Making data persist in Swift - swiftui

Question

I'm sorry if this is a naive question, but I need help getting this form to persist in core data. The variables are declared in the data model as strings. I simply cannot get this to cooperate with me. Also, the var wisconsin: String = "" is there because I can't call this view in my NavigationView without it throwing an error.
import SwiftUI
struct WisconsinToolOld: View {
//Variable
var wisconsin: String = ""
#Environment(\.managedObjectContext) private var viewContext
#State var saveInterval: Int = 5
var rateOptions = ["<12", ">12"]
#State var rate = ""
var body: some View {
List {
Section(header: Text("Spontaneous Respirations after 10 Minutes")) {
HStack {
Text("Respiratory Rate")
Spacer()
Picker("Rate", selection: $rate, content: {
ForEach(rateOptions, id: \.self, content: { rate in
Text(rate)
})
})
.pickerStyle(.segmented)
}
Section(header: Text("Result")) {
HStack {
Text("Raw Points")
Spacer()
Text("\(WisconsinToolInterpretation())")
}
}.navigationTitle("Wisconsin Tool")
}
}
func saveTool() {
do {
let wisconsin = Wisconsin(context: viewContext)
wisconsin.rate = rate
try viewContext.save()
} catch {
print(error.localizedDescription)
}
}
func WisconsinToolInterpretation() -> Int {
var points = 0
if rate == "<12" {
points += 3
}
else {
points += 1
}
return points
}
}