django-2

本節內容

學員管理系統練習

Django ORM操做進階

用戶認證

 

 

 

 

Django練習小項目：學員管理系統設計開發

帶着項目需求學習是最有趣和效率最高的，今天就來基於下面的需求來繼續學習Django 

項目需求：

1.分講師\學員\課程顧問角色,
2.學員能夠屬於多個班級,學員成績按課程分別統計
3.每一個班級至少包含一個或多個講師
4.一個學員要有狀態轉化的過程 ,好比未報名前,報名後,畢業老學員
5.客戶要有諮詢紀錄, 後續的按期跟蹤紀錄也要保存
6.每一個學員的全部上課出勤狀況\學習成績都要保存
7.學校能夠有分校區,默認每一個校區的員工只能查看和管理本身校區的學員
8.客戶諮詢要區分來源

  學員管理系統表結構

 

經常使用ORM操做

  示例models

建立

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>>>  from  blog.models  import  Blog >>> b  =  Blog(name = 'Beatles Blog' , tagline = 'All the latest Beatles news.' ) >>> b.save()

This performs an INSERT SQL statement behind the scenes. Django doesn’t hit the database until you explicitly call save().

The save() method has no return value.

處理帶外鍵關聯或多對多關聯的對象 

 

ForeignKey的關聯

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>>>  from  blog.models  import  Entry >>> entry  =  Entry.objects.get(pk = 1 ) >>> cheese_blog  =  Blog.objects.get(name = "Cheddar Talk" ) >>> entry.blog  =  cheese_blog >>> entry.save()

ManyToManyField關聯　　

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>>>  from  blog.models  import  Author >>> joe  =  Author.objects.create(name = "Joe" ) >>> entry.authors.add(joe)

添加多個ManyToMany對象

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>>> john  =  Author.objects.create(name = "John" ) >>> paul  =  Author.objects.create(name = "Paul" ) >>> george  =  Author.objects.create(name = "George" ) >>> ringo  =  Author.objects.create(name = "Ringo" ) >>> entry.authors.add(john, paul, george, ringo)

 

查詢

 1 all_entries = Entry.objects.all() #查詢全部
 2 Entry.objects.filter(pub_date__year=2006) #查詢全部pub_date爲2006年的紀錄
 3 Entry.objects.all().filter(pub_date__year=2006) #與上面那句同樣
 4 >>> Entry.objects.filter(   #鏈式查詢
 5 ...     headline__startswith='What'
 6 ... ).exclude(
 7 ...     pub_date__gte=datetime.date.today()
 8 ... ).filter(
 9 ...     pub_date__gte=datetime(2005, 1, 30)
10 ... )
11 
12 one_entry = Entry.objects.get(pk=1) #單條查詢
13 
14 Entry.objects.all()[:5] #查詢前5條
15 Entry.objects.all()[5:10] #你猜
16 
17 Entry.objects.order_by('headline')[0] #按headline排序取第一條
18 
19 Entry.objects.filter(pub_date__lte='2006-01-01') #至關於sql語句SELECT * FROM blog_entry WHERE pub_date <= '2006-01-01';
20 
21 Entry.objects.get(headline__exact="Cat bites dog") #至關於SELECT ... WHERE headline = 'Cat bites dog';
22 Blog.objects.get(name__iexact="beatles blog") #與上面相同,只是大小寫不敏感
23 
24 Entry.objects.get(headline__contains='Lennon') #至關 於SELECT ... WHERE headline LIKE '%Lennon%';

#This example retrieves all Entry objects with a Blog whose name is 'Beatles Blog':
Entry.objects.filter(blog__name='Beatles Blog')

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

對同一表內不一樣的字段進行對比查詢，In the examples given so far, we have constructed filters that compare the value of a model field with a constant. But what if you want to compare the value of a model field with another field on the same model?

Django provides F expressions to allow such comparisons. Instances of F() act as a reference to a model field within a query. These references can then be used in query filters to compare the values of two different fields on the same model instance.

For example, to find a list of all blog entries that have had more comments than pingbacks, we construct an F() object to reference the pingback count, and use that F() object in the query:

1 2	>>>  from  django.db.models  import  F >>> Entry.objects. filter (n_comments__gt = F( 'n_pingbacks' ))

Django supports the use of addition, subtraction, multiplication, division, modulo, and power arithmetic with F() objects, both with constants and with other F() objects. To find all the blog entries with more than twice as many comments as pingbacks, we modify the query:

1	>>> Entry.objects. filter (n_comments__gt = F( 'n_pingbacks' )  *  2 )

To find all the entries where the rating of the entry is less than the sum of the pingback count and comment count, we would issue the query:

1	>>> Entry.objects. filter (rating__lt = F( 'n_comments' )  +  F( 'n_pingbacks' ))

For date and date/time fields, you can add or subtract a timedelta object. The following would return all entries that were modified more than 3 days after they were published:

1 2	>>>  from  datetime  import  timedelta >>> Entry.objects. filter (mod_date__gt = F( 'pub_date' )  +  timedelta(days = 3 ))

Caching and QuerySets

Each QuerySet contains a cache to minimize database access. Understanding how it works will allow you to write the most efficient code.

In a newly created QuerySet, the cache is empty. The first time a QuerySet is evaluated – and, hence, a database query happens – Django saves the query results in the QuerySet’s cache and returns the results that have been explicitly requested (e.g., the next element, if the QuerySet is being iterated over). Subsequent evaluations of the QuerySet reuse the cached results.

Keep this caching behavior in mind, because it may bite you if you don’t use your QuerySets correctly. For example, the following will create two QuerySets, evaluate them, and throw them away:

1 2	>>>  print ([e.headline  for  e  in  Entry.objects. all ()]) >>>  print ([e.pub_date  for  e  in  Entry.objects. all ()])

That means the same database query will be executed twice, effectively doubling your database load. Also, there’s a possibility the two lists may not include the same database records, because an Entry may have been added or deleted in the split second between the two requests.

To avoid this problem, simply save the QuerySet and reuse it:

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>>> queryset  =  Entry.objects. all () >>>  print ([p.headline  for  p  in  queryset])  # Evaluate the query set. >>>  print ([p.pub_date  for  p  in  queryset])  # Re-use the cache from the evaluation.

When QuerySets are not cached¶

Querysets do not always cache their results. When evaluating only part of the queryset, the cache is checked, but if it is not populated then the items returned by the subsequent query are not cached. Specifically, this means that limiting the querysetusing an array slice or an index will not populate the cache.

For example, repeatedly getting a certain index in a queryset object will query the database each time:

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>>> queryset  =  Entry.objects. all () >>>  print  queryset[ 5 ]  # Queries the database >>>  print  queryset[ 5 ]  # Queries the database again

However, if the entire queryset has already been evaluated, the cache will be checked instead:

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>>> queryset  =  Entry.objects. all () >>> [entry  for  entry  in  queryset]  # Queries the database >>>  print  queryset[ 5 ]  # Uses cache >>>  print  queryset[ 5 ]  # Uses cache

 

Complex lookups with Q objects（複雜查詢）

Keyword argument queries – in filter(), etc. – are 「AND」ed together. If you need to execute more complex queries (for example, queries with OR statements), you can use Q objects.

A Q object (django.db.models.Q) is an object used to encapsulate a collection of keyword arguments. These keyword arguments are specified as in 「Field lookups」 above.

For example, this Q object encapsulates a single LIKE query:

1 2	from  django.db.models  import  Q Q(question__startswith = 'What' )

Q objects can be combined using the & and | operators. When an operator is used on two Q objects, it yields a new Q object.

For example, this statement yields a single Q object that represents the 「OR」 of two "question__startswith" queries:

1	Q(question__startswith = 'Who' ) | Q(question__startswith = 'What' )

This is equivalent to the following SQL WHERE clause:

1	WHERE  question  LIKE  'Who%'  OR  question  LIKE  'What%'

You can compose statements of arbitrary complexity by combining Q objects with the & and | operators and use parenthetical grouping. Also, Q objects can be negated using the ~ operator, allowing for combined lookups that combine both a normal query and a negated (NOT) query:

1	Q(question__startswith = 'Who' ) | ~Q(pub_date__year = 2005 )

Each lookup function that takes keyword-arguments (e.g. filter(), exclude(), get()) can also be passed one or more Qobjects as positional (not-named) arguments. If you provide multiple Q object arguments to a lookup function, the arguments will be 「AND」ed together. For example:

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Poll.objects.get(      Q(question__startswith = 'Who' ),      Q(pub_date = date( 2005 ,  5 ,  2 )) | Q(pub_date = date( 2005 ,  5 ,  6 )) )

... roughly translates into the SQL:

SELECT * from polls WHERE question LIKE 'Who%'
    AND (pub_date = '2005-05-02' OR pub_date = '2005-05-06')

Lookup functions can mix the use of Q objects and keyword arguments. All arguments provided to a lookup function (be they keyword arguments or Q objects) are 「AND」ed together. However, if a Q object is provided, it must precede the definition of any keyword arguments. For example:

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Poll.objects.get(      Q(pub_date = date( 2005 ,  5 ,  2 )) | Q(pub_date = date( 2005 ,  5 ,  6 )),      question__startswith = 'Who' )

... would be a valid query, equivalent to the previous example; but:

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# INVALID QUERY Poll.objects.get(      question__startswith = 'Who' ,      Q(pub_date = date( 2005 ,  5 ,  2 )) | Q(pub_date = date( 2005 ,  5 ,  6 )))

... would not be valid.

　　

更新　

Updating multiple objects at once

1 2	# Update all the headlines with pub_date in 2007. Entry.objects. filter (pub_date__year = 2007 ).update(headline = 'Everything is the same' )

在原有數據的基礎上批量自增

Calls to update can also use F expressions to update one field based on the value of another field in the model. This is especially useful for incrementing counters based upon their current value. For example, to increment the pingback count for every entry in the blog:

1	>>> Entry.objects. all ().update(n_pingbacks = F( 'n_pingbacks' )  +  1 )

However, unlike F() objects in filter and exclude clauses, you can’t introduce joins when you use F() objects in an update – you can only reference fields local to the model being updated. If you attempt to introduce a join with an F() object, a FieldErrorwill be raised:

1 2	# THIS WILL RAISE A FieldError >>> Entry.objects.update(headline = F( 'blog__name' ))

 

 

Aggregation（聚合）

  示例models

  經常使用聚合場景需求

更多聚合查詢例子:https://docs.djangoproject.com/en/1.9/topics/db/aggregation/ 

　　

　　

　　

用戶認證　

 

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from  django.contrib.auth  import  authenticate user  =  authenticate(username = 'john' , password = 'secret' ) if  user  is  not  None :      # the password verified for the user      if  user.is_active:          print ( "User is valid, active and authenticated" )      else :          print ( "The password is valid, but the account has been disabled!" ) else :      # the authentication system was unable to verify the username and password      print ( "The username and password were incorrect." )

How to log a user out¶

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from  django.contrib.auth  import  logout   def  logout_view(request):      logout(request)      # Redirect to a success page.

-----from old boy