I have a json in following format:
let json = """
{
"stuff": {
"1": "one",
"2": "two",
"4": "four"
}
}
question is how can i make my
struct Stuff: Codable, Equatable {
let 1: String
let 2: String
let 4: String
}
compile and work?
i use to call this with below, and it works fine for everything but if let name starts with number it obviously won't compile
let obj = try? JSONDecoder().decode(T.self, from: data)
You can't. A variable must not start with a numeric character. Unalterable rule.
But you can map the names with CodingKeys
struct Stuff: Codable, Equatable {
let one, two, four: String
private enum CodingKeys : String, CodingKey { case one = "1", two = "2", four = "4"}
}
You can't. RFC 7159 standard for JSON dictates that the object key must be a string.
object = begin-object [ member *( value-separator member ) ]
end-object
member = string name-separator value
Related
When I make an API request, I get returned a JSON structure that contains several objects which all have unique key value names. Therefore I cannot use the regular Decodable protocol to break down the JSON into different instances. However, these key value names are found elsewhere in my JSON structure under known constant values that I can access normally. Here is some example code I created to demonstrate my issue:
let jsonString = """
{
"uniqueObjects": {
"uniqueObject:1132435": {
"firstName": "John"
"lastName": "Smith"
}
"uniqueObject2:119672": {
"firstName": "Jane"
"lastName": "Doe"
}
"uniqueObject3:008997": {
"firstName": "Sam"
"lastName": "Greenfield"
}
}
"keys": {
"object1": {
"key": "uniqueObject1:132435"
}
"object2": {
"key": "uniqueObject2:119672"
}
"object3": {
"key": "uniqueObject3:008997"
}
}
"""
let jsonData = Data(jsonString.utf8)
let decodedData = try? JSONDecoder().decode(JSONData.self, from: jsonData)
print(decodedData?.uniqueObjects.firstObject.firstName ?? "No data decoded")
struct JSONData: Decodable {
let uniqueObjects: Object
let keys: KeyObjects
}
struct Object: Decodable {
let firstObject: Names
let secondObject: Names
let thirdObject: Names
private enum DynamicCodingKeys: String, CodingKey {
case firstObject = "???" // this needs to be mapped to the unique value for object 1
case secondObject = "??" // this needs to be mapped to the unique value for object 2
case thirdObject = "????" // etc.
// I don't think this works because Xcode says that the strings must be raw literals
}
}
struct KeyObjects: Decodable {
let object1: Key
let object2: Key
let object3: Key
}
struct Key: Decodable {
let key: String
}
struct Names: Decodable {
let firstName: String
let lastName: String
}
The approach I took here, which is definitely wrong, was to create a coding key for each of the unique objects and map its name to a String that would be somehow be decoded from its relative key value pair in the key object. CodingKeys, at least what I have tried, do not allow you to do this so I need a new method in order to access this code. I also need to know how I can reference the data once I decode it (just printing it out for now). Help and a short explanation would be much appreciated as I am a beginner developer. Thanks!
Unless I have misunderstood it looks to me like you are over complicating things. This is how I would define the types for decoding the json
struct Response: Codable {
let uniqueObjects: [String: User]
let keys: [String: ObjectKey]
}
struct ObjectKey: Codable {
let key: String
}
struct User: Codable {
let firstName: String
let lastName: String
}
Can you use Swift's JSONDecoder on JSON that has a colon in the key name? Colons are reserved in Swift for things like indicating Type and Protocol, so when I try to create a struct with a matching keyname to use with JSONDecoder.decode, I'll get an error. Example API:
https://api.teleport.org/api/urban_areas/
the list of cities I'd like to access is in the key:
"ua:item"
But Swift doesn't allow a property with this name for easy JSONDecoding.
I'd like to stick with JSONDecoder since it's so easy & elegant. Is there an easy workaround for this, or do I need to fall back on older parsing techniques. Thanks!
Here is a reduced version of the JSON response for the API that you are calling. I have just limited the number of items in each array as it becomes to repetitive to just list similar items over and over again.
let data = """
{
"_links": {
"curies": [
{
"href": "https://developers.teleport.org/api/resources/Location/#!/relations/{rel}/",
"name": "location",
"templated": true
}
],
"self": {
"href": "https://api.teleport.org/api/urban_areas/"
},
"ua:item": [
{
"href": "https://api.teleport.org/api/urban_areas/slug:aarhus/",
"name": "Aarhus"
},
{
"href": "https://api.teleport.org/api/urban_areas/slug:adelaide/",
"name": "Adelaide"
}
]
},
"count": 266
}
""".data(using: .utf8)!
There are are couple of gotchas in the JSON, but we can fix them easily by using CodingKeys. Notice the case value of the CodingKey must match the variable name, the string value of the coding key must match the value in the JSON, where the values are the same we can skip writing the string value.
There are three issues with the JSON
_links
self
ua:item
By convention variables in Swift do not usually start with an underscore, so it makes sense to remove that. We can do that with the first set of CodingKeys.
self is a reserved word in Swift so we should replace that with something more appropriate, in this case I chose link.
As you have already noticed you cannot have colons in the name of variables. We can replace this with something more suitable, in this case uaItem.
This gives the following struct. Which if you take with the above data variable and past into a playground it should all decode nicely.
struct Response: Decodable {
let links: Links
let count: Int
// These are the coding keys for Response
enum CodingKeys: String, CodingKey {
case links = "_links"
case count
}
struct Links: Decodable {
let curies: [Curie]
let link: HREF
let uaItem: [UAItem]
// These are the coding keys for Links
enum CodingKeys: String, CodingKey {
case curies
case link = "self"
case uaItem = "ua:item"
}
}
struct Curie: Decodable {
let href: String
let name: String
let templated: Bool
}
struct HREF: Decodable {
let href: String
}
struct UAItem: Decodable {
let href: String
let name: String
}
}
do {
let result = try JSONDecoder().decode(Response.self, from: data)
print(result)
} catch {
print(error)
}
I download a JSON file from my database which returns the following string:
["ingredients": asdasdasd,
"price": 14,
"_id":
{
"$oid" = 5e8e3706f00ca80f251485c3;
},
"category": sadad,
"available": Disponibile,
"name": asdadasd]
I then convert this string to data to then convert it to a Dictionary<String, Any>
if let myData = responseString.data(using: .utf8) {
do {
let myArray = try (JSONSerialization.jsonObject(with: myData) as? [Dictionary<String, Any>])!
completion(myArray, nil)
} catch let error as NSError {
print("error:" + String(describing: error))
completion(nil, error)
}
}
This works perfectly fine, as I can get, let's say, the price parameter doing myArray["price"].
The problem arises when I try to get the Id parameter, as when I do myArray["_id"] I get:
{
"$oid" = 5e8e370af00ca80f251485cf;
}
I would like to directly get the ID parameter, and I can't parse this value to JSON as it is not in JSON format. At the moment I am fixing the issue by manipulating this string replacing the = with :, removing the ; and other nasty stuff, but I am sure there is a more efficient way to solve the issue.
myArray["_id"] is a Dictionary in your myArray.So you have to convert your myArray["_id"] to dictionary and then you can access the id.
try this
let id = (myArray["_id"] as Dictionary ?? [:])["$oid"] as? String ?? ""
What you've posted looks like debugger print output, not JSON from your server. I'm going to assume that your JSON actually looks like this:
[
{
"ingredients": "asdasdasd",
"price": 14,
"_id": {
"$oid": "5e8e3706f00ca80f251485c3"
},
"category": "sadad",
"available": "Disponibile",
"name": "asdadasd"
}
]
Given that, you could use a model struct like
struct Recipe: Codable {
let ingredients: String
let price: Int
let id: ID
let category, available, name: String
enum CodingKeys: String, CodingKey {
case ingredients, price
case id = "_id"
case category, available, name
}
}
struct ID: Codable {
let oid: String
enum CodingKeys: String, CodingKey {
case oid = "$oid"
}
}
typealias Recipes = [Recipe]
to parse it using
do {
let recipes = try JSONDecoder(Recipes.self, from: myData)
let firstOid = recipe.first?.id.oid
} catch {
print(error)
}
That said, I would recommend avoiding generic names like myArray for your variables.
Also, when retrieving JSON data from your server, it's not necessary to first convert them to a String and then back to Data before passing it to the JSON parser - simply pass the raw server data along.
I'm creating a SwiftUI flashcard app, and I have no problem using Codable and following the technique Apple demonstrated with their landmarks tutorial app for importing JSON data in order to create their array of objects.
However, two of my flashcard objects' properties don't need to be loaded from JSON, and I could minimize the text needed in the JSON file if I could initialize those values separately instead of loading them from JSON. The problem is I cannot get JSON data to load without an error unless it maps exactly to ALL the object's properties, even if the missing properties are hardcoded with values.
Here is my object model:
import SwiftUI
class Flashcard: Codable, Identifiable {
let id: Int
var status: Int
let chapter: Int
let question: String
let answer: String
let reference: String
}
Here is JSON that works:
[
{
"id": 1,
"status": 0,
"chapter": 1,
"question": "This is the question",
"answer": "This is the answer",
"reference": "This is the reference"
}
//other card info repeated after with a comma separating each
]
Instead of having "id" and "status" listed unecessarily in the JSON, I would prefer to change the model to something like this:
import SwiftUI
class Flashcard: Codable, Identifiable {
let id = UUID()
var status: Int = 0
//only load these from JSON:
let chapter: Int
let question: String
let answer: String
let reference: String
}
...and then I theoretically should be able to eliminate "id" and "status" from the JSON (but I can't). Is there a simple way to do this that prevents the error from JSON not mapping completely to the object?
Yes, you can do this by setting the coding keys on your Codable class. Just leave out the ones that you don't want to update from the json.
class Flashcard: Codable, Identifiable {
let id = UUID()
var status: Int = 0
let chapter: Int
let question: String
let answer: String
let reference: String
enum CodingKeys: String, CodingKey {
case chapter, question, answer, reference
}
}
There is a great article by HackingWithSwift on Codable here
you can use CodingKeys to define what fields to extract from the JSON.
class Flashcard: Codable, Identifiable {
enum CodingKeys: CodingKey {
case chapter
case question
case answer
case reference
}
let id = UUID()
var status: Int = 0
//only load these from JSON:
let chapter: Int
let question: String
let answer: String
let reference: String
}
The docuemntation has a good explanation (for once) of this under `Encoding and Decoding Custom Types`
I have a JSON file:
{
"name": "Jens",
"time": "11.45",
"date": "2018:04:17",
"differentTimestamps":[""]
"aWholeLotOfnames":{
"name1": "Karl"
"name2": "pär"
}
How to parse above JSON ? I have checked this tutorial https://www.youtube.com/watch?v=YY3bTxgxWss. One text tutorial to but i don't get how to make a variable that can take a
"nameOfVar"{}
If it's not a dictionary. The tutorial are using a var nameOfVar: [what should be here in this case] for one that nearly looks like it. The thing is though that theirs are starting with a [{ and ends with a }] while mine only starts with a {? i don't know how to solve this?
Creating corresponding Swift data types for JSON is very easy.
A dictionary {} can be decoded into a class / struct where the keys become properties / members.
An array [] can be decoded into an array of the given (decodable) type.
Any value in double quotes is String even "12" or "false".
Numeric floating point values are Double, integer values are Int and true / false is Bool
null is nil
let jsonString = """
{
"name": "Jens",
"time": "11.45",
"date": "2018:04:17",
"differentTimestamps":[""],
"aWholeLotOfnames":{
"name1": "Karl",
"name2": "pär"
}
}
"""
struct Item: Decodable {
let name, time, date: String
let differentTimestamps: [String]
let aWholeLotOfnames: AWholeLotOfnames
}
struct AWholeLotOfnames : Decodable {
let name1, name2 : String
}
let data = Data(jsonString.utf8)
do {
let result = try JSONDecoder().decode(Item.self, from: data)
print(result)
} catch { print(error) }