如何在Firestore Swift中将特定字段的值分配给同一文档中的另一个字段？

let collectionRef = Firestore.firestore().collection("your_collection")
let documentRef = collectionRef.document("your_document")

documentRef.getDocument { (document, error) in
    if let document = document, document.exists {
        var data = document.data()!
        let field1Value = data["field1"] as! String
        data["field2"] = field1Value
        documentRef.updateData(data)
    } else {
        print("Document does not exist")
    }
}