How to Write JSON in Ruby: Simple Guide with Examples

In Ruby, you can write JSON by using the JSON module from the standard library. First, require 'json', then use JSON.generate(object) or object.to_json to convert Ruby objects like hashes or arrays into JSON strings.

Syntax

To write JSON in Ruby, you need to require the json library. Then, you can convert Ruby objects to JSON strings using JSON.generate(object) or object.to_json. Both methods turn hashes, arrays, and other serializable objects into JSON format.

• require 'json': Loads the JSON library.
• JSON.generate(object): Converts a Ruby object to a JSON string.
• object.to_json: Another way to convert an object to JSON (requires require 'json').

ruby

require 'json'

ruby_hash = { name: "Alice", age: 30, city: "Wonderland" }
json_string = JSON.generate(ruby_hash)

puts json_string

Output

{"name":"Alice","age":30,"city":"Wonderland"}

Example

This example shows how to convert a Ruby hash to a JSON string and print it. It demonstrates the basic usage of JSON.generate and to_json methods.

ruby

require 'json'

person = {
  name: "Bob",
  age: 25,
  hobbies: ["reading", "cycling"]
}

# Using JSON.generate
json1 = JSON.generate(person)
puts json1

# Using to_json
json2 = person.to_json
puts json2

Output

{"name":"Bob","age":25,"hobbies":["reading","cycling"]}
{"name":"Bob","age":25,"hobbies":["reading","cycling"]}

Common Pitfalls

Common mistakes when writing JSON in Ruby include:

• Forgetting to require 'json', which causes errors when calling JSON methods.
• Trying to convert objects that are not serializable, like custom classes without to_json methods.
• Using symbols as keys in hashes without converting them, which JSON converts to strings automatically but can confuse beginners.

Always ensure your data is serializable and require 'json' is included.

ruby

require 'json'

# Wrong: forgetting to require json
# json_str = JSON.generate({a: 1}) # This will cause an error

# Right:
json_str = JSON.generate({a: 1})
puts json_str

# Wrong: trying to convert an unserializable object
class Person
  attr_accessor :name
  def initialize(name)
    @name = name
  end
end

person = Person.new("Eve")
# JSON.generate(person) # This raises an error

# Right: convert to hash first
json_str = JSON.generate({name: person.name})
puts json_str

Output

{"a":1}
{"name":"Eve"}

Quick Reference

Here is a quick summary of how to write JSON in Ruby:

Action	Code Example
Load JSON library	require 'json'
Convert hash to JSON string	JSON.generate({key: 'value'})
Convert array to JSON string	JSON.generate([1, 2, 3])
Use to_json method	{a: 1}.to_json
Print JSON string	puts JSON.generate({name: 'Alice'})

Key Takeaways

Always require 'json' before using JSON methods in Ruby.

Use JSON.generate or to_json to convert Ruby objects to JSON strings.

Make sure objects are serializable; convert custom objects to hashes first.

Symbols in hashes become strings in JSON automatically.

Common errors come from missing require or unserializable objects.