Papyrus

Papyrus aims to hit the sweet spot between saving raw API responses to the file system and a fully fledged database like Realm.

struct Car: Papyrus {
    let id: String
    let model: String
    let manufacturer: String
}

let car = Car(id: "abc...", model: "Model S", manufacturer: "Tesla")
let store = PapyrusStore()
await store.save(car)

Requirements

• iOS 15.0+
• macOS 12.0+
• watchOS 6.0+
• tvOS 15.0+

Installation

Swift Package Manager

In Xcode:

1. Click Project.
2. Click Package Dependencies.
3. Click +.
4. Enter package URL: https://github.com/reddavis/Papyrus.
5. Add Papyrus to your app target.

Documentation

API Reference

Usage

Saving

Anything that conforms to the Papyrus protocol can be stored.

The Papyrus protocol is simply an umbrella of these three protocols:

• Codable
• Equatable
• Identifiable where ID: LosslessStringConvertible

Example A

struct Car: Papyrus {
    let id: String
    let model: String
    let manufacturer: String
}

let car = Car(id: "abc...", model: "Model S", manufacturer: "Tesla")
let store = PapyrusStore()
await store.save(car)

Example B - Relationships

Papyrus also understands relationships. If we continue with our Car modelling...Let's imagine we have an app that fetches a list of car manufacturers and their cars.

Our models could look like:

struct Manufacturer: Papyrus {
    let id: String
    let name: String
    @HasMany let cars: [Car]
    @HasOne let address: Address
}

struct Car: Papyrus {
    let id: String
    let model: String
}

struct Address: Papyrus {
    let id: UUID
    let lineOne: String
    let lineTwo: String?
}

let modelS = Car(id: "abc...", model: "Model S")
let address = Address(id: UUID(), lineOne: "blah blah", lineTwo: nil)
let tesla = Manufacturer(
    id: "abc...", 
    name: "Tesla", 
    cars: [modelS], 
    address: address
)

let store = PapyrusStore()
await store.save(tesla)

Because Car and Address also conforms to Papyrus and the @HasMany and @HasOne property wrappers have been used, PapyrusStore will also persist the cars and the address when it saves the manufacturer. This means that we are able to perform direct queries on Car's and Addresses.

Example C - Merge

A common use case when dealing with API's is to fetch a collection of objects and the merge the results into your local collection.

Papyrus provides a function for this:

let carA = Car(id: "abc...", model: "Model S", manufacturer: "Tesla")
let carB = Car(id: "def...", model: "Model 3", manufacturer: "Tesla")
let carC = Car(id: "ghi...", model: "Model X", manufacturer: "Tesla")

let store = PapyrusStore()
store.save(objects: [carA, carB])

await store.merge(with: [carA, carC])
await store
    .objects(type: Car.self)
    .execute()
// #=> [carA, carC]

Fetching by ID

Fetching objects has two forms:

• Fetch by id.
• Fetch collection.

Example A

let store = PapyrusStore()
let tesla = try await store.object(id: "abc...", of: Manufacturer.self).execute()

Example B

You also have the option of a Publisher that will fire an event on first fetch and then when the object changes or is deleted.

When the object doesn't exist a PapyrusStore.QueryError error is sent.

let store = PapyrusStore()
let cancellable = store.object(id: "abc...", of: Manufacturer.self)
    .publisher()
    .sink(
        receiveCompletion: { ... },
        receiveValue: { ... }
    )

Example C

With Swift 5.5 came async/await, which also introduced AsyncSequence.

When the object doesn't exist a PapyrusStore.QueryError error is thrown.

let store = PapyrusStore()
let stream = store.object(id: "abc...", of: Manufacturer.self).stream()

do {
    for try await object in stream {
        ...
    }
} catch {
    //.. Do something
}

Fetching collections

Papryrus gives you the ability to fetch, filter and observe colletions of objects.

Example A - Simple fetch

let manufacturers = await self.store
    .objects(type: Manufacturer.self)
    .execute()

Example B - Filtering

let manufacturers = await self.store
    .objects(type: Manufacturer.self)
    .filter { $0.name == "Tesla" }
    .execute()

Example C - Sorting

let manufacturers = await self.store
    .objects(type: Manufacturer.self)
    .sort { $0.name < $1.name }
    .execute()

Example D - Observing changes with Combine

Calling publisher() on a PapryrusStore.CollectionQuery object will return a Combine publisher which will emit the collection of objects. Unless specified the publisher will continue to emit a collection objects whenever a change is detected.

A change constitutes of:

• Addition of an object.
• Deletion of an object.
• Update of an object.

self.store
    .objects(type: Manufacturer.self)
    .publisher()
    .subscribe(on: DispatchQueue.global())
    .receive(on: DispatchQueue.main)
    .sink { self.updateUI(with: $0) }
    .store(in: &self.cancellables)

Example E - All together

self.store
    .objects(type: Manufacturer.self)
    .filter { $0.name == "Tesla" }
    .sort { $0.name < $1.name }
    .publisher()
    .subscribe(on: DispatchQueue.global())
    .receive(on: DispatchQueue.main)
    .sink { self.updateUI(with: $0) }
    .store(in: &self.cancellables)

Example F - Observing changes with a stream

Calling stream() on a PapryrusStore.CollectionQuery object will return a AsyncThrowingStream which will emit the collection of objects. Unless specified the stream will continue to emit a collection objects whenever a change is detected.

A change constitutes of:

• Addition of an object.
• Deletion of an object.
• Update of an object.

let stream = self.store
    .objects(type: Manufacturer.self)
    .filter { $0.name == "Tesla" }
    .sort { $0.name < $1.name }
    .stream()

do {
    for try await manufacturers in stream {
        // ... Do something with [Manufacturer].
    }
} catch {
    //.. Do something
}

Deleting

There are several methods for deleting objects.

Example A

let store = PapyrusStore()
let tesla = store.object(id: "abc...", of: Manufacturer.self)
await store.delete(tesla)

Example B

let store = PapyrusStore()
await store.delete(id: "abc...", of: Manufacturer.self)

Example C

let store = PapyrusStore()
let tesla = store.object(id: "abc...", of: Manufacturer.self)
let ford = store.object(id: "xyz...", of: Manufacturer.self)
await store.delete(objects: [tesla, ford])

Migrations (experimental)

If the wish is to keep existing data when introducing schema changes you can register a migration.

Example A

struct Car: Papyrus {
    let id: String
    let model: String
    let manufacturer: String
}

struct CarV2: Papyrus {
    let id: String
    let model: String
    let manufacturer: String
    let year: Int
}

let migration = Migration<Car, CarV2> { oldObject in
    CarV2(
        id: oldObject.id,
        model: oldObject.model,
        manufacturer: oldObject.manufacturer,
        year: 0
    )
}

await self.store.register(migration: migration)