uberbruns/indexedstorage

A wrapper around Swift.Dictionary that creates and maintains multiple indices for stored Structs.

IndexedStorage

A wrapper around Swifts Dictionary type that creates and maintains multiple indices for stored Structs. You should not use it with mutable classes, because IndexedStorage will not observe properties of class instances to keep the indices up-to-date.

Install

This library should be installable via SwiftPM, Carthage and CocoaPods.

Example

Let's say you have a struct that looks like this:

struct Ship {
    let id: String
    let name: String
    let captain: String
}

1. Define Your Data Storage Subclass

To create a storage class by subclassing you need to define the Element type (Ship) and the type of the PrimaryKey you wish to use to store your data. In this case String, because we want ship.id to be the primary key. This key should be unique and Hashable.

class ShipData: IndexedStorage<Ship, String> {
}

2. Override Index Function

Our goal is to use ship.id as key for the primary index. Next, we want to maintain two additional indices for ship.name and ship.captain.

To achieve that, we need to override three functions:

2.1. Primary Key Access For The Primary Index

override class func primaryKey(for element: Ship) -> String {
    return element.id
}

2.2. Number Of Additional Indices

"2" for ship.name and ship.captain.

override class func numberOfIndices() -> Int {
    return 2
}

2.3. Hashes For The Additional Indices

By returning hashes for ship.name and ship.captain we provide all the information needed to build the additional indices. Make sure the array length equals the number returned by numberOfIndices. Otherwise the class will crash.

override class func hashValues(for element: Ship) -> [Int] {
    return [element.name.hashValue, element.captain.hashValue]
}

3. Create Convenience Accessors

You can now access structs using the additional indices by calling indexedStorage.elements(for: name, onIndex: 0). But it is more convenient to provide custom subscript functions like:

subscript(name name: String) -> [Ship] {
    return elements(for: name, onIndex: 0)
}

subscript(captain captain: String) -> [Ship] {
    return elements(for: captain, onIndex: 1)
}

4. The Final Class

class ShipData: IndexedStorage<Ship, String> {

    override class func primaryKey(for element: Ship) -> String {
        return element.id
    }

    override class func numberOfIndices() -> Int {
        return 2
    }

    override class func hashValues(for element: Ship) -> [Int] {
        return [element.name.hashValue, element.captain.hashValue]
    }

    subscript(name name: String) -> [Ship] {
        return elements(for: name, onIndex: 0)
    }

    subscript(captain captain: String) -> [Ship] {
        return elements(for: captain, onIndex: 1)
    }
}

Usage

You can now access like this:

// Add
let enterprisePike = Ship(id: "USS-1701", name: "Enterprise", captain: "Christopher Pike")
shipData.add(enterprisePike)

let enterpriseD = Ship(id: "USS-1701-D", name: "Enterprise", captain: "Jean-Luc Picard")
shipData.add(enterpriseD)

// Update
let enterpriseKirk = Ship(id: "USS-1701", name: "Enterprise", captain: "James T. Kirk")
shipData.add(enterpriseKirk) // `enterprisePike` will be replaced because of the same `id`.

// Access
shipData["USS-1701"]
// => Ship(id: "USS-1701", name: "Enterprise", captain: "James T. Kirk")

shipData[name: "Enterprise"]
// => [Ship(id: "USS-1701", name: "Enterprise", captain: "James T. Kirk"), Ship(id: "USS-1701-D", name: "Enterprise", captain: "Jean-Luc Picard")]

shipData[captain: "James T. Kirk"]
// => [Ship(id: "USS-1701", name: "Enterprise", captain: "James T. Kirk")]

// Remove
shipData.remove(enterprise)

// Remove By Primary Key
shipData.remove(key: "USS-1701")

License

This project is released under the MIT license. See LICENSE for details.