Theo, the Neo4j Swift driver, works well with Vapor 4.
For future reference: This post was written with Theo 5.2.0, Vapor 4.15.2 and Swift 5.2.4

Let's have a look at how to use it together, starting with the crudest example:

	import Vapor
	import Theo
	func theoClient(completion: @escaping (BoltClient) -> ()) {
	do {
	let client = try BoltClient(hostname: "127.0.0.1",
	port: 7687,
	username: "neo4j",
	password: "test",
	encrypted: true)
	client.connect { result in
	let isSuccess = try! result.get()
	assert(isSuccess)
	completion(client)
	}
	} catch {
	print("Error! \(String(describing: error))")
	}
	}
	func routes(_ app: Application) throws {
	app.get { req -> EventLoopFuture<String> in
	let promise: EventLoopPromise<String> = req.eventLoop.makePromise()
	theoClient() { theo in
	let newNode = Node(label: "New", properties: [ "createdTime": Date().timeIntervalSince1970 ])
	theo.createAndReturnNode(node: newNode) { result in
	do {
	let node = try result.get()
	assert(node.labels.first! == "New")
	promise.completeWith(.success("Newly created node!"))
	} catch {
	promise.completeWith(.failure(error))
	}
	}
	}
	return promise.futureResult
	}
	}

view raw vapor-with-theo-getting-started.swift hosted with ❤ by GitHub

In the code above, we start with the theoClient function that in it's completion block provides a Bolt client. Bolt is the binary protocol used to talk to a Neo4j instance. I've configured it to connect to the instance on my machine at port 7687, the default Bolt port. I provide a username and password, and ask it to connect via SSL, a configuration you may know from the Neo4j browser as bolt+s.

For this example, I've written a router with only one endpoint and implemented it straight away. When a request is made, we make a promise to Vapor that we'll return a string. Then we ask for a Theo client, and define a new node we want to insert. The node contains a single label: "New", and a single property "createdTime", with the current time as a TimeInterval (a.k.a. Double).

We ask the client to create it, and if it is successful, we fulfil our promise saying "Newly created node!". If, however, there is a problem, we complete with a failure and report the error.