I'm trying to jump from the world of FBV to CBV, but running into an immediate problem...which i'm sure must be pretty common and solvable and I just don't know how...

I'm inheriting the general View class into my parent class, which has all the code from my FBV.

I created a sub-class which inherits from the parent, and the page still loads fine. Good initial start!

But now, I want to utilize the inheritance feature of CBV. I want to move (or override) multiple unique pieces in the parent to the child. I just want to leave the "common" code in the parent, and then all unique things to the child (and eventually other child classes).

For example...I have about 1,000 lines of code in parent. And I will need to move / override probably 1/3 of it into child classes. But that 1/3 is scattered from the beginning to the end of the parent. It's not like the parent will be the complete first 1/2 of the code, and then the child classes will be last 1/2.

Which presents 2 problems...

A) For example, when I want to override a particular section of code in the child, some of the variables necessary to come up with the result of that chunk of code, are in the beginning part of the parent class, which I don't need in the child...It seems like the only way to accomplish this is almost having to copy the entire code in the parent to the child class, which feels like its defeating the purpose of OOP / inheritance / DRY.

B) Because there's bits and pieces I want to override, scattered throughout the parent, I don't know how the code will be able to really know the order to execute...for example...If i'm moving lines 50-100, 340-600, 880-900, to the subclass (because these lines will be different per child class)...I still need the code to really execute them in the original order, in order to be work properly. It almost feels like I need to somehow tell it "do this method in the parent first, then go to the child and do this one, then back to the parent and continue, etc"

Sorry for no code snippets. I think this is more theoretical understanding at this point.

Any help is greatly appreciated!!!

CodePudding user response：

When you are dealing with classes and inheritance you are dealing with items that hold state (attributes) and functions that manipulate that state and query it (methods). A class is a 'template' of what an instance of that class should have as far as attributes and function.

You instantiate the class (in python by calling the Class name as a function) and passing in any data the class will need. This is presented to the init method as arguments. you also get a reference to the instance in the self variable (first argument of instance methods). You can use the self variable to save the values passed in with the instance. Your Class name invocation will return a reference to the instance of the class. Programs use returned value to call the methods on your instance (example: myinstance.mymethod() ). This will decide the order of execution of the functions for the instance of your class. Each function called will be passed the self variable which allows you to refer again to the values you saved as attributes for the instance (like in the init method).

In your Django framework you seem to be using, the CBV framework defines when certain methods will be called (get, post, etc). once they are active if you need to call another method in the class you can do a

self.first_method_to_run()
self.second_method_to_run()

within the get/post/whatever method. this will run them in that order and will look for the method (first in the child class and run it starting there and then in the parent class and run it from there) in the class hierarchy.

Hope this helps clear some things up.

CodePudding user response：

As mentioned by @lhasaDad above, just need to call the methods in order. Note they can be written outside the Post() method, but need to be called in the Post() method!