Builder Pattern

Builder.swift

import Vapor
import Foundation
import FluentProvider

protocol Builder {
    
    associatedtype T
    
    typealias BuilderClosure = (Self) -> ()
    
    init()
    
    static func build(buildClosure: BuilderClosure?) -> T
    func build(buildClosure: BuilderClosure?) -> T
    
    func finish() -> T
}

extension Builder {
    static func build(buildClosure: BuilderClosure? = nil) -> T {
        return Self().build(buildClosure: buildClosure)
    }
    func build(buildClosure: BuilderClosure? = nil) -> T {
        buildClosure?(self)
        return finish()
    }
}

Builders.swift

import Vapor
import Foundation
import FluentProvider

final class UserBuilder: Builder {
    
    typealias T = User
    
    func uniqueUsername() {
        self.username = UUID().uuidString
    }

    var username: String = "anyUsername"
    var password: String = "anyPassword"

    func finish() -> User {
        let user = User(name: username, password: password)
        
        return user
    }
}

final class TeamBuilder: Builder {
    
    typealias T = Team
    
    var name: String = "anyName"
    
    func finish() -> Team {
        return Team(name: name)
    }
}

final class TeamMembershipBuilder: Builder {
    
    typealias T = TeamMembership?
    
    var userid: Identifier?
    var teamid: Identifier?
    
    func finish() -> TeamMembership? {
        if let userid = userid, let teamid = teamid {
            return TeamMembership(teamid: teamid, userid: userid)
        }
        
        return nil
    }
}

final class RoleBuilder: Builder {
    
    typealias T = Role
    
    var name: String = "anyName"
    var readableName: String = "anyReadableName"
    
    func finish() -> Role {
        return Role(name: name, readableName: readableName)
    }
}

final class RoleAssignmentBuilder: Builder {
    
    typealias T = RoleAssignment?
    
    var userid: Identifier?
    var roleid: Identifier?
    
    func finish() -> RoleAssignment? {
        if let userid = userid, let roleid = roleid {
            return RoleAssignment(roleid: roleid, userid: userid)
        }
        
        return nil
    }
}

BuildersExamples.swift

let user = UserBuilder.build {
    $0.username = "testUser"
    $0.password = "password"
}
try user.save()

let team = TeamBuilder.build {
    $0.name = name
}
try team.save()

let membership = TeamMembershipBuilder.build {
    $0.teamid = team.id
    $0.userid = user.id
}
try membership.save()

let role = RoleBuilder.build {
    $0.name = "admin"
    $0.readableName = "Administrator"
}
try role.save()

let assignment = RoleAssignmentBuilder.build {
    $0.roleid = role.id
    $0.userid = user.id
}
try assignment.save()