swift-microservices/swift-persistence

The boundary

public protocol Database<Scope>: Sendable {
    associatedtype Scope: Sendable

    func withTransaction<T: Sendable>(
        _ operation: @Sendable (Scope) async throws -> T
    ) async throws -> T
}

When the closure returns, the transaction commits. When it throws, the transaction rolls back and the same error reaches the caller: no wrapper, so a use case catches the domain error its repository raised.

The scope

The Scope is what the closure receives: repositories built on the transaction's connection, so everything inside the closure shares one transaction.

A use case declares the scope it needs as a protocol and takes any Database over it. The application's concrete scope conforms to every use case's protocol; a test supplies a scope of mocks. The use case is written once and sees neither.

protocol CreatePostUseCaseScope {
    var postRepository: any PostRepository { get }
}

struct CreatePostUseCase<Scope: CreatePostUseCaseScope> {
    let database: any Database<Scope>

    func callAsFunction(input: CreatePostUseCaseInput) async throws {
        try await database.withTransaction { scope in
            try await scope.postRepository.create(title: input.title)
        }
    }
}

Drivers

| Package | Database | | --- | --- | | swift-persistence-postgres | PostgreSQL over PostgresNIO, with per-transaction session variables for row-level security |

A driver proves the commit and rollback contract in its own tests, against its own database.

Requirements

Swift 6.3, macOS 15 or Linux.

Development

swift test
swift-format lint --strict --recursive Sources Tests    # what the soundness check runs

Contributing

Pull requests are welcome. Keep a change focused, and prove new behaviour with a test.

License

MIT. See LICENSE.

Package Metadata

Repository: swift-microservices/swift-persistence

Default branch: main

README: README.md