Many-to-many Object Relationships Lab

Learning Goals

• Create a Many-to-many relationship using an intermediary class.
• Write aggregate methods.

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Key Vocab

• Class: a bundle of data and functionality. Can be copied and modified to accomplish a wide variety of programming tasks.
• Object: the more common name for an instance. The two can usually be used interchangeably.
• Object-Oriented Programming: programming that is oriented around data (made mobile and changeable in objects) rather than functionality. Python is an object-oriented programming language.
• Function: a series of steps that create, transform, and move data.
• Method: a function that is defined inside of a class.

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Introduction

In this lab we will implement a one-to-many relationship between a Author, Book, and Contract.

This is a test-driven lab. Run pipenv install to create your virtual environment and pipenv shell to enter the virtual environment. Then run pytest -x to run your tests. Use these instructions and pytest's error messages to complete your work in the lib/ folder.

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Instructions

Create a Book class that has the following attributes: title (string)

Create an Author class that has the following attributes: name (string)

Create a Contract class that has the following properties: author (Author object), book (Book object), date (string), and royalties (int).

All classes should also keep track of all members using a class variable.

• The author property should be an instance of the Author class, while the book property should be an instance of the Book class. The date property should be a string that represents the date when the contract was signed, while the royalties property should be a number that represents the percentage of royalties that the author will receive for the book.
  • All setters should raise Exception upon failure.

The Author class should have the following methods:

• contracts(self): This method should return a list of related contracts.
• books(self): This method should return a list of related books using the Contract class as an intermediary.
• sign_contract(book, date, royalties): This method should create and return a new Contract object between the author and the specified book with the specified date and royalties
• total_royalties(): This method should return the total amount of royalties that the author has earned from all of their contracts.

The Contract class should have the following methods:

• A class method contracts_by_date(cls, date): This method should return all contracts that have the same date as the date passed into the method.

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Resources

• Python classes