How to map custom Enum/RawRepresentable to dictionary with ObjectMapper? - ios

Question

using the following simplified structure:
class Property: Mappable {
var path: String?
override func mapping(map: Map) {
path <- map["path"]
}
}
class Specification {
enum Name: String {
case Small = "SMALL"
case Medium = "MEDIUM"
}
}
class ItemWithImages: Mappable {
var properties: [Specification.Name : Property]?
override func mapping(map: Map) {
properties <- (map["properties"], EnumTransform<Specification.Name>())
}
}
... with that JSON:
[{"properties: ["SMALL": {"path": "http://..."}, "MEDIUM": {"path": "http://..."}]}]
... produces when using EnumTransform() as Transform the following (reasonable) compile error:
Binary operator '<-' cannot be applied to operands of type '[Specification.Name : Property]?' and '(Map, EnumTransform<Specification.Name>)'
So how does a custom TransformType have to look like, to map that dictionary the right way?
You can find the source of EnumTransform here: https://github.com/Hearst-DD/ObjectMapper/blob/master/ObjectMapper/Transforms/EnumTransform.swift
Thanks!

Answer 1

TransformTypes are IMHO primary designed to transform values and not keys. And your example is a little bit complicated because even value is not just basic type.
What do you think about this little hack?
struct ItemWithImages: Mappable {
var properties: [Specification.Name : Property]?
init?(_ map: Map) {
}
mutating func mapping(map: Map) {
let stringProperties: [String: Property]?
// map local variable
stringProperties <- map["properties"]
// post process local variable
if let stringProperties = stringProperties {
properties = [:]
for (key, value) in stringProperties {
if let name = Specification.Name(rawValue: key) {
properties?[name] = value
}
}
}
}
}

Answer 2

We should use DictionaryTransform instead of EnumTransform. We are transforming type of Dictionary [String:Any] to [Key:Value]. In our case type is [Specification.Name: Property].
Key need to conforms protocols like Hashable, RawRepresentable, and Key.RawValue should be String.
And Value Should be conforms Mappable Protocol.
class Property: Mappable {
var path: String?
override func mapping(map: Map) {
path <- map["path"]
}
}
class Specification {
enum Name: String {
case Small = "SMALL"
case Medium = "MEDIUM"
}
}
class ItemWithImages: Mappable {
var properties: [Specification.Name : Property]?
override func mapping(map: Map) {
properties <- (map["properties"], DictionaryTransform<Specification.Name,Property>())
}
}