Papyrus

Papyrus enables offline first applications by providing a simple object cache layer.

Simple example

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()
try await store.save(car)

Realworld example

In this example, we're using a AsyncThrowingStream to pump through values.

The general concept is that firstly we yield the cached data, perform the API request, yield the new objects and finally merge the new cached objects.

import AsyncAlgorithms
import Papyrus

struct CarProvider {
    var all: () -> AsyncThrowingStream<[Car], Error>
}

extension CarProvider {
    static func live(
        apiClient: TeslaAPIClient = .live,
        store: PapyrusStore = .live
    ) -> Self {
        .init(
            all: {
                AsyncThrowingStream { continuation in
                    do {
                        var stores = store.objects(type: Car.self).execute()
                        continuation.yield(stores)
                        
                        let request = FetchCarsRequest()
                        cars = try await apiClient.execute(request: request)
                        continuation.yield(cars)
                        try await store.merge(with: cars)
                        continuation.finish()
                    } catch {
                        continuation.finish(throwing: error)
                    }
                }
                .removeDuplicates()
                .eraseToThrowingStream()
            }
        )
    }
}

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()
try await store.save(car)

Example B - 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()
try await store.save(objects: [carA, carB])

try await store.merge(with: [carA, carC])
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 = store.object(id: "abc...", of: Manufacturer.self).execute()

Example B

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 = 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

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)
try store.delete(tesla)

Example B

let store = PapyrusStore()
try 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)
try store.delete(objects: [tesla, ford])