Accelerating Information Technology Innovation

Transcription

1 Accelerating Information Technology Innovation Nigeria Summer 2011 Django

2 The Big Picture Google App Engine Mobile Web Browser/ Mobile Web App Your Django app

3 Mobile App Development Course Roadmap Django Back-End Google App Engine Google Datastore Mobile Applications SMS/USSD Mobile Web HTML CSS Front End Javascript/ JQuery Android Java Python with SL4A

4 Core Interface Client SMS Gateway GAE: Main Django App GAE: JSON API Local App GAE: Website Mobile Web Desktop Web

5 Development Tools Operating system Linux (Ubuntu) Integrated Development Environment Eclipse (Pydev) Version Control git (GitHub) mercurial (Bitbucket or Google project hosting) subversion (Google project hosting)

6 Web design Never design websites from scratch Two main options: Content Management Systems (CMS) A website straight out of the box Can be modified and customised Web frameworks Consists of code libraries that provides functionality for common components in a website, web app, or web service. Build your own CMS

7 Why CMS and Web Frameworks Eases coding for Working with forms Handling HTTP requests Templates for common HTML layouts URL mapping Database communication Session management Site security Allows you to focus on design and functionality rather than small details. In this class, we re going to use a Web Framework called Django

8 Frameworks: Model-View-Controller (MVC) A paradigm for organizing code often seen in web app frameworks Main idea is: Separate the storage and manipulation of data (the model) and the presentation of data (view) Use the Controller to communicate between the model and view Advantages Easier to develop and test model and view independently Easier for others to understand Exact roles of model, view, and controller depend on who you ask!

9 Model-View-Controller (MVC) (news site example) Controller Send request for a story Asks the model for the story and its user comments View Layout of stories on mobile phone or desktop browser Serves requested story Model News stories and images in a database User comments

10 Python Web Application Frameworks for Backend

11 Web application framework, written in Python Released 2005 Began with World Online, that needed to rapidly develop applications for news sites. Named after gypsy jazz guitarist Django Reinhardt ( ) Follows the Model-View- Controller paradigm Django

12 Why Django? Fast and easy development of web applications Modular and re-useable. Don t Repeat Yourself (DRY) principle Hides database details Active development and wide community support Successful Django sites Supported by Google App Engine

13 Model-View-Controller (MVC) (news site example) Controller Send request for a story Asks the model for the story and its user comments View Layout of stories on mobile phone or desktop browser Serves requested story Model News stories and images in a database User comments

14 Django Model-Template-View (MTV) (news site example) View Send request for a story Asks the model for the story and its user comments Template Layout of stories on mobile phone or desktop browser Serves requested story Model News stories and images in a database User comments

15 Django Architecture MVC (Traditional) Model View Controller MTV (Django) Model Template View

16 Google App Engine Google s cloud computing platform to develop and host web applications Distributed data storage service (The Datastore) Free up to 500 MB of storage and 5 million page views Saves the hassle and initial costs of setting up your own server equipment and software Supports Java and Python

17 Django: Projects and Apps Django works with projects and apps Apps are pluggable (any app can be in multiple projects) Feedback (App) Responder (App) Parser (App) Website (Project)

18 Getting Started with django 1. Setup website 2. Create the app(s) Set up the models Set up the views Create templates if needed Modify the urls 3. Update database 4. Start the server

19 1. Setup website django-admin.py startproject musicsite Creates musicsite in current directory Default file directory init.py manage.py settings.py urls.py An empty file that tells Python this directory is a Python package Command-line utility that lets you interact with this Django project in various ways Settings/configuration for this Django project The URL declarations for this Django project

20 2. Create the app cd musicsite django-admin.py startapp musicmanager Create app named musicmanager File directory init.py An empty file that tells Python this directory is a Python package models.py Contains classes that specify our models tests.py views.py Contains logic and functions for views

21 Django Model-Template-View (MTV) (news site example) View Send request for a story Asks the model for the story and its user comments Template Layout of stories on mobile phone or desktop browser Serves requested story Model News stories and images in a database User comments

22 Models What they are? Models are schema for your data Classes describing data in your app Classes with attributes for each data field Why do we use them? Avoid direct work with the database No need to handle database connections, timeouts, etc. Let django do it for you.

23 Django fields Define the field and django handles the rest: In models.py active = models.booleanfield() Django handles the rest: Bit value in sql database Represented as a checkbox on a webpage Validation of values Django has already implemented fields Can also implement custom fields

24 Name BooleanField CharField(max_length=x) DateField DateTimeField DecimalField(max_digits, decimal_places) Field FileField FloatField ImageField *** Don t use, unsupported IntegerField PositiveIntegerField TextField TimeField URLField Displays as Checkbox Single-line textbox Javascript calendar Javascript calendar, time picker Decimal numbers CharField that validates address File upload, stores path in database Floating point numbers Stores images Integer textbox Integer textbox for positive integers Multi-line textbox Time picker Textbox for URLs

25 Django Relationship Fields ForeignKey(foreign class) Many-to-one ManyToManyField(foreign class) Uses a temporary table to join tables together OneToOneField(foreign class) Enforces uniqueness

26 Field Options blank: if True, field is allowed to be blank. default is False. null: if True, empty fields will be stored as NULL in database. choices: list of 2-tuples, will create a select box instead of CharField class Foo(models.Model): GENDER_CHOICES = ( ('M', 'Male'), ('F', 'Female'), ) gender = models.charfield(max_length=1, choices=gender_choices) default: default value for a field primary_key: if True, this field is the primary key for the model unique: if True, this will have to be unique throughout the table verbose_field_name: provides a human readable file name

27 DateField and DateTimeField options Auto_now Any time the object is saved, the field will be updated with the current time. Auto_now_add The time will always be equal to the creation date of the object.

28 Model Methods unicode (): Equivalent of tostring used for autogenerated admin pages get_absolute_url() Used for deciding URLs that reference a specific object

29 2. Create the app: Edit models.py class Musician(models.Model): first_name = models.charfield(max_length=50) sur_name = models.charfield(max_length=50) instrument = models.charfield(max_length=100) def unicode (): return sur_name+, +first_name class Album(models.Model): artist = models.foreignkey(musician) name = models.charfield(max_length=100) release_date = models.datefield() num_stars = models.integerfield() def unicode (): return name

30 Creating Models Manually >>> from music.models import Musician Not in database yet >>> m1 = Musician(first_name='Femi', sur_name='kuti', instrument='saxophone') >>> m1.save() Now in database >>> m2 = Musician(first_name='Eric', sur_name='clapton', instrument='guitar') >>> m2.save()

31 Getting data from database: Managers and QuerySets Manager class interface between the database and the app Musician.objects returns a Manager object Methods include filter(), exclude(), and order_by() QuerySet class collection of objects from the database Musician.objects.get_query_set.all() or the shorter Musician.objects.all() returns QuerySet objects We can refine a QuerySet to produce another QuerySet Methods include filter(), exclude(), and order_by()

32 Filter Data exact: gets an exact match Musician.objects.filter (instrument exact= saxophone! Musician.objects.filter(instrument='saxophone') # exact is implied contains: find if a match is contained inside a field Musician.objects.filter (instrument contains= sax ) icontains: case insensitive contains Musician.objects.filter (last_name icontains= kuti')

33 Ordering Musician.objects.order_by('- last_name', first_name ) First orders by last_name in descending order (hence the negative sign). If there are last_names that are equivalent, then first_name is ordered in ascending order.

34 Values Musician.objects.values() Returns a ValueQuerySet, which returns a list of dictionaries when executed Musician.objects.values ( last_name', first_name') Returns only the fields last_name and first_name in the dictionary

35 Distinct Musician.objects.distinct() If there are any duplicate rows, only one is returned This will rarely work like this, because you often will already have a distinct field, like an id Musician.objects.values( last_name, first_name ).distinct() This will get all unique last_namefirst_name combinations Notice the chaining here!

36 Slicing Musician.objects.all()[:5] Gets the first 5 Musician objects

37 Get Gets a single row raises MultipleObjectsReturned if more than one object was found. The MultipleObjectsReturned exception is an attribute of the model class. raises a DoesNotExist exception if an object wasn't found for the given parameters. This exception is also an attribute of the model class. Musician.objects.get(id=5) Returns a single QuerySet if there is a row that exists, otherwise an error ensues Musician.objects.filter(id=5)[0] Similar, except no exceptions are thrown

38 When are QuerySets evaluated? Iteration for person in Musician.objects.all(): print person.first_name, person.last_name Boolean if Musician.objects.filter(instrument= voice"): print "There is at least one Musician that sings"

39 Creating Models Manually >>> from music.models import Musician >>> m1 = Musician(first_name='Jimi', last_name='hendrix', instrument='guitar ) >>> m1.save() >>> m2 = Musician(first_name="Eric", last_name= Clapton, instrument='guitar ) >>> m2.save() >>> Musician_list = Musician.objects.all() >>> Musician_list [<Musician: Hendrix, Jimi>, <Musician: Clapton, Eric>] #remember the unicode!!

40 Filtering ( Musician.objects.filter(first_name= Jimi <<< [<Musician: Hendrix, Jimi>] ( Musician.objects.filter(instrument= guitar <<< [<Musician: Hendrix, Jimi>, <Musician: Clapton, Eric>] #returns a QuerySet, not an individual Model Object >>>Musician.objects.filter ( last_name contains= Clap ) [<Musician: Clapton, Eric>] #double underscore!!

41 Getting >>>Musician.objects.get(first_name= Jimi ) <Musician: Hendrix, Jimi> #returns single object >>>Musician.objects.get(instrument= violin ) Error! DoesNotExist >>>Musician.objects.get(instrument= guitar ) Error! MultipleObjectsReturned #use try/except when using get.

42 Ordering ( Musician.objects.order_by(-last_name <<< [<Musician: Hendrix, Jimi>, <Musician: Clapton, Eric>] Easier way: add class Meta to Model class class Musician(models.Model): first_name = models.charfield(max_length=50) last_name = models.charfield(max_length=50) instrument = models.charfield(max_length=100) def unicode (): return last_name+, +first_name class Meta: ordering = [-last_name]

43 More Functionality >>>m1.instrument= drums >>>m1.save() #updates ALL rows, could lead to race condition >>>Musicians.objects.filter(id=12).update ( instrument= bass ) #updates only instrument row Chaining >>>Musicians.objects.filter (" instrument="guitar").order_by("-last_name ) [<Musician: Hendrix, Jimi>, <Musician: Clapton, Eric>]

44 Rules of Django Models 1. If you update a model, UPDATE DATABASE python manage.py syncdb 2. All classes extend models.model 3. Only apps have Models 4. Django doesn't save objects until you call save() method

45 Tips for Django Models 1. Keep code clean 2. Name your variables well 3. Don t think too much about the database 4. Always create a unicode () method

46 Django Model-Template-View (MTV) (news site example) View Send request for a story Asks the model for the story and its user comments Template Layout of stories on mobile phone or desktop browser Serves requested story Model News stories and images in a database User comments

47 Views Views are the logical interface between data (Models) and presentation (Templates) Defined in views.py inside the appfolder EVERY view takes a request object as first parameter EVERY view returns an HttpResponse object from django.http import HttpResponse def hello(request): return HttpResponse("Hello world")

48 Our views.py from django.template import Context, loader from django.http import HttpResponse from models import Musician def musicians_list(request): musician_list = Musician.objects.all() t = loader.get_template('musicians/list.html') c = Context({'musician_list': musician_list,}) return HttpResponse(t.render(c)) def musicians_detail(request,id): musician = Musician.objects.get(pk=id) t = loader.get_template('musicians/detail.html') c = Context({'musician': musician,}) return HttpResponse(t.render(c))

49 Use urls.py to direct HTTP requests to views # urls.py in musicsite from django.conf.urls.defaults import * from django.contrib import admin urlpatterns = patterns('', url(r'^admin/', include(admin.site.urls)), url(r'^musicians/, include(musicsite.musicians.urls )) ) # urls.py in musicians from django.conf.urls.default import * import views urlpatterns = patterns('', url(r'^list/$',views.musicians_list,name='musicians_list'), url(r'^detail/(?p<id>\d+)/ $',views.musicians_detail,name='musicians_detail'), )

50 Request Life Cycle 1. User requests to view URL 2. Django determines the root URLconf by looking at the ROOT_URLCONF setting. 3. Django looks at all of the URLpatterns in the URLconf for the first one that matches the URL 4. If it finds a match, it calls the associated view function. Repeats Steps 3-4 if redirected to another urls.py 5. The view function returns an HttpResponse. 6. Django converts the HttpResponse to the proper HTTP response, which results in a Web page.

51 Request Life Cycle User requests musicians/detail/ 2 Django determines root URLConf is urls.py in musicsite Django looks up musicians/detail/ 2 in urls.py of musicsite Django display the HTTPResponse as a web page There s a match, and Django calls the associated view function There s a match, but Django must look up detail/2 in musicians urls.py

52 Dynamic Content # urls.py from django.conf.urls.defaults import * from mysite.views import hello, current_datetime, hours_ahead urlpatterns = patterns('', (r'^hello/$', hello), (r'^time/$', current_datetime), )

53 Dynamic Content # views.py from django.http import HttpResponse import datetime def hello(request): return HttpResponse("Hello world") def current_datetime(request): now = datetime.datetime.now() html = "<html><body>it is now %s.</body></ html>" % now return HttpResponse(html)

54 Django Model-Template-View (MTV) (news site example) View Send request for a story Asks the model for the story and its user comments Template Layout of stories on mobile phone or desktop browser Serves requested story Model News stories and images in a database User comments

55 Templates A text-based template for HTML, CSS, XML, JavaScript, etc. Mixture between hard-coded text and abstractions Abstractions Variables Tags Re-useable and extensible

56 weather.html <html> <head> <title> Weather </title> </head> <body> <p>today s weather in {{ city }} is {{ description }}.</p> <div id= temperature > {% for day in thisweek %} <li> On {{ day.date }}, the temperature will be {{ day.temperature }}. </li> {% endfor %} </div> <div id="ads"> {% block ads %} Click on these ads! {% endblock %} </div> </body> </html>

57 Hard-coded Text in weather.html <html> <head> <title> Weather </title> </head> <body> <p>today s weather in {{ city }} is {{ description }}.</p> <div id= temperature > {% for day in thisweek %} <li> On {{ day.date }}, the temperature will be {{ day.temperature }}. </li> {% endfor %} </div> <div id="ads"> {% block ads %} Click on these ads! {% endblock %} </div> </body> </html>

58 Variables {{ variable }} If variable doesn t exist, then output TEMPLATE_STRING_IF_INVALID (default: empty string ) {{ variable.attribute }} 1. Dictionary Lookup. variable[ attribute ] 2. Attribute Lookup. variable.attribute 3. Method Call. variable.attribute() 4. List-index Call. variable[attribute]

59 Filters Modify the output of variables {{ variable filter }} foo := Hello World bar := [ a, b, c ] {{ foo lower }} --> hello world {{ bar length }} --> 3 {{ bar slice: :2 }} --> [ a, b ] {{ baz default: error! }} --> error!

60 Tags for loops if clauses comments blocks and many more built-in tags (look them up!) {% tag %} {% endtag %}

61 Tags in weather.html <html> <head> <title> Weather </title> </head> <body> <p>today s weather in {{ city }} is {{ description }}.</p> <div id= temperature {% for day in thisweek %} <li> On {{ day.date }}, the temperature will be {{ day.temperature }}. </li> {% endfor %} </div> <div id="ads"> {% block ads %} Click on these ads! {% endblock %} </div> </body> </html>

62 For loops {% for x in y %} logic {% endfor %} fruit_basket := { apples, oranges, pineapples } {% for fruit in fruit_basket %} <li>{{ fruit }}</li> {% endfor} <li>apples</li> --> <li>orange</li> <li>pineapples</li>

63 If clauses {% if <condition> %} logic {% else %} logic {% endif %} {% if rain > 1 } Buy an umbrella for {{ price1 }} {% else %} Buy sunglasses for {{ price2 }} {% endif %}

64 Comments {% comment %} This comment won t be displayed! {% endcomment} Ignore everything inside tag For inline comments, use {# blah blah blah #}

65 Template Inheritance Define extensible parts of a template with block tags {% block name %} {% endblock %} Create child templates that can extend blocks Load parent template with {% extends parent_template %}

66 Template Inheritance In child template, redefine contents of the parent s block tag similar to overriding methods in class inheritance If a block tag is not redefined, then use contents of block tag in parent {{ block.super }} explicitly refers to contents of block tag in parent

67 weather.html <html> <head> <title> Weather </title> </head> <body> <p>today s weather in {{ city }} is {{ description }}.</p> <div id= temperature > {% for day in thisweek %} <li> On {{ day.date }}, the temperature will be {{ day.temperature }}. </li> {% endfor %} </div> <div id="ads"> {% block ads %} Click on these ads! {% endblock %} </div> </body> </html>

68 ads.html {% extends "weather.html" %} {% block ads %} {% if rain > 1 } Buy an umbrella! {% else %} Buy sunglasses! {% endif %} {% endblock %}

69 Context city = Nairobi descrip1on = 'sunny thisweek = [dict(date='thursday',temperature=20), dict(date='friday', temperature=25), dict(date='saturday', temperature=22)] rain = 3 Displayed by browser Today s weather in Nairobi is sunny. On Thursday, the temperature will be 20. On Friday, the temperature will be 25. On Saturday, the temperature will be 22. Click on these ads! Buy an umbrella!

70 Templates Mixture of hard-coded text and abstractions Abstractions often look like and function like Python code, but you can t run arbitrary Python code Lookup list of built-in filters and tags in Django Customize your own filters and tags Complex logic with arbitrary Python should be performed by views.py and only the processed variables should be passed to a template

71 Django Model-Template-View (MTV) (news site example) View Send request for a story Asks the model for the story and its user comments Template Layout of stories on mobile phone or desktop browser Serves requested story Model News stories and images in a database User comments

72 Forms You don t want to give users access to the admin interface, but you still want them to be able to add/update data 72

73 Basic HTML form <html>! <head>! <title>contact us</title>! </head>! <body>! <h1>contact us</h1>! <form action="/contact/" method="post">! <p>subject: <input type="text" name="subject"></p>! <p>your (optional): <input type="text" name=" "></p>! <p>message: <textarea name="message" rows="10" cols="50"></textarea></p>! <input type="submit" value="submit">! </form>! </body>! </html>! 73

74 Django Form from django import forms! class ContactForm(forms.Form):! subject = forms.charfield()! = forms. field(required=false)! message = forms.charfield()! 74

75 Form Methods print ContactForm()! Prints out HTML code for the form with a table layout print ContactForm().as_ul()! Prints out HTML code for the form as an unordered list print ContactForm().as_p()! Prints out HTML code for the form as paragraphs 75

76 Form Validation f = ContactForm({'subject': 'Hello', ' ': 'adrian@example.com', 'message': 'Nice site!'})! When you create an instance of a form using a dictionary as an argument, it will use those values to fill in the form on the server 76

77 Form validation f.is_bound! Returns true if the form has been bound to data f.is_valid()! Returns true if all values passed to the form are valid F.cleaned_data! Returns a dictionary with all data cleaned up 77

78 Form Error Handling Error handling is done automatically by the form and errors are saved into an instance variable called errors 78

79 Creating a view def contact(request):! if request.method == 'POST':! form = ContactForm(request.POST)! if form.is_valid():! cd = form.cleaned_data! send_mail(! cd['subject'],! cd['message'],! cd.get(' ', 'noreply@example.com'),! ['siteowner@example.com'],! )! return HttpResponseRedirect('/contact/thanks/')! else:! form = ContactForm()! return render_to_response('contact_form.html', {'form': form})! 79

80 New contact_form.html <html>! <head>! <title>contact us</title>! </head>! <body>! <h1>contact us</h1>! {% if form.errors %}! <p style="color: red;">! Please correct the error{{ form.errors pluralize }} below.! </p>! {% endif %}! <form action="" method="post">! <table>! {{ form.as_table }}! </table>! <input type="submit" value="submit">! </form>! </body>! </html>! 80

81 Making it better Make message be a Textarea instead of a textbox: message = forms.charfield (widget=forms.textarea)! Limit subject length: subject = forms.charfield (max_length=100)! Adding labels = forms. field (required=false, label='your address')! 81

82 Making it better Adding initial Values def contact(request):! if request.method == 'POST':!...! else:! form = ContactForm(! initial={'subject': 'I love your site!'}! )! return render_to_response('contact_form.html', {'form': form})! 82

83 Making it better Custom validation: Inside your form class, you can create custom methods that will clean your variable and throw an exception if it fails The Forms class will automatically look for the pattern clean_fieldname, so we can use clean_subject, clean_ , or clean_message! 83

84 Making it better def clean_message(self):! message = self.cleaned_data ['message']! num_words = len (message.split())! if num_words < 4:! raise forms.validationerror("not enough words!")! return message! 84

85 Do I have to do that every time? No. Only if you re using a form that s not controlled by a model. 85

86 Forms from Models Using our example of a Musician model: from django.forms import ModelForm! class MusicianForm(ModelForm):! class Meta:! model = Musician! That s it. 86

87 Forms from Models To create an add form from your class: form = MusicianForm() To create a change form: mus = Musician.objects.get (first_name= Jimi ) Form = MusicianForm(instance=mus) 87

88 Forms from Models Saving the input from a form f = MusicianForm(request.POST)! new_musican = f.save()! Restricting fields for the form: class PartialMusicianForm(ModelForm):! class Meta:! model = Musician! fields = ( sur_name', first_name')!!!! exclude = ( instrument )! 88