Swift JSON parse with colon in JSON key name - json

Question

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!

Answer 1

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)
}