As Realm doesn't support optionals, which are not Object subclasses, I'm trying to wrap a string into StringObject:
final class StringObject: Object {
dynamic var value: String = ""
convenience init?(_ value: String?) {
self.init()
if let value = value {
self.value = value
} else {
return nil
}
}
}
And use it like this:
final class Person: Object {
dynamic var firstName: String = ""
dynamic var lastName: StringObject? // can be optional
}
But this solution has a nasty side effect: as StringOptional values will be stored in their own table within the database, there will be countless duplicate values every time a StringObject is created. I tried making StringObject's value a primary key, but upon Person object's creation I receive an error:
Can't set primary key property 'lastName' to existing value 'Doe'
Which means that internally Realm does not upsert relationships.
Is there a better way to store optionals?
We actually released a beta of Realm that had support for optional strings and data properties, and it will hopefully be released more widely soon! In the meantime, you can try out the beta at https://github.com/realm/realm-cocoa/issues/628#issuecomment-106952727.
Related
I would like to make my class in Swift iterable.
My goal is to be able to create a class called Contact that holds properties such as the givenName, familyName, and middleName, like iOS CNContact. I would like to be able to have a class function that compares two instances of the class Contact, and finds which property the two contact objects have that match, so that say if both contacts have the same value for the givenName property, then the class function returns the result.
Here is a sample code:
class Contact {
static func compare(left: Contact, right: Contact) {
for property in left.properties {
if property == right.property {
// match is found
}
}
}
var givenName: String = ""
var familyName: String = ""
var middleName: String = ""
private var properties = [givenName, familyName, middleName]
}
let left = Contact()
let right = Contact()
Contact.compare(left: left, right: right)
I found posts that used mirroring and reflection, but I want to use Sequence and IteratorProtocol. I suspect there is already the ability to do exactly what I want to do. It seems to be a logical need that would arise.
What is the way to do this that has a balance between simplicity and the ability to address common needs to iterate through the instance properties of a class. An enumeration can be declared with given has values. Is there a way to make that work for this purpose? Is there a protocol that a class can use that assigns a hash value or other identifiable value that would allow for a sequential order to iterate through the properties of a class?
I was able to find posts and documentation that allowed me to get as far as the following code in playground that generated the following in debug window:
struct Name: Sequence {
typealias Iterator = NameIterator
typealias Element = Name
typealias Name = String
var name = "<name>"
func makeIterator() -> NameIterator {
return NameIterator()
}
}
struct NameIterator: IteratorProtocol {
typealias Iterator = String
typealias Element = Name
typealias Name = String
mutating func next() -> Name? {
let nextName = Name()
return nextName
}
}
let nameStrings = ["Debbie", "Harper", "Indivan", "Juniella"]
for nameString in nameStrings {
print(nameString)
}
Debbie
Harper
Indivan
Juniella
If you really don't want to use mirror, a straightforward way is to cycle through a list of key paths. This is particularly easy in your case because the properties are all strings:
class Contact {
static let properties = [\Contact.givenName, \Contact.familyName, \Contact.middleName]
static func compare(left: Contact, right: Contact) {
for property in properties {
if left[keyPath: property] == right[keyPath: property] {
print("got a match"); return
}
}
print("no match")
}
var givenName: String = ""
var familyName: String = ""
var middleName: String = ""
}
I think there's some confusion going on here.
The Sequence protocol and friends (IteratorProtocol, Collection, etc.) exist for you to be able to define custom sequences/collections that can leverage the existing collection algorithms (e.g. if you conform to Sequence, your type gets map "for free"). It has absolutely nothing to do with accessing object properties. If you want to do that, the only official reflection API in Swift is Mirror.
It's possible to...
...just Mirror, to create a standard collection (e.g. Array) of properties of an object
...just Sequence/Collection, to create a custom collection object that lists the property values of an object from hard-coded keypaths
...or you can use both, together, to create a custom collection object that uses Mirror to automatically list the properties of an object and their values
I am trying to follow the Model View ViewModel format for SwiftUI, but am running into an issue with UUID. I have an object of type TimeCode that has an attribute id of type UUID (TimeCode is created in xcdatamodels as a CoreData model). In order to create a TimeCodeViewModel object, I need to assign the id attribute in TimeCodeViewModel with the same UUID from the original TimeCode object. I therefore created this class definition to do so:
class TimeCodeViewModel: Identifiable {
var id: UUID
var fullName = ""
init(timeCode: TimeCode) {
self.id = timeCode.id
self.fullName = timeCode.fullName
}
// class methods
}
However, I get a compile time error saying that UUID is a get-only property. This makes sense, since you shouldn't be able to reassign the unique ID of an object to a different object, but in this case I am actually trying to describe the same object. Is it possible to assign self.id with the same UUID?
I guess another approach could be to make the UUID a string and then assign it to the view model, but is it then possible to convert the string back into a UUID? For example, I want to fetch the original TimeCode from CoreData using the UUID from the TimeCodeViewModel so I can save edits to other attributes of the TimeCode.
It would be interesting to see how the TimeCode Class looks like. I don't think that the id is set correctly. If you want a unique identifier as a String add the following to generate one:
var id: String = UUID().uuidString
You can share the string and therefore reference to the same object.
EDIT:
Regarding the new information, changing the class to the following might be an idea:
class TimeCodeViewModel: Identifiable {
var id: UUID {
return timeCode.id
}
var fullName = ""
private var timeCode: TimeCode
init(timeCode: TimeCode) {
self.timeCode = timeCode
self.fullName = timeCode.fullName
}
// class methods
}
As you can see the image, I totally mess up the Data Type (The red circle). Is there a way to change the Data Type into Integer?
EDIT
I want to change the data type from a String to an Int and I have existing data so I can't start with a fresh realm and just change the var type.
class Item: Object {
#objc dynamic var name: String?
#objc dynamic var itemid: String?
#objc dynamic var cateid: String?
}
I may have misunderstand the question but you appear to have existing data stored as as a String and you want to 'convert' all of those to an Int.
You cannot directly change the type to another type and have the stored data changed as well. If you do, it will be flagged with an error.
Error!
Migration is required due to the following errors:
- Property 'Item.itemid' has been changed from 'string' to 'int'.
You need to incorporate a migration block to 'convert' the string value to an Int. Assuming we add a new Int property to our object `item_id', something along these lines will migrate your strings to int's and in the case where the string is not a valid it, it will be assigned a value of 0
Realm.Configuration.defaultConfiguration = Realm.Configuration(
schemaVersion: 1,
migrationBlock: { migration, oldSchemaVersion in
if (oldSchemaVersion < 1) {
migration.enumerateObjects(ofType: Item.className()) { oldObject, newObject in
let stringValue = oldObject!["itemid"] as! String
newObject!["item_id"] = Int(stringValue) ?? 0
}
}
})
Also, as soon as Realm is accessed, the object models are written to the Realm file. So a simple matter of
let items = realm.object(Item.self)
Will store that model even if no data was ever written. If, after that line, the var type is changed from a String to an Int, it will throw the migration error.
Deleting the Realm and starting from scratch is one option if that's the case, and as mentioned above, a migration block.
If this is brand new model that has never been used, then as the comments and other answer suggest, just change the String to an Int.
Simply change the String to Int in your Object model. Please note that the Realm documentation says:
String, NSDate, and NSData properties can be declared as optional or non-optional using the standard Swift syntax.
So unlike the String in your previous model, you will not be able to declare your Int as optional. You have two options:
Declare a default value:
class Item: Object {
#objc dynamic var name: String?
#objc dynamic var itemid: Int = 0
#objc dynamic var cateid: Int = 0
}
Declare it as a RealmOptional:
class Item: Object {
#objc dynamic var name: String?
#objc dynamic var itemid = RealmOptional<Int>()
#objc dynamic var cateid = RealmOptional<Int>()
}
For more information on each solution please see this SO answer and the Realm documentation.
I am learning to parse JSON in Swift, coming from Android/Java, and I am using Unbox by John Sundell to help me with this, which reminds me of GSON.
Reference: Unbox pod
I use Realm as a database to store data locally.
Reference: Realm.io
It would be great to find a workflow to parse a class with JSON and save it to Realm. I don't want to have a struct that implements Unboxable AND a class that implements Object (Realm), because then I have to reflect the two. That isn't too much work for my current project, but it is kinda ugly...
Did any of you try a similar workflow?
I don't think you need two separate types. My suggestion is to create your objects as Swift classes that inherit from Realm's Object class, and then also conform them to the Unboxable protocol that Unbox offers. (Although the examples on Unbox's page use struct models, there's nothing in the code or documentation that indicates that classes wouldn't work.)
Realm model objects work just like any other classes: in addition to defining whatever properties on the objects you'd like stored in the database, you can also define methods and initializers, and even specify properties that you want Realm to ignore. This allows you to create an object that both serves as a Realm model and also a JSON model compatible with Unbox.
A more concise approach that doesn't require to override required initialisers (based on a tweet by Marin Todorov):
class Car: Object, Unboxable {
dynamic var vendor: String = ""
dynamic var modelName: String = ""
dynamic var electric: Bool = false
required convenience init(unboxer: Unboxer) throws {
self.init()
self.vendor = try unboxer.unbox(key: "vendor")
self.modelName = try unboxer.unbox(key: "modelName")
self.electric = try unboxer.unbox(key: "electric")
}
}
Here is an example that works perfectly for me:
class ProviderRealm: Object, Unboxable {
dynamic var identifier: String = "demo"
dynamic var name: String?
dynamic var logo: String?
/// Initializer used for unboxing of JSON string
required init(unboxer: Unboxer) throws {
self.identifier = (try? unboxer.unbox(key: "identifier")) ?? "demo"
self.name = try? unboxer.unbox(key: "name")
self.logo = try? unboxer.unbox(key: "logo")
super.init()
}
required init(realm: RLMRealm, schema: RLMObjectSchema) {
super.init(realm: realm, schema: schema)
}
required init() {
super.init()
}
required init(value: Any, schema: RLMSchema) {
super.init(value: value, schema: schema)
}
override static func primaryKey() -> String? {
return "identifier"
}
}
I was toying in the playground in xcode 7.3.1 with swift. I am a bit confused about the type casting in swift.
So, here is a bit of code that I tried.
class MediaItem {
var name: String
init(name: String) {
self.name = name
}
}
class Movie: MediaItem {
var director: String
init(name: String, director: String) {
self.director = director
super.init(name: name)
}
}
class Song: MediaItem {
var artist: String
init(name: String, artist: String) {
self.artist = artist
super.init(name: name)
}
}
var movieItem = Movie(name: "GOT", director: "RRMartin")
movieItem.dynamicType //Movie.Type
(movieItem as? MediaItem).dynamicType //Optional<MediaItem>.Type
var someItm = movieItem as! MediaItem //Movie
someItm.dynamicType //Movie.Type
I've shown the output from the playground in the comment. Here you can see the type in each line.
Now according the docs of apple, The conditional form, as?, returns an optional value of the type you are trying to downcast to. As per the docs, I am trying to downcast to MediaItem, and I am getting the MediaItem as optional type.
But when I use force unwrap(that is as!) the returned type is Movie. But I wanted it to be MediaItem.
Also, another thing to notice is that, the type is actually changed. Some data are actually truncated. Because when I tried to access the director property which is present in the Movie, I cannot access it. As I've downcast it.
So, if the type is downcast, why the returned type is Movie? Shouldn't it be MediaType?
So, my question is this, when I type cast some derived class(Movie) to base class(MediaType), shouldn't the converted type be base class(MediaType)?
dynamicType tells you what the underlying type of the object is. It doesn't tell you what the type of var currently referencing that object is.
For instance:
let a: Any = 3
a.dynamicType // Int.Type
Swift, of course, keeps track of these underlying types which is what allows you to later downcast a MediaItem to a Movie (if that is what it really is).
The confusion for you came when you did:
(movieItem as? MediaItem).dynamicType //Optional<MediaItem>.Type
An Optional is it's own type. It is an enumeration with two values: .None and .Some(T). The .Some value has an associated value that has its own dynamic type. In your example, when you asked for the dynamicType, it returned the underlying type of the Optional which is Optional<MediaItem>.Type. It didn't tell you what the dynamic type of the value associated with that Optional is.
Consider this:
let x = (movieItem as? MediaItem)
x.dynamicType // Optional<MediaItem>.Type
x!.dynamicType // Movie.Type