gistfile1.txt

// Playground - noun: a place where people can play

import UIKit
import XCPlayground

protocol ObjectProtocol {}


protocol QuerySetProtocol {
}

class QuerySetJoining<Q: QuerySetProtocol> {
    
    let query: Q
    
    init(query: Q) {
        self.query = query
    }
    
    func on<Lhs: AttributeProtocol, Rhs: AttributeProtocol where Lhs.Element == Rhs.Owner>(lhs: Lhs, with rhs: Rhs) -> Q {
        return query
    }
    
    func on<Lhs: AttributeProtocol, Rhs: AttributeProtocol where Lhs.Owner == Rhs.Element>(lhs: Lhs, with rhs: Rhs) -> Q {
        return query
    }
}

extension QuerySetProtocol {
    
    func filter(p: NSPredicate) -> Self {
        
        return self
    }
    
    func join<O: ObjectProtocol>(o: O.Type) -> QuerySetJoining<Self> {
        return QuerySetJoining(query: self)
    }
    
}

extension QuerySetProtocol where Self: Select {
    
    func from<O: ObjectProtocol>(o: O.Type) -> Self {
        return self
    }
}



class Select: QuerySetProtocol {
    
    let keys: [String]
    
    init(_ keys: String...) {
        self.keys = keys
    }
    
}

class Update<O: ObjectProtocol>: QuerySetProtocol {
    
    func set<Attribute: AttributeProtocol where Attribute.Owner == O>(attr: Attribute, _ val: Attribute.Element) -> Self {
        return self
    }
}


class User: ObjectProtocol {
    
    var name: String = ""
    
    static let id = Attribute<Int, User>("id")
    static let name = Attribute<String, User>("name")
}

class Photo: ObjectProtocol {
    
    static let id = Attribute<Int, Photo>("id")
    static let user_id = Attribute<User, Photo>("user_id")
}

protocol AttributeProtocol {
    typealias Element
    typealias Owner
}

final class Attribute<E, O: ObjectProtocol>: AttributeProtocol {
    
    typealias Element = E
    typealias Owner = O
    
    let key: String
    
    init(_ key: String) {
        self.key = key
    }
    
    func val(val: Element) -> Self {
        
        return self
    }
}

func == <Element, Owner>(lhs: Attribute<Element, Owner>, rhs: Element) -> NSPredicate {
    return NSPredicate(value: true)
}


Select().from(User).join(Photo).on(Photo.user_id, with: User.id).filter(User.name == "test")
Select().from(User).join(Photo).on(User.id, with: Photo.user_id).filter(User.name == "test")

Update<User>()
    .set(User.name, "")
    .set(User.id, 2)
    .filter(User.name == "test")