How to validate values before creating Realm object (in RealmSwift) - ios

Question

My application code gets JSON data from a server, converts it to a Dictionary and then uses that to hydrate and attempt to save a RealmSwift object with a matching schema.
I ran into a crash caused by a Float value coming into a field that was declared as Int in the model. RLMException was thrown.
As suggested in this thread, one doesn't simply try to catch RLMException.
My question is, is that answer correct? And, if so, what is the correct way to prevent a crash when an unexpected value is found? Isn't there some sort of validation mechanism that I can run on all of the values before attempting to set them?

Answer 1

You can use third party frameworks for mapping JSON to Realm objects, like ObjectMapper and use it's failable initializer to validate your JSON.
This failable initializer can be used for JSON validation prior to object serialization. Returning nil within the function will prevent the mapping from occuring. You can inspect the JSON stored within the Map object to do your validation.

Answer 2

You can use this to see if everything is ok with json parameters
static func createFromJSONDictionary(json: JSONDictionary) throws -> MyObject {
guard let
property1 = json["property1"] as? Int,
property2 = json["property1"] as? String else {
// Throw error.... or create with default values
throw NSError(domain: "", code: 0, userInfo: nil)
}
// Everything is fine, create object and return it
let object = MyObject()
object.something = property1
return object
}

Answer 3

I ended up writing an extension to handle this. At the moment I'm only validating numbers and dates, but the switch statement could check every single property type easily.
extension Object {
public convenience init( withDictionary rawData: [String:AnyObject] ) {
var sanitizedData = rawData
let dynamicSelf = self.dynamicType
let schema = dynamicSelf.sharedSchema()
for property in schema.properties {
guard let value = sanitizedData[property.name] else { continue }
var isValid = true
switch property.type {
case .Double:
let val = Double(String(value))
if val == nil || val!.isNaN {
isValid = false
}
case .Float:
let val = Float(String(value))
if val == nil || val!.isNaN {
isValid = false
}
case .Int:
if Int(String(value)) == nil {
isValid = false
}
case .Date:
if Int64(String(value)) == nil {
isValid = false
} else {
sanitizedData[property.name] = NSDate(timeIntervalSince1970: value.doubleValue / 1000)
}
default:
break
}
if !isValid {
log.error( "Found invalid value: \(value) for property \(property.name) of \(dynamicSelf)" )
sanitizedData.removeValueForKey(property.name)
}
}
self.init( value: sanitizedData )
}
}