ORM Lab (CodeGrade)

Close

• Due No Due Date
• Points 1
• Submitting an external tool

Learning Goals

• Map a Python class to a database table.
• Persist a one-to-many relationship.
• Define property methods to manage attributes.

Instructions

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.

This lab involves enhancing the company data model from the ORM lessons. You will implement a class named Review that encapsulates an annual performance review for an employee. There is a one-to-many relationship between Employee and Review.

• An employee may have many reviews.
• A review is for one employee.
• A review includes an attribute for the year as well as a summary of the employee's performance.

The Department and Employee classes contain the completed solutions from the ORM lessons. You will add functionality for the new Review class in this lab.

Environment

The environment is initialized in lib/__init__.py to generate a sqlite3.Connection object CONN, and a sqlite3.Cursor object CURSOR.

Implementing Review

The Review class contains the following methods already implemented for you:

• __init__ initializes attributes for the review year, summary, and associated employee. It also initializes the id attribute to a default value of None.
• __repr__ returns a formatted string containing the attribute values.
• create_table creates a "reviews" database table.
• drop_table drops the "reviews" database table.

Edit the Review class to add the following ORM methods (you will add property methods in a subsequent step):

save()

The instance method save() should persist the Review object to the "reviews" table:

• Insert a new row with the year, summary, and employee_id values of the current Review instance.
• Update the object id attribute using the primary key value of new row.
• Save the object in local dictionary using table row's PK as dictionary key.

create()

This is a class method that should:

• Create a new Review instance using the parameter values.
• Save the new Review instance to the "reviews" table.
• Return the new Review instance.

Think about how you can re-use the save() method to help with this one.

instance_from_db()

This class method should return a Review instance having the attribute values from the table row. You should check the dictionary for an existing instance using the row's primary key, and set the instance attributes to the row data if found. If the dictionary does not contain a previously persisted object with that id, create a new Review instance from the row data and add it to the dictionary. The method should return the cached object.

find_by_id()

This class method takes in an id as a parameter, and should return a single Review instance corresponding to the row in the "reviews" table with that same id, or None is no such row exists in the table.

update()

This instance method should update the year, summary and employee_id columns for a "reviews" table row based on the id of the current object.

delete()

This instance method should delete a "reviews" table row based on the id of the current object. It will also remove the instance from the all dictionary and set the current object's id attribute to None.

get_all()

This class method should return a list of Review instances for every row in the "reviews" table.

You can test your methods by running the tests in the "lib/testing/review_orm_test.py" file:

pytest lib/testing/review_orm_test.py

You can also experiment by running python lib/debug.py and calling the new ORM methods at the ipbd> prompt:

ipdb> Review.get_all()

Review Properties

Let's add property methods to set rules for the Review attributes as follows:

• year should be an integer that is greater than or equal to 2000.
• summary should be a non-empty string.
• employee_id should be the id of an Employee class instance that has been persisted into the "employees" table.

You can test your methods by running the tests in the "lib/testing/review_property_test.py" file:

pytest lib/testing/review_property_test.py

Update Employee to get a list of associated Review instances

Update the Employee class with a new method reviews() for getting associated Review instances that have been persisted to the database.

reviews()

This instance method should query the "reviews" table to get all rows where the foreign key column employee_id matches the id of the current Employee instance. The method should return a list of Review instances for each matching table row.

NOTE: To avoid issues with circular imports, embed import the Review class within the reviews() method rather than at the module level.

You can test your methods by running the tests in the "lib/testing/employee_orm_test.py" file:

pytest lib/testing/employee_orm_test.py

Submit your completed lab

Check to make sure all tests pass:

pytest -x

Once all of your tests pass, commit and push your work using git to submit your solution.