TopicController.swift

struct TopicController {
    func getTopicSubscriber(_ req: Request) throws -> Future<[User]> {
        let name = try req.parameters.next(String.self)
        guard let convert = name.removingPercentEncoding else {
            throw Abort(.expectationFailed, reason: "主题名称无效", identifier: nil)
        }
        
        return Topic.query(on: req).filter(\.name ~= convert).first().flatMap({ (topic) in
            guard let topic = topic else {
                throw Abort(.badRequest, reason: "主题不存在", identifier: nil)
            }
            
            return try topic.subcribers.query(on: req).all()
        })
    }
}