Swift3 CoreData with Extension

Question

I'm working on core data with extensions, and having errors below.

Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: 'executeFetchRequest:error: is not a valid NSFetchRequest.'

It's working well on host app still, however crashing on extensions with the same codes.

Debugger stopped when executed managedObjectContext.fetch(request)

func getDataString() -> String {

    var result = ""

    let entityDescription = NSEntityDescription.entity(forEntityName: "DataString", in: managedObjectContext)!
    let request : NSFetchRequest<NSFetchRequestResult> = DataString.fetchRequest()
    request.entity = entityDescription

    do {
        let results = try managedObjectContext.fetch(request)
        printDebug(message: "\tDataString Count : \(results.count)")

        if results.count > 0 {
            let row = results[0] as! NSManagedObject

            result = row.value(forKey: "data") as! String
        }
    } catch let error {
        printDebug(message: "ERROR : getDataString fetch")
        setErrorLog(errorText: "\(error)")
    }

    return result
}

This crashes even though written with try-catch. Please help.

Answer 1

Answer myself.

func getDataString() -> String {

var result = ""

let request = NSFetchRequest<NSFetchRequestResult>(entityName: "DataString")

do {
    let results = try managedObjectContext.fetch(request)
    printDebug(message: "\tDataString Count : \(results.count)")

    if results.count > 0 {
        let row = results[0] as! NSManagedObject

        result = row.value(forKey: "data") as! String
    }
} catch let error {
    printDebug(message: "ERROR : getDataString fetch")
    setErrorLog(errorText: "\(error)")
}

return result }

This worked.