Framework introduction

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MVC Pattern

MVC（Model-view-controller） Is a design pattern widely used in software engineering . Especially suitable for GUI Design and WEB Application design , It is convenient to modify the presentation layer of the application without affecting the business logic . Or modify the underlying business logic without 
 Affect other parts . Now new WEB Many development frameworks adopt MVC Pattern 

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MVC Model is introduced

Django Medium MVC The model is divided into three parts

Model（ Model ）： Database related , Objects responsible for business objects and databases （ORM）

　　　　　　　　　 At the model level , It includes business logic process and state , These models contain methods for applying processing data . The design of the business model is MVC Design core of pattern 

　　　　　Template（ Templates ）： Put all of them html file 

View（ View ）： Responsible for business logic , And call when appropriate Model and Template

　　　　　　　　 The view hierarchy contains the end-user interface , Including input data and output display . For specific applications , There may be multiple views showing 

Controller( Control layer )： It can realize the specific control of the application . Control hierarchy can combine model hierarchy and view hierarchy , Jointly complete specific application requests .

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　　 Besides ,Django One more URL The dispenser . Its function is to make one by one URL Page requests of are sent to different Views Handle ,Views Call the corresponding Model and Template.

MVC Advantages and disadvantages of

advantage

1. Each performs his duty , They don't interfere with each other 

 stay MVC In the pattern , Each of the three levels performs its duties , So once the requirements of which layer change , You just need to change the code in the corresponding layer without affecting the code in other layers .

2. It is conducive to the division of labor in development 

 stay MVC In the pattern , Because the system is separated by layers , Then we can better realize the division of labor in development . Web designers can develop the view layer of JSP, Developers familiar with the business can develop the business layer , Other developers can develop the control layer .

3. Facilitate reuse of components 

 Layering is more conducive to the reuse of components . For example, the control layer can be separated into a functional component , The view layer can also be made into a general operation interface .

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shortcoming

MVC The shortcomings are reflected in the following aspects ：

(1) It increases the complexity of system structure and implementation . For a simple interface , Follow strictly MVC, Make model 、 View separate from controller , It increases the complexity of the structure , And may produce too many update operations , Reduce operating efficiency .

(2) Too close connection between view and controller . View and controller are separated from each other , But it's really tightly connected components , The view has no controller , Its application is very limited , vice versa , This hinders their independent reuse .

(3) View inefficient access to model data . Depending on the model operation interface , Views may need to be called multiple times to get enough display data . Unnecessary frequent access to unchanging data , It will also damage operational performance .

(4)  at present , Most advanced interface tools or constructors don't support MVC Pattern . Adapt these tools to MVC The cost of needing and building separate parts is high , This leads to the use of MVC The difficulty of .MVC

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MTV Pattern

Django The design pattern of the framework is based on MVC The idea of frame , It's also divided into three parts , To reduce the coupling between the parts .

Django The difference of the framework is that it is divided into three parts ：Model（ Model ）、Template（ Templates ） and View（ View ）, That is to say MTV frame .

Django Of MTV Pattern

Model( Model )： Objects responsible for business objects and databases (ORM)

Template( Template )： Responsible for how to display the page to users

View( View )： Responsible for business logic , And call when appropriate Model and Template

Besides ,Django One more urls The dispenser , Its function is to make one by one URL Page requests are distributed to different view Handle ,view Call the corresponding Model and Template

Django Frame diagram

APP

One Django The project can be divided into many APP, Code used to isolate different functional modules .

Command line creation

python manage.py startapp app01

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Use PyCharm establish

In the command window that pops up below, enter ：

startapp app01

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route

View

Templates

Model

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