Using Realm with Value Types

A.LICENSE.md

Copyright 2017 Guillermo Gonzalez

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

Character+Persistable.swift

import Foundation
import RealmSwift

extension Character: Persistable {

    public init(managedObject: CharacterObject) {
        identifier = managedObject.identifier
        name = managedObject.name
        realName = managedObject.realName
        publisher = managedObject.publisher.flatMap(Publisher.init(managedObject:))
    }

    public func managedObject() -> CharacterObject {
        let character = CharacterObject()

        character.identifier = identifier
        character.name = name
        character.realName = realName
        character.publisher = publisher?.managedObject()

        return character
    }
}

extension Character {

    public enum PropertyValue: PropertyValueType {
        case identifier(Int)
        case name(String)
        case realName(String)
        case publisher(Publisher?)

        public var propertyValuePair: PropertyValuePair {
            switch self {
            case .identifier(let id):
                return ("identifier", id)
            case .name(let name):
                return ("name", name)
            case .realName(let realName):
                return ("realName", realName)
            case .publisher(let publisher):
                return ("publisher", publisher?.managedObject() ?? NSNull())
            }
        }
    }
}

extension Character {

    public enum Query: QueryType {
        case publisherName(String)

        public var predicate: NSPredicate? {
            switch self {
            case .publisherName(let value):
                return NSPredicate(format: "publisher.name ==[c] %@", value)
            }
        }

        public var sortDescriptors: [SortDescriptor] {
            return [SortDescriptor(property: "name")]
        }
    }
}

Character.swift

import Foundation

public struct Character {
    public let identifier: Int
    public let name: String
    public let realName: String
    public let publisher: Publisher?
}

CharacterObject.swift

import Foundation
import RealmSwift

final public class CharacterObject: Object {
    dynamic var identifier = 0
    dynamic var name = ""
    dynamic var realName = ""
    dynamic var publisher: PublisherObject?

    override public static func primaryKey() -> String? {
        return "identifier"
    }
}

Container.swift

import Foundation
import RealmSwift

public final class Container {

    private let realm: Realm

    public convenience init() throws {
        try self.init(realm: Realm())
    }

    internal init(realm: Realm) {
        self.realm = realm
    }

    public func write(_ block: (WriteTransaction) throws -> Void) throws {
        let transaction = WriteTransaction(realm: realm)
        try realm.write {
            try block(transaction)
        }
    }

    public func values<T: Persistable> (_ type: T.Type, matching query: T.Query) -> FetchedResults<T> {
        var results = realm.objects(T.ManagedObject.self)

        if let predicate = query.predicate {
            results = results.filter(predicate)
        }

        results = results.sorted(by: query.sortDescriptors)

        return FetchedResults(results: results)
    }
}

FetchedResults.swift

import Foundation
import RealmSwift

public final class FetchedResults<T: Persistable> {

    internal let results: Results<T.ManagedObject>

    public var count: Int {
        return results.count
    }

    internal init(results: Results<T.ManagedObject>) {
        self.results = results
    }

    public func value(at index: Int) -> T {
        return T(managedObject: results[index])
    }
}

// MARK: - Collection

extension FetchedResults: Collection {

    public var startIndex: Int {
        return 0
    }

    public var endIndex: Int {
        return count
    }

    public func index(after i: Int) -> Int {
        precondition(i < endIndex)
        return i + 1
    }

    public subscript(position: Int) -> T {
        return value(at: position)
    }
}

Persistable.swift

import Foundation
import RealmSwift

/// Represents a type that can be persisted using Realm.
public protocol Persistable {

    associatedtype ManagedObject: Object
    associatedtype PropertyValue: PropertyValueType = DefaultPropertyValue
    associatedtype Query: QueryType = DefaultQuery

    init(managedObject: ManagedObject)

    func managedObject() -> ManagedObject
}

public typealias PropertyValuePair = (name: String, value: Any)

/// Represents a property value
public protocol PropertyValueType {
    var propertyValuePair: PropertyValuePair { get }
}

public enum DefaultPropertyValue: PropertyValueType {

    public var propertyValuePair: PropertyValuePair {
        return ("", 0)
    }
}

/// Represents a Query
public protocol QueryType {
    var predicate: NSPredicate? { get }
    var sortDescriptors: [SortDescriptor] { get }
}

public enum DefaultQuery: QueryType {

    public var predicate: NSPredicate? {
        return nil
    }

    public var sortDescriptors: [SortDescriptor] {
        return []
    }
}

Publisher+Persistable.swift

import Foundation

extension Publisher: Persistable {

    public init(managedObject: PublisherObject) {
        identifier = managedObject.identifier
        name = managedObject.name
    }

    public func managedObject() -> PublisherObject {
        let publisher = PublisherObject()

        publisher.identifier = identifier
        publisher.name = name

        return publisher
    }
}

Publisher.swift

import Foundation

public struct Publisher {
    public let identifier: Int
    public let name: String
}

PublisherObject.swift

import Foundation
import RealmSwift

final public class PublisherObject: Object {
    dynamic var identifier = 0
    dynamic var name = ""

    override public static func primaryKey() -> String? {
        return "identifier"
    }
}

WriteTransaction.swift

import Foundation
import RealmSwift

public final class WriteTransaction {

    private let realm: Realm

    internal init(realm: Realm) {
        self.realm = realm
    }

    public func add<T: Persistable>(_ value: T, update: Bool = false) {
        realm.add(value.managedObject(), update: update)
    }

    public func add<T: Sequence>(_ values: T, update: Bool = false) where T.Iterator.Element: Persistable {
        values.forEach { add($0, update: update) }
    }

    public func delete<T: Persistable>(_ value: T) {
        realm.delete(value.managedObject())
    }

    public func delete<T: Sequence>(_ values: T) where T.Iterator.Element: Persistable {
        realm.delete(values.map { $0.managedObject() })
    }

    public func update<T: Persistable>(_ type: T.Type, values: [T.PropertyValue]) {
        var dictionary: [String: Any] = [:]

        values.forEach {
            let pair = $0.propertyValuePair
            dictionary[pair.name] = pair.value
        }
        
        realm.create(T.ManagedObject.self, value: dictionary, update: true)
    }
}