learn-co-curriculum / phase-3-object-relations-practice-code-challenge-students-one-many

Object Relations Practice Code Challenge - Students

Introduction

For this assignment, we'll be working with a Students domain.

We have two models: Cohort and Student.

For our purposes, a Cohort has many Studentss and a Student belongs to a Cohort.

Student - Cohort is a one to many relationship.

Note: You should draw your domain on paper or on a whiteboard before you start coding. Remember to identify a single source of truth for your data.

Topics

• Active Record Migrations
• Object Relationships
• Active Record Queryng

Instructions

To get started, run bundle install while inside of this directory.

Build out all of the methods listed in the deliverables. The methods are listed in a suggested order, but you can feel free to tackle the ones you think are easiest. Be careful: some of the later methods rely on earlier ones.

Remember! This code challenge does not have tests. You cannot run rspec and you cannot run learn. You'll need to create your own sample instances so that you can try out your code on your own. Make sure your associations and methods work in the console before submitting.

We've provided you with a tool that you can use to test your code. To use it, run rake console from the command line. This will start a pry session with your classes defined. You can test out the methods that you write here. You are also encouraged to use the seeds.rb file to create sample data to test your models and associations.

Writing error-free code is more important than completing all of the deliverables listed - prioritize writing methods that work over writing more methods that don't work. You should test your code in the console as you write.

Similarly, messy code that works is better than clean code that doesn't. First, prioritize getting things working. Then, if there is time at the end, refactor your code to adhere to best practices.

Before you submit! Save and run your code to verify that it works as you expect. If you have any methods that are not working yet, feel free to leave comments describing your progress.

What You Already Have

The starter code has migrations and models for the initial Cohort and Student models, and seed data for some Cohorts and Students. The tables currently look like this:

students Table

Column	Type
name	string
age	integer
email	string

cohorts Table

Column	Type
name	string
current_mod	integer

You will need to create a migration to establish the relationship between these two tables. You'll need to add one additional column to one of these existing tables to create the relationship.

Remember: a Cohort has many Students and a Student belongs to a Cohort.

Deliverables

Write the following methods in the classes in the files provided. Feel free to build out any helper methods if needed.

Deliverables use the notation # for instance methods, and . for class methods.

Remember: Active Record give your classes access to a lot of built-in methods! Keep in mind what methods Active Record gives you access to on each of your classes when you're approaching the deliverables below.

Migrations

Before working on the rest of the deliverables, you will need to set up the migration files to establish the relationship between a Student and a Cohort.

• A Student belongs to a Cohort. Update the existing migrations file(s) to reflect this relationship.

Once you've updated the migrations, run rake db:migrate to run the migrations and set up the database. Then use the seeds.rb file to create instances of Students and Cohorts to so you can test your relationships.

Once you've successfully created the migration, work on building out the following deliverables.

Object Relationship Methods

Use Active Record association macros and Active Record query methods where appropriate (i.e. has_many, has_many through, and belongs_to).

Student

• Student#cohort
  • should return the Cohort instance for this student

Cohort

• Cohort#students
  • returns a collection of all Student instances for this cohort

Aggregate and Association Methods

Student

• Student#current_mod
  • returns the current mod for this student's cohort

Cohort

• Cohort#add_student
  • takes a name (as a String) and an age (as an Integer) and adds a new student to this cohort
• Cohort#average_age
  • returns the average age of all the students in the cohort as a Float
• Cohort#total students
  • returns the total number of students in the cohort as an Integer
• Cohort.biggest
  • returns a Cohort instance for the cohort with the most students
• Cohort.sort_by_mod
  • returns all cohorts, sorted by current_mod from lowest to highest

Rubric

Active Record Associations

1. No associations, no foreign key on the table.
2. Associations attempted in the model but are incorrect; foreign key is on a table but in the wrong spot.
3. Relationships properly created. Associations lead to the correct behavior but may have used the wrong macro or manually written out the methods the macro builds for us.
4. Relationships properly created, save minor mistakes in advanced deliverables. May implement advanced query methods with iterators instead of using built-in methods.
5. Relationships properly created. Advanced query methods use appropriate built-in methods.

Build classes using OO Ruby Syntax

1. Class code has a syntax or runtime error. Code does not run at all, or exits with an error, or most Object-oriented deliverables are not implemented.
2. No syntax errors. Some deliverables function correctly. Mixes up syntax for class and instance methods, refers to variables in the wrong scope, or uses self incorrectly, leading to logical errors. Method and variable names do not correspond to their respective behavior or data types. Methods might be duplicated, or code includes unused methods without a clear purpose.
3. Correct class syntax for the deliverables submitted. May be incomplete or missing deliverables. Most code generally expresses intent: method and variable names match their behaviors and data types. Methods are not duplicated. Code does not have unused or methods without a clear purpose.
4. Correct class syntax for all of the submitted code. Code express intent: method and variable names indicate their behavior and data types. Some deliverables might not be complete. No methods are duplicated.
5. Correct class syntax for all deliverables, all deliverables complete. Code expresses intent: method and variable names indicate their behavior and data types, with the correct pluralization. No methods are duplicated. All methods have a clear purpose. Shared functionality is factored out into helper methods. Appropriate use of attr_* macros.

Model relationships using Ruby

1. Submitted code does not relate models to each other through methods or data.
2. Models relate to each other, but incompletely. Relationship methods are missing or have logic errors, store data on the wrong model, or are missing a single source of truth.
3. Models relate to each other as specified in the instructions. Data is stored on the correct models, relationship methods are defined on the right models, and the logic correctly implements the relationships. Aggregate methods using the relationships may be incomplete or have errors.
4. Models relate to each other as specified in the instructions. Aggregate methods work, but might not use helper methods effectively.
5. Models relate to each other as specified in the instructions. Aggregate methods use helper methods effectively.

Solve problems with collections of data

1. Does not attempt to solve collections problems, or has syntax errors in collection code.
2. Collections methods have runtime or logic errors. Collections methods may use the wrong iterators, have incorrect logic, or many of the collections methods are unimplemented.
3. Some collections methods work correctly, though several might be unimplemented. Code may not use the appropriate built in method for each problem, or duplicate logic instead of using helper methods.
4. All collections methods are implemented and function correctly. Most use appropriate higher-level built-in methods. Methods may duplicate logic instead of using helper methods.
5. All collections methods implemented and function correctly, using appropriate higher-level built-in methods. Shared logic is factored out to helper methods.