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Call a Function - Swift SDK

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  • Call a Function by Name
  • Async/Await Call a Function


Make sure to sanitize client data to protect against code injection when using Functions.

Consider an Atlas App Services Function named concatenate that takes two arguments, concatenates them, and returns the result:

// concatenate: concatenate two strings
exports = function(a, b) {
return a + b;

To execute a function from the Swift SDK, use the functions object on the currently logged-in user.

The functions object has dynamic members corresponding to functions. In this case, functions.concatenate() refers to the concatenate function. Pass a BSONArray of arguments. The trailing closure is the completion handler to call when the function call is complete. This handler is executed on a non-main global DispatchQueue.

New in version 10.16.0.

The Realm Swift SDK offers async/await versions of the User.function methods.

func testAsyncCallFunction() async {
let app = App(id: YOUR_APP_SERVICES_APP_ID)
// ... log in ...
let user = app.currentUser!
do {
// The dynamic member name `concatenate` is directly associated with the
// function name. The first argument is the `BSONArray` of arguments to be
// provided to the function - in this case, a string that represents a
// username and a string that represents an email domain.
let concatenatedString = try await user.functions.concatenate([AnyBSON("john.smith"), AnyBSON("")])
print("Called function 'concatenate' and got result: \(concatenatedString)")
assert(concatenatedString == "")
} catch {
print("Function call failed: \(error.localizedDescription)")

Starting with Realm Swift SDK Versions 10.15.0 and 10.16.0, many of the Realm APIs support the Swift async/await syntax. Projects must meet these requirements:

Swift SDK Version
Swift Version Requirement
Supported OS
Swift 5.6
iOS 13.x
10.15.0 or 10.16.0
Swift 5.5
iOS 15.x

If your app accesses Realm in an async/await context, mark the code with @MainActor to avoid threading-related crashes.

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