Query interface basics in Ruby on Rails - Mini Project: Build & Apply

Query Interface Basics in Rails

📖 Scenario: You are building a simple Rails app to manage a bookstore's inventory. You want to find books based on their price and availability.

🎯 Goal: Learn how to use Rails query interface methods to filter and retrieve records from the database.

📋 What You'll Learn

Create a Book model with specific attributes

Set a price threshold variable

Use ActiveRecord query methods to find books cheaper than the threshold

Add a condition to find only books that are in stock

💡 Why This Matters

🌍 Real World

Filtering and searching records is a common task in web apps like online stores or libraries.

💼 Career

Understanding Rails query interface is essential for backend developers working with databases.

1

Create the Book model with attributes

Create a Rails model called Book with attributes title (string), price (integer), and in_stock (boolean). Then create three books with these exact values: 'Ruby Basics' priced at 30 and true for in_stock, 'Rails Advanced' priced at 50 and false for in_stock, and 'JavaScript Guide' priced at 20 and true for in_stock.

Ruby on Rails

# Define Book model and create three books with given attributes
# Your code here

Need a hint?

Use Book.create to add records with the exact attribute values.

2

Set a price threshold variable

Create a variable called max_price and set it to 40. This will be used to find books cheaper than this price.

Ruby on Rails

class Book < ApplicationRecord
end

Book.create(title: 'Ruby Basics', price: 30, in_stock: true)
Book.create(title: 'Rails Advanced', price: 50, in_stock: false)
Book.create(title: 'JavaScript Guide', price: 20, in_stock: true)

# Create max_price variable and set to 40
# Your code here

Need a hint?

Just assign the number 40 to a variable named max_price.

3

Find books cheaper than max_price

Use the Rails query interface to find all books with price less than max_price. Assign the result to a variable called cheap_books. Use where with a condition on price.

Ruby on Rails

class Book < ApplicationRecord
end

Book.create(title: 'Ruby Basics', price: 30, in_stock: true)
Book.create(title: 'Rails Advanced', price: 50, in_stock: false)
Book.create(title: 'JavaScript Guide', price: 20, in_stock: true)

max_price = 40

# Find books with price less than max_price and assign to cheap_books
# Your code here

Need a hint?

Use Book.where('price < ?', max_price) to filter books cheaper than max_price.

4

Find books cheaper than max_price and in stock

Update the query to find books with price less than max_price and in_stock equal to true. Assign the result to a variable called available_cheap_books. Use where with multiple conditions.

Ruby on Rails

class Book < ApplicationRecord
end

Book.create(title: 'Ruby Basics', price: 30, in_stock: true)
Book.create(title: 'Rails Advanced', price: 50, in_stock: false)
Book.create(title: 'JavaScript Guide', price: 20, in_stock: true)

max_price = 40

cheap_books = Book.where('price < ?', max_price)

# Find books with price less than max_price and in_stock true, assign to available_cheap_books
# Your code here

Need a hint?

Use where with SQL conditions joined by AND to filter by price and stock.