add re-usable Row<Model> class

[tanner0101]

As discussed in #11, here is a proof of concept of a generic Row type. This allows for models to just declare their unique schema, without needing to re-implement the bare-bones of a model.

Before

Before the change, properties were declared in a nested Model.Properties struct.

final class Galaxy: Model {
    struct Properties: ModelProperties {
        let id = Field<Int>("id")
        let name = Field<String>("name")
        let planets = Children<Planet>(id: .init("galaxyID"))
    }
    static let properties = Properties()
    var storage: Storage
    init(storage: Storage) {
        self.storage = storage
    }
}

let galaxy = Galaxy()
galaxy.set(\.name, to: "Milky Way")
galaxy.save()

let galaxies = db.query(Galaxy.self).filter(\.name == "Milky Way").all().wait()
print(galaxies) // [Galaxy]

After

After the change, the model is the properties struct. A method new() is available to create a Row<Model>.

struct Galaxy: Model {
    static let `default` = Galaxy()
    let id = Field<Int>("id")
    let name = Field<String>("name")
    let planets = Children<Planet>(id: .init("galaxyID"))
}

let galaxy = Galaxy.new() // Row<Galaxy>
galaxy.set(\.name, to: "Milky Way")
galaxy.save(on: db)

let galaxies = db.query(Galaxy.self).filter(\.name == "Milky Way").all().wait()
print(galaxies) // [Row<Galaxy>]

Note on dynamic KeyPath lookup

With Pitch: Key-Path Member Lookup possibly coming to Swift in the future, this change would allow us to declare Row as @keyPathMemberLookup and get back normal dot-syntax:

// with theoretical @keyPathMemberLookup 
let galaxy = Galaxy.new() // Row<Galaxy>
galaxy.name = "Milky Way"
galaxy.save(on: db)

Naming

I'm up for any ideas on how to spell Row and Model.default. Some other ideas I have:

Row:

• Ref / Reference
• Entity
• Object
• Instance

Model.default

• shared
• ref

[twof]

let galaxies = db.query(Galaxy.self).filter(\.name == "Milky Way").all()
print(galaxies) // [Instance<Galaxy>]

Should that be Future<[Instance<Galaxy>]>?

[tanner0101]

@twof oops, yeah I forgot .wait(). Added.

[twof]

With this setup, are we at risk of people using and creating initializers? Is a raw Model object useful at all?

[tanner0101]

@twof yes, it's possible people can call Planet() accidentally instead of Planet.new() and they will get a Model, not a Row<Model>. Model doesn't have any of the get / set methods though, so it should be immediately obvious that something is not right.

[tanner0101]

Seems like feedback on this change is mostly positive. Given that the changes here would likely be a requirement to supporting @dyanmicMemberLookup in the future, I think we should definitely merge. 👍

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