entry.objects.filter (n_pingbacks__lt=f (' n_comments '))

Column subtraction All can

Entry.objects.filter (n_pingbacks__lt=f (' n_comments ') * 2)
Entry.objects.filter (rating__lt=f (' n_comments ') + F (' n_pingbacks '))
Entry.objects.filter (author__name=f (' Blog__name '))

16.like statement Escape percent sign

Entry.objects.filter (headline__contains= '% ')

Escaped as:

SELECT ... WHERE headline like '%\%% ';

17. Delete

Q = Entry.objects.filter (headline__startswith= "what")

Q.delete ()

18. Batch Modification

Entry.objects.filter (pub_date__year=2007). Update (headline= ' Everything is the same ')

One-time modification of all entry blog Properties point to

b = Blog.objects.get (pk=1)

Entry.objects.all (). Update (BLOG=B)

Update can also use the F ()

Entry.objects.update (headline=f (' Blog__name '))

19.one-to-many relationship

E = Entry.objects.get (id=2)
Print E.blog # Hits The database to retrieve the associated blog

E = Entry.objects.select_related (). Get (id=2)
Print E.blog # is not being taken to the database; Use the values in the cache.

b = Blog.objects.get (id=1)
B.entry_set.all () # Returns the associated object for all blogs.

# B.entry_set is a Manager that returns querysets.
B.entry_set.filter (headline__contains= ' Lennon ')
B.entry_set.count ()

b = Blog.objects.get (id=1)
B.entries.all () # Returns the associated object for all blogs

# b.entries is a Manager that returns querysets.
B.entries.filter (headline__contains= ' Lennon ')
B.entries.count ()

Add (Obj1, Obj2, ...) make connections to multiple objects

Create (**kwargs) Create new Object

Remove (obj1, obj2, ...) Remove multiple relationship objects

Clear () Cleans up all relationship objects

20.many-to-many relationship

E = Entry.objects.get (id=3)
E.authors.all () # Return entry all authors
E.authors.count ()
E.authors.filter (name__contains= ' John ')

A = Author.objects.get (id=5)
A.entry_set.all () # Return author all entry

21.one-to-one relationship

To set when defining a model

Class Entrydetail (models. Model):
Entry = models. Onetoonefield (Entry)
Details = models. TextField ()

ed = EntryDetail.objects.get (id=2)
Ed.entry # Returns the entry object.

Django ORM Operations Database Common API