I’ve written a number of articles about manufacturing facility design patterns on my weblog and this time I would like to speak a couple of particular one, which you’ll be able to encounter when you work with Vapor. This is a little bit recap about my manufacturing facility 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 should always look at the associated Swift packages first. There’s 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’s one package deal that connects Fluent with Vapor, this one is solely known as: Fluent. 📀
- FluentKit – incorporates the summary interface (with out Vapor, utilizing SwiftNIO)
- Fluent[xy]Driver – incorporates the implementation outlined in FluentKit
- Fluent – connects FluentKit with Vapor, by extending Vapor
That is the bottom construction, the FluentKit library offers the next summary interfaces, which it’s a must to 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 am going to clarify them a bit:
- Database – Question execution and transaction associated capabilities
- DatabaseContext – Holds the config, logger, occasion loop, historical past and web page measurement restrict
- DatabaseDriver – A manufacturing facility interface to create and shutdown Database cases
- DatabaseID – A novel ID to retailer database configs, drivers and cases
- 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 possibly can see there are a lot of protocols concerned on this structure, however I am going to attempt to stroll you thru your complete driver creation circulate and hopefully you’ll perceive how the items are associated, and the way can construct your individual drivers and even Vapor elements 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 cases utilizing the DatabaseID as a key for each. 🔑
Whenever you ask for a driver, the Databases object will examine if that driver exists, if sure, it’s going to merely return it and story over. The fascinating half occurs when the motive force doesn’t exists but within the Databases storage. First the system will examine 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() methodology is a static operate 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 legitimate config when the system creates the precise database context.
The config object can also be accountable 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 possibly can ask for a Database implementation by the app.db or req.db properties. That is outlined within the FluentProvider code and behind the scenes the whole lot will be traced again to the Databases class. Because you solely wish to have a single shared storage for all of the drivers, however you additionally wish to keep away from the singleton sample, you need to hook this service as much as the Software 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)Whenever you ask for a database, or a database with an express identifier, you might be primarily calling a make methodology contained in the Databases class, which goes search for a registered configuration and a driver implementation utilizing the hashes and it will name the motive force’s make methodology and go 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) will probably 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 motive force already exists, then it’s going to be reused, however you continue to get new Database references (with the related context) each time. So, it is very important be aware that there’s just one DatabaseDriver occasion per configuration / database identifier, however it might probably create a number of Database objects. 🤔
Okay, I do know, it is fairly sophisticated, however here 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 may very well be interpreted considerably like this:
extension Software {
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’ll be able to apply the identical rules and create an extension over the Request object to entry a Database occasion. In fact there’s much more occurring beneath the hood, however the goal of this text is to get a fundamental overview of this sample, so I am not going into these particulars now. 🙃
Truthfully I actually like this strategy, as a result of it is elegant and it might probably fully disguise driver particular particulars by these abstractions. I adopted the very same rules once I created the Liquid file storage driver for Vapor and realized so much throughout the course of. Though, you need to be aware that not the whole lot is an effective candidate for being carried out an “summary Vapor service manufacturing facility” design sample (or no matter we name this strategy). Anyway, I actually hope that this fast tutorial will assist you to create your individual Vapor elements, if wanted. 🤷♂️