Generating a Unique Identifier with UUID

Generating a unique identifier is easy thanks to Foundation's UUID struct. In this episode of Swift Fundamentals, you learn how to create an identifier that is (almost) guaranteed to be unique.

Creating a Unique Identifier

There are plenty of scenarios in which you need a unique identifier. I typically generated a unique identifier for Core Data records to avoid conflicts on the backend. Let me show you how that works.

The start of the story is the UUID struct. This type was introduced many years ago and has made it trivial to address this common need. Fire up Xcode and create a playground by choosing the Blank template from the iOS > Playground section if you want to follow along.

Add an import statement for Foundation because the UUID struct is defined in Foundation. We create a UUID object.

import Foundation

let uuid = UUID()

In most use cases, you need the UUID as a string, for example, if you send the UUID to a server. You can access the string representation of the UUID object through its uuidString property.

import Foundation

let uuid = UUID()
uuid.uuidString // E0B1B7FD-61A8-49F1-8729-B628D42396D4

The UUID (universally unique identifier) conforms to RFC 4122, and you are unlikely to ever create the same UUID. That's the idea underlying the UUID struct.

Core Data

A few years ago, Apple added support for UUIDs to Core Data. You can set the type of an attribute to UUID in Core Data's data model editor.

Remember that a Core Data attribute of type UUID corresponds to a property of type UUID. The UUID isn't of type String.

Encoding and Decoding

The good news is that the UUID struct conforms to the Encodable and Decodable protocols, Codable for short. It is trivial to convert an object with a property of type UUID to, for example, JSON.

import Foundation

struct Book: Codable {

    // MARK: - Properties

    let uuid: UUID
    let title: String

}

let book = Book(
    uuid: UUID(),
    title: "The Hobbit"
)

If we encode the Book object to JSON using a JSONEncoder instance, the UUID object is converted to a String.

{
  "uuid": "7B4F7C20-4127-444C-A168-F4A1A88C2213",
  "title": "The Hobbit"
}

Converting the UUID from a string is also supported thanks to an initializer that accepts a string as an argument.

let uuidAsString = "E0B1B7FD-61A8-49F1-8729-B628D42396D4"
let uuid = UUID(uuidString: uuidAsString)

What's Next?

The UUID struct is a nice, little helper that does a few things, but it does them very well. It avoids the need to develop your own implementation to generate unique identifiers or rely on a third party solution.