Defining swift extensions with generic functions for realm and object mapper

Question

I am working with Realm and ObjectMapper and would like to create some extensions to make my life easier when backing up some data to JSON. I have the following extensions defined:

extension Mappable where Self:Object {
    func getCompleteJSONDictionary() throws -> [String: Any]? {
        var returnValue: [String: Any]?

        if self.isManaged, let realm = self.realm, !realm.isInWriteTransaction {
            try realm.write {
                var data = self.toJSON()
                data["id"] = self.getPrimaryKeyValue()
                returnValue = data
            }
        } else {
            var data = self.toJSON()
            data["id"] = self.getPrimaryKeyValue()
            returnValue = data
        }

        return returnValue

    }
}

extension Results where Element:Object, Element:Mappable {

    func getAllCompleteJSONDictionaries() throws -> Array<[String:Any]>? {
        var array: Array<[String:Any]> = Array()
        for element in self {
            if let dictionary = try? element.getCompleteJSONDictionary(), let data = dictionary {
                 array.append(data)
            }
        }

        if array.count > 0 {
            return array
        } else {
            return nil
        }
    }
}

extension Realm {

func getJSONBackupData<T>(forTypes types: [T.Type]) throws -> [String: Any] where T:Object, T:Mappable {

    var data: [String: Any] = [:]

    try self.write {
        for type in types {
            let entities = self.objects(type)
            if let entityJsonData = try entities.getAllCompleteJSONDictionaries() {
                data[String(describing: type)] = entityJsonData
            }

        }
    }

    return data
}

}

The first two extensions work fine, but as soon as I try to use the last, the country class conforms to both Object and Mappable:

var finalData = realm.getJSONBackupData(forTypes:[Country.self])

I get an error that T cannot be inferred. I still get myself hopelessly muddled when it comes to generics in Swift so am guessing i am just not understanding the problem correctly. Is there an easy fix here or have I asked too much of the compiler?

Answer 1

The problem is that the Realm Objects does not conform to Mappable Protocol. So the Country Object is not Mappable and thus the complier is saying that Type Country.self cannot be inferred as Object and Mappable.