MongoDB object persistence for Swift
Meow is a boilerplate-free object persistence framework for Swift and MongoDB, from the creators of MongoKitten.
It manages your database for you, so you can focus on writing your application.
For users of Vapor 4 and/or NIO 2.x, Meow is now available as a very lightweight layer as part of the MongoKitten repository.
Meow has a type Manager that manages the database for you. You’ll need one per NIO event loop. The manager is a small wrapper around MongoKitten which takes care of connecting, discovery and reconnecting.
From your manager you can create a Context, think of a context as something that is relevant within a single task. A task might be running migrations or responding to an HTTP request.
Within your Context, models are cached and references. So if you fetch the same user twice, Meow will refer back to the original instance the second time as long as it’s available within the current Context. It’s strongly encouraged to resolve references that rely on this mechanism.
When creating a Model you need to conform your class to Model.
The only requirement is that you add a property to your model with a key of _id and is not a computed property.
final class User: Model {
var _id = ObjectId()
...
}
You can use any type for the _id key as long as it’s a standard BSON Primitive type including:
Binary / DataThe following is completely legitimate:
// Stores the username in _id
final class User: Model {
var _id: String
var username: String {
return _id
}
...
By default the model name will be used for the collection name. You can customize this with a static let collectionName: String
final class User: Model {
// Changes the collection name from `User` to `users`
static let collectionName = "users"
var _id = ObjectId()
...
Queries reside within the Context.
final class Article: Model {
var _id = ObjectId()
let creator: Reference<User>
var title: String
var text: String
...
The above demonstrates how a simple reference can be created to another model. In this case a User model. And below demonstrates resolving the reference.
let resolvedUser = article.creator.resolve(in: context)
The result in this case is an EventLoopFuture<User>, but if you wish to resolve the reference’s target to nil if it doesn’t exist you can simply do article.creator.resolveIfPresent(in: context).
You’re also able to delete the target of the reference using reference.deleteTarget(in: context). This implies that resolving the normal way (not with ifPresent) will result in a failure.
If a feature is unsupported by Meow, for example when it can’t be type-safe, you can always fall back to MongoKitten.
let database: MongoKitten.Database = context.manager.database
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