The summary Vapor service manufacturing unit design sample

I’ve written a number of articles about manufacturing unit design patterns on my weblog and this time I would like to speak a few particular one, which you’ll encounter in case you work with Vapor. Here is just a little recap about my manufacturing unit design sample weblog posts, all written in Swift:

Now let’s dive in to the “Fluent sample”. With a purpose to perceive this structure, first we must always look at the associated Swift packages first. There may be the FluentKit library and a number of other Fluent database driver implementations (SQLite, PostgreSQL, MySQL, and so forth.), all primarily based on the FluentKit product. Additionally there may be one bundle that connects Fluent with Vapor, this one is just referred to as: Fluent. 📀

• FluentKit – comprises the summary interface (with out Vapor, utilizing SwiftNIO)
• Fluent[xy]Driver – comprises the implementation outlined in FluentKit
• Fluent – connects FluentKit with Vapor, by extending Vapor

That is the bottom construction, the FluentKit library gives the next summary interfaces, which you must implement if you wish to create your individual driver implementation. Sadly you will not have the ability to discover correct documentation for these interfaces, so I will clarify them a bit:

• Database – Question execution and transaction associated features
• DatabaseContext – Holds the config, logger, occasion loop, historical past and web page dimension restrict
• DatabaseDriver – A manufacturing unit interface to create and shutdown Database situations
• DatabaseID – A singular ID to retailer database configs, drivers and situations
• DatabaseError – A generic database associated error protocol
• DatabaseConfiguration – A protocol to create DatabaseDriver objects
• DatabaseConfigurationFactory – A box-like object to cover driver associated stuff
• Databases – Shared config, driver and operating occasion storage

As you’ll be able to see there are various protocols concerned on this structure, however I will attempt to stroll you thru the complete driver creation movement and hopefully you can perceive how the items are associated, and the way can construct your individual drivers and even Vapor parts primarily based on this.

Fluent is written as a service for Vapor utilizing the underlying shared storage object, that is what shops a reference to the Databases occasion. This object has two hash maps, for storing configurations and operating driver situations utilizing the DatabaseID as a key for each. 🔑

While you ask for a driver, the Databases object will verify if that driver exists, if sure, it will merely return it and story over. The attention-grabbing half occurs when the driving force doesn’t exists but within the Databases storage. First the system will verify for a pre-registered driver implementation.

app.databases.use(.sqlite(.file("db.sqlite")), as: .sqlite)

This line above registers a brand new driver configuration for the shared Databases. The .sqlite() technique is a static perform on the DatabaseConfigurationFactory which creates a brand new SQLite particular configuration and hides it utilizing the init(make:) name. The SQLite associated configuration implements the DatabaseConfiguration protocol, so it may be used as a sound config when the system creates the precise database context.

The config object can be answerable for creating the precise driver object utilizing the Databases object if wanted. At this level we have got a configuration and a driver occasion registered within the databases storage. What occurs if somebody asks for a database occasion?

Relying on the context, you’ll be able to ask for a Database implementation by way of the app.db or req.db properties. That is outlined within the FluentProvider code and behind the scenes all the pieces could be traced again to the Databases class. Because you solely need to have a single shared storage for all of the drivers, however you additionally need to keep away from the singleton sample, you must hook this service as much as the Utility class. That is how the Vapor of us did it anyway. 🤓

let db: Database = req.db
let db: Database = req.db(.sqlite)

let db: Database = app.db
let db: Database = app.db(.sqlite)

While you ask for a database, or a database with an express identifier, you’re basically calling a make technique contained in the Databases class, which goes search for a registered configuration and a driver implementation utilizing the hashes and it will name the driving force’s make technique and move across the logger, the occasion loop and the present database configuration as a database context object.

We will say that after you ask for an summary Database driver, a brand new DatabaseDriver occasion reference (related to a given DatabaseID) can be saved contained in the Databases class and it will all the time make you a brand new Database reference with the present DatabaseContext. If the driving force already exists, then it will be reused, however you continue to get new Database references (with the related context) each time. So, you will need to word that there’s just one DatabaseDriver occasion per configuration / database identifier, however it will possibly create a number of Database objects. 🤔

Okay, I do know, it is fairly sophisticated, however this is an oversimplified model in Swift:

closing class Databases {
    var configs: [DatabaseID: DatabaseConfiguration] = [:]
    var drivers: [DatabaseID: DatabaseDriver] = [:]

    func make(
        _ id: DatabaseID,
        logger: Logger,
        on eventLoop: EventLoop
    ) -> Database {
        let config = configs[id]!

        if drivers[id] == nil {
            drivers[id] = config.make(self)
        }
        let context = DatabaseContext(config, logger, eventLoop)
        return drivers[id]!.make(context)
    }

    func use(_ config: DatabaseConfiguration, for id: DatabaseID) {
        configs[id] = config
    }
}

And the Vapor service extension could possibly be interpreted considerably like this:

extension Utility {

    var databases: Databases {
        get {
            if storage[DatabasesKey.self] == nil {
                storage[DatabasesKey.self] = .init()
            }
            return storage[DatabasesKey.self]
        }
        set {
            self.storage[MyConfigurationKey.self] = newValue
        }
    }

    var db: Database {
        databases.make(
            .default, 
            logger: logger, 
            eventLoop: eventLoopGroup.subsequent()
        )
    }
}

You possibly can apply the identical rules and create an extension over the Request object to entry a Database occasion. In fact there’s much more taking place below the hood, however the goal of this text is to get a primary overview of this sample, so I am not going into these particulars now. 🙃

Actually I actually like this method, as a result of it is elegant and it will possibly utterly disguise driver particular particulars by way of these abstractions. I adopted the very same rules once I created the Liquid file storage driver for Vapor and discovered lots in the course of the course of. Though, you must word that not all the pieces is an effective candidate for being applied an “summary Vapor service manufacturing unit” design sample (or no matter we name this method). Anyway, I actually hope that this fast tutorial will allow you to to create your individual Vapor parts, if wanted. 🤷‍♂️