Model View Controller Pattern


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Model View Controller is the most commonly used design pattern. Developers find it easy to implement this design pattern.

Following is a basic architecture of the Model View Controller −

Architecture

Let us now see how the structure works.

Model

It consists of pure application logic, which interacts with the database. It includes all the information to represent data to the end user.

View

View represents the HTML files, which interact with the end user. It represents the model’s data to user.

Controller

It acts as an intermediary between view and model. It listens to the events triggered by view and queries model for the same.

Python code

Let us consider a basic object called “Person” and create an MVC design pattern.

Model.py

import json

class Person(object):
   def __init__(self, first_name = None, last_name = None):
      self.first_name = first_name
      self.last_name = last_name
   #returns Person name, ex: John Doe
   def name(self):
      return ("%s %s" % (self.first_name,self.last_name))
		
   @classmethod
   #returns all people inside db.txt as list of Person objects
   def getAll(self):
      database = open('db.txt', 'r')
      result = []
      json_list = json.loads(database.read())
      for item in json_list:
         item = json.loads(item)
         person = Person(item['first_name'], item['last_name'])
         result.append(person)
      return result

It calls for a method, which fetches all the records of the Person table in database. The records are presented in JSON format.

View

It displays all the records fetched within the model. View never interacts with model; controller does this work (communicating with model and view).

from model import Person
def showAllView(list):
   print 'In our db we have %i users. Here they are:' % len(list)
   for item in list:
      print item.name()
def startView():
   print 'MVC - the simplest example'
   print 'Do you want to see everyone in my db?[y/n]'
def endView():
   print 'Goodbye!'

Controller

Controller interacts with model through the getAll() method which fetches all the records displayed to the end user.

from model import Person
import view

def showAll():
   #gets list of all Person objects
   people_in_db = Person.getAll()
   #calls view
   return view.showAllView(people_in_db)

def start():
   view.startView()
   input = raw_input()
   if input == 'y':
      return showAll()
   else:
      return view.endView()

if __name__ == "__main__":
   #running controller function
   start()


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