/orm-mapping-db-to-ruby-object-lab-online-web-pt-071519

Primary LanguageRubyOtherNOASSERTION

ORM Mapping Database Rows to Ruby Objects

Objectives

  • Write a method that turns database rows into Ruby objects
  • Write methods that allow you to search a database

Overview

We are going to continue building out the Student class of our app. We are in the middle of building an app to help a public school's administrators keep track of their students. In this app, we have a Student class. Each individual student has two attributes, a name and a grade, i.e. 9th, 10th, 11th, etc.

Our administrators need to save the student objects that this class produces to a database. We've set up the database for you in the config/environment.rb file.

Let's take a look:

require 'sqlite3'
require_relative '../lib/student'

DB = {:conn => SQLite3::Database.new("db/students.db")}

Your connection to the database can be referred to, throughout your program, like this: DB[:conn].

So far we built the ability to create the students table in the database (Student.create_table), drop that table (Student.drop_table), and #save a student to the database.

Now, we will need to create a method that takes a row from the database and turns it back into a Student object. We will call this .new_from_db.

Next, we want to build a couple of methods to get information from the database. We will call these .find_by_name and .all.

Let's get started!

Instructions

The .new_from_db Method

This is a class method that accepts a row from the database as an argument. It then creates a new student object based on the information in the row. Remember, our database doesn't store Ruby objects, so we have to manually convert it ourselves.

The .find_by_name Method

This is a class method that accepts the name of a student. You will first run a SQL query to get the result from the database where the student's name matches the name passed into the argument.

Next, you will take the result and create a new student instance using the .new_from_db method you just created.

The .all Method

This is a class method that is very similar to the .find_by_name method. You will not need an argument since we are returning everything in the database. Run the SQL to return everything (*) from a table.

Again, you will use the .new_from_db method to create a student instance for each row that comes back from the database.

The .all_students_in_grade_9 Method

This is a class method that does not need an argument. This method should return an array of all the students in grade 9.

The .students_below_12th_grade Method

This is a class method that does not need an argument. This method should return an array of all the students below 12th grade.

The .first_X_students_in_grade_10 Method

This is a class method that takes in an argument of the number of students from grade 10 to select. This method should return an array of exactly X number of students.

The .first_student_in_grade_10 Method

This is a class method that does not need an argument. This should return the first student that is in grade 10.

The .all_students_in_grade_X Method

This is a class method that takes in an argument of a grade for which to retrieve the roster. This method should return an array of all students for grade X.

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