Keep your models synchronized in your app and never have any inconsistency anymore. Designed using latest Swift features.
- 🔁 You need realtime synchronisation (websockets)
- 🌐 You have multiple data sources (REST, CoreData, websocket, phone Contacts, Google Maps, etc...)
- 🪶 You look for a full Swift lightweight tool
- 🗃️ You want to use structs
- 🦺 Thread safe
- 🪶 Lighweight (< 600 lines of code)
- 🪪 Working with plain Swift
struct
andIdentifiable
objects - 🔀 Support for Combine
- 🧠 In-memory storage
- 🐾 Low memory footprint
- 🐪 Strongly typed
CohesionKit being a Single Source of Truth solution it handles your objects lifecycle and synchronization from any source.
You should put CohesionKit in front of your data sources (REST API, GraphQL, ...) before returning data to your app.
sequenceDiagram
autonumber
YourApp ->>DataSource: findBooks
DataSource ->>GraphQL: query findBooks
GraphQL -->>DataSource: FindBooksQueryResult
DataSource ->>CohesionKit: store books [A,B,C]
CohesionKit -->> YourApp: Publisher<[A,B,C]>
WebSocket ->> WebSocketListener: book A updated
WebSocketListener ->> CohesionKit: update book A
CohesionKit -->> YourApp: Publisher<[A,B,C]>
- Swift Package Manager
dependencies: [
.package(url: "https://github.com/pjechris/CohesionKit.git", .upToNextMajor(from: "0.7.0"))
]
Library comes with an example project so you can see a real case usage. It mostly shows:
- How to store data in the library
- How to retrieve and update that data for realtime
- How data is synchronised throughout multiple screens
First create an instance of IdentityMap
:
let identityMap = IdentityMap()
IdentityMap
let you store Identifiable
objects:
struct Book: Identifiable {
let id: String
let title: String
}
let book = Book(id: "ABCD", name: "My Book")
identityMap.store(book)
Then You can retrieve the object from anywhere in your code:
// somewhere else in the code
identityMap.find(Book.self, id: "ABCD") // return Book(id: "ABCD", name: "My Book")
Every time data is updated in IdentityMap
triggers a notification to any registered observer. To register yourself as an observer just use result from store
or find
methods:
func findBooks() -> some Publisher<[Book], Error> {
// 1. load data using URLSession
URLSession(...)
// 2. store data inside our identityMap
.store(in: identityMap)
.sink { ... }
.store(in: &cancellables)
}
identityMap.find(Book.self, id: 1)?
.asPublisher
.sink { ... }
.store(in: &cancellables)
CohesionKit has a weak memory policy you should read about. As such, returned value from identityMap.store must be strongly retained to not lose value.
For brievety, next examples will omit
.sink { ... }.store(in:&cancellables)
.
To store objects containing nested identity objects you need to make them conform to one protocol: Aggregate
.
struct AuthorBooks: Aggregate {
var id: Author.ID { author.id }
let author: Author
let books: [Book]
// `nestedEntitiesKeyPaths` must list all Identifiable/Aggregate this object contain
var nestedEntitiesKeyPaths: [PartialIdentifiableKeyPath<Self>] {
[.init(\.author), .init(\.books)]
}
}
CohesionKit then handles synchronisation for the three entities:
- AuthorBook
- Author
- Book
This gives you the ability to retrieve them independently from each other:
let authorBooks = AuthorBooks(
author: Author(id: 1, name: "George R.R Martin"),
books: [
Book(id: "ACK", title: "A Clash of Kings"),
Book(id: "ADD", title: "A Dance with Dragons")
]
)
identityMap.store(authorBooks)
identityMap.find(Author.self, id: 1) // George R.R Martin
identityMap.find(Book.self, id: "ACK") // A Clash of Kings
identityMap.find(Book.self, id: "ADD") // A Dance with Dragons
You can also modify any of them however you want. Notice the change is visible from the object itself AND from aggregate objects:
let newAuthor = Author(id: 1, name: "George R.R MartinI")
identityMap.store(newAuthor)
identityMap.find(Author.self, id: 1) // George R.R MartinI
identityMap.find(AuthorBooks.self, id: 1) // George R.R MartinI [A Clash of Kings, A Dance with Dragons]
You might think about storing books on
Author
directly (author.books
). In this caseAuthor
needs to implementAggregate
and declarebooks
as nested entity.However I strongly advise you to not nest
Identifiable
objects into otherIdentifiable
objects. Read Handling relationships article if you want to know more about this subject.
For now we only focused on identityMap.store
but CohesionKit comes with another method to store data: identityMap.update
.
Sometimes both can be used but they each have a different purpose:
store
is suited for storing full data retrieved from webservices, likeGET /user
for instanceupdate
is usually used for partial data. It's also the preferred method when receiving events from websockets.
Sometimes you need to retrieve data without knowing the object id. Common case is current user.
CohesionKit provides a suitable mechanism: aliases. Aliases allow you to register and find entities using a key.
extension AliasKey where T == User {
static let currentUser = AliasKey("user")
}
identityMap.store(currentUser, named: .currentUser)
Then request it somewhere else:
identityMap.find(named: .currentUser) // return the current user
Compared to regular entities, aliased objects are long-live objects: they will be kept in the storage even if no one observes them. This allow registered observers to be notified when alias value change:
identityMap.removeAlias(named: .currentUser) // observers will be notified currentUser is nil.
identityMap.store(newCurrentUser, named: .currentUser) // observers will be notified that currentUser changed even if currentUser was nil before
When storing data CohesionKit actually require you to set a modification stamp on it. Stamp
is used as a marker to compare data freshness: the higher stamp is the more recent data is.
By default CohesionKit will use the current date as stamp.
identityMap.store(book) // use default stamp: current date
identityMap.store(book, modifiedAt: Date().stamp) // explicitly use Date time stamp
identityMap.store(book, modifiedAt: 9500) // any Double value is valid
If for some reason you try to store data with a stamp lower than the already stamped stored data then the update will be discarded.
CohesionKit has a weak memory policy: objects are kept in IdentityMap
as long as someone use them.
To that end you need to retain observers as long as you're interested in the data:
let book = Book(id: "ACK", title: "A Clash of Kings")
let cancellable = identityMap.store(book) // observer is retained: data is retained
identityMap.find(Book.self, id: "ACK") // return "A Clash of Kings"
If you don't create/retain observers then once entities have no more observers they will be automatically discarded from the storage.
let book = Book(id: "ACK", title: "A Clash of Kings")
_ = identityMap.store(book) // observer is not retained and no one else observe this book: data is released
identityMap.find(Book.self, id: "ACK") // return nil
let book = Book(id: "ACK", title: "A Clash of Kings")
var cancellable = identityMap.store(book).asPublisher.sink { ... }
let cancellable2 = identityMap.find(Book.self, id: "ACK") // return a publisher
cancellable = nil
identityMap.find(Book.self, id: "ACK") // return "A Clash of Kings" because cancellable2 still observe this book
Let's say you have an enum with Identifiable
/Aggregate
:
enum MediaType: Identifiable {
case book(Book)
case game(Game)
case tvShow(TvShow)
}
struct AuthorMedia: Aggregate {
let author: Author
let media: [MediaType]
}
let lastOfUsPart1 = Game(id: xx, title: "The Last Of Us", supportedPlatforms: [.ps3, .ps4])
let lastOfUs = TvShow(title: "The Last Of Us", releasedYear: 2023)
let naughtyDog = Author(
author: .naughtyDog,
media: [.game(theLastOfUsPart1), .movie(theLastOfUst)]
)
identityMap.store(naughtyDog)
If associated value changes you might need to do a double update inside the lib in order to properly propagate the modifications:
let lastOfUsPart1 = Game(id: xx, title: "The Last Of Us", supportedPlatforms: [.ps3, .ps4, .ps5, .pc])
identityMap.store(lastOfUsPart1) // this only notifies objects direct Game reference, not objects using MovieType.game (like our previous `naughtyDog`)
identityMap.store(MovieType.game(lastOfUsPart1)) // on the other hand this one notifies objects like naughtyDog but not those using a plain Game
Note that in this context CohesionKit stores the value twice: once as Game
and once as MediaType.game
hence the double update.
This project is released under the MIT License. Please see the LICENSE file for details.