JSON library basics in Ruby - Mini Project: Build & Apply

JSON library basics

📖 Scenario: You are working on a small Ruby program that needs to handle data in JSON format. JSON is a common way to store and share data, like a list of items with details.

🎯 Goal: You will create a Ruby program that uses the JSON library to convert a Ruby hash into a JSON string and then print it.

📋 What You'll Learn

Use the Ruby JSON library

Create a Ruby hash with specific key-value pairs

Convert the hash to a JSON string

Print the JSON string

💡 Why This Matters

🌍 Real World

JSON is used everywhere to send data between web browsers and servers, or to save data in files. Knowing how to convert Ruby data to JSON helps you work with APIs and web services.

💼 Career

Many programming jobs require working with JSON data. This skill is essential for backend development, web development, and data processing roles.

1

Create a Ruby hash with data

Create a Ruby hash called person with these exact key-value pairs: "name" => "Alice", "age" => 30, and "city" => "New York".

Ruby

# Create the hash called person with the given keys and values
# Your code here

Hint

Use curly braces {} to create a hash. Use strings as keys and values as shown.

2

Require the JSON library

Add a line to require the Ruby json library at the top of your code.

Ruby

# Require the JSON library
# Your code here

person = {"name" => "Alice", "age" => 30, "city" => "New York"}

Hint

Use require 'json' to load the JSON library.

3

Convert the hash to a JSON string

Create a variable called json_string and set it to the JSON string version of the person hash using JSON.generate(person).

Ruby

require 'json'

person = {"name" => "Alice", "age" => 30, "city" => "New York"}

# Convert person hash to JSON string and store in json_string
# Your code here

Hint

Use JSON.generate to convert a Ruby hash to a JSON string.

4

Print the JSON string

Write a line to print the json_string variable.

Ruby

require 'json'

person = {"name" => "Alice", "age" => 30, "city" => "New York"}

json_string = JSON.generate(person)

# Print the JSON string
# Your code here

Hint

Use puts to print the JSON string.

Practice

1.

What does the Ruby JSON.parse method do?

easy

A. Reads a file from disk

B. Converts a Ruby object into a JSON string

C. Converts a JSON string into a Ruby object

D. Writes a JSON string to a file

Solution

1. Step 1: Understand JSON.parse purpose

   The method JSON.parse reads a JSON formatted string and converts it into a Ruby data structure like a hash or array.

2. Step 2: Compare with other JSON methods

   JSON.generate does the opposite by converting Ruby objects into JSON strings.

3. Final Answer:

   Converts a JSON string into a Ruby object -> Option C

4. Quick Check:

   JSON.parse = JSON string to Ruby object [OK]

Hint: Remember: parse means read JSON into Ruby [OK]

Common Mistakes:

• Confusing parse with generate
• Thinking parse writes files
• Assuming parse converts Ruby to JSON

2.

Which of the following is the correct way to convert a Ruby hash {"name" => "Alice"} to a JSON string?

easy

A. JSON.generate({"name" => "Alice"})

B. JSON.dump({"name" => "Alice"}, $stdout)

C. JSON.load({"name" => "Alice"})

D. JSON.parse({"name" => "Alice"})

Solution

1. Step 1: Identify method to convert Ruby object to JSON string

   JSON.generate converts Ruby objects like hashes into JSON strings.

2. Step 2: Check other methods

   JSON.parse reads JSON strings, JSON.load is similar to parse but less common, JSON.dump also converts Ruby objects but requires a string or IO target.

3. Final Answer:

   JSON.generate({"name" => "Alice"}) -> Option A

4. Quick Check:

   generate = Ruby object to JSON string [OK]

Hint: Use generate to make JSON strings from Ruby hashes [OK]

Common Mistakes:

• Using parse instead of generate
• Confusing dump with parse
• Passing Ruby hash directly to parse

3.

What is the output of this Ruby code?

require 'json'
json_str = '{"age":30,"city":"NY"}'
ruby_obj = JSON.parse(json_str)
puts ruby_obj["city"]

medium

A. SyntaxError

B. 30

C. nil

D. NY

Solution

1. Step 1: Parse JSON string into Ruby hash

   The string {"age":30,"city":"NY"} is parsed into a Ruby hash with keys "age" and "city".

2. Step 2: Access the value for key "city"

   Using ruby_obj["city"] returns the string "NY".

3. Final Answer:

   NY -> Option D

4. Quick Check:

   JSON.parse + key access = value [OK]

Hint: Parse JSON then access keys like a hash [OK]

Common Mistakes:

• Expecting numeric output instead of string
• Using symbol keys instead of string keys
• Forgetting to require 'json'

4.

Identify the error in this Ruby code snippet:

require 'json'
json_str = '{"name": "Bob", "age": 25}'
ruby_obj = JSON.generate(json_str)
puts ruby_obj

medium

A. Using JSON.generate on a JSON string instead of a Ruby object

B. Missing require 'json' statement

C. Incorrect JSON string format

D. Using puts instead of print

Solution

1. Step 1: Check method usage

   JSON.generate expects a Ruby object (like a hash), but here it is given a JSON string.

2. Step 2: Understand correct usage

   To convert JSON string to Ruby object, use JSON.parse. To convert Ruby object to JSON string, use JSON.generate.

3. Final Answer:

   Using JSON.generate on a JSON string instead of a Ruby object -> Option A

4. Quick Check:

   generate needs Ruby object, not JSON string [OK]

Hint: Use parse for strings, generate for Ruby objects [OK]

Common Mistakes:

• Confusing generate and parse
• Passing string to generate
• Ignoring error messages

5.

You have a Ruby array [1, 2, 3]. You want to convert it to a JSON string and then back to a Ruby array. Which sequence of methods correctly does this?

hard

A. JSON.dump(JSON.parse([1, 2, 3]))

B. JSON.load(JSON.dump([1, 2, 3]))

C. JSON.generate(JSON.parse([1, 2, 3]))

D. JSON.dump(JSON.load([1, 2, 3]))

Solution

1. Step 1: Convert Ruby array to JSON string

   JSON.dump([1, 2, 3]) converts the Ruby array into a JSON string.

2. Step 2: Convert JSON string back to Ruby array

   JSON.load reads the JSON string and returns the Ruby array.

3. Step 3: Verify other options

   JSON.dump(JSON.parse([1, 2, 3])) tries to parse a Ruby array (invalid); JSON.generate(JSON.parse([1, 2, 3])) tries to parse a Ruby array (invalid); JSON.dump(JSON.load([1, 2, 3])) tries to load a Ruby array (invalid).

4. Final Answer:

   JSON.load(JSON.dump([1, 2, 3])) -> Option B

5. Quick Check:

   dump then load = Ruby array round-trip [OK]

Hint: Use dump then load for Ruby object to JSON and back [OK]

Common Mistakes:

• Parsing Ruby objects instead of JSON strings
• Using generate with parse incorrectly
• Confusing dump/load with generate/parse