Get Values from JSON According to Condition - swift

Question

I have a local Json file in app bundle.
Existing Json file:
[
{
"id": 1001,
"key1": true,
"key2": "key2Value",
},
{
"id": 1002,
"key1": false,
"key2": "key2Value",
},
{
"id": 1003,
"key1": true,
"key2": "key2Value",
},
]
I want to loop over the json and get the ids if key1 value is true.
I tried like this but I got error:
let vehicleInfoTest: [Vehicle] = readJSONTest("vehicleInfo.json")
func readJSONTest<T: Codable>(_ named: String) -> T{
let data: Data
let ids: Int
do {
let fileURL = try FileManager.default
.url(for: .documentDirectory, in: .userDomainMask, appropriateFor: nil, create: false)
.appendingPathComponent("vehicleInfo.json")
data = try Data(contentsOf: fileURL)
// I can successfully get the foo
let foo = try JSONDecoder().decode(T.self, from: data)
// For loop gives an error: For-in loop requires 'Vehicle' to conform to 'Sequence'
for item in foo as! Vehicle{
if item.key1 == true{
ids = item.id
}
}
return foo
} catch {
fatalError("Couldn't find in main bundle.")
}
}
Finally ids should be like this:
ids = 1001, 1003
How can I get the ids?

Answer 1

Your code is a bit of a mess, you have a generic function that you try to use as a non-generic function and you have also some other messy stuff in it. Since you first need to call the generic function as step 1 and then do the filtering of the result in a second step the following code will give you the Id's where key1 is true
let vehicleInfoTest: [Vehicle] = readJSONTest("vehicleInfo.json")
let idValues = vehicleInfoTest.filter({ $0.key1 }).map( {$0.id })
Now to get this to work the function needs to be cleaned up
func readJSONTest<T: Codable>(_ named: String) -> T{
do {
let fileURL = try FileManager.default
.url(for: .documentDirectory, in: .userDomainMask, appropriateFor: nil, create: false)
.appendingPathComponent(named). //use parameter, not hardcoded string
let data = try Data(contentsOf: fileURL)
return try JSONDecoder().decode(T.self, from: data) // directly return decoded values
} catch {
fatalError("Decoding failed with error \(error)") // More useful error message
}
}

Answer 2

A simple
let ids = vehicles.filter { $0.key1 }.map { $0.id }
instead of your for loop should do the trick - however, this should not be part of the generic method.
Either readJSONTest is generic, or it knows about the internals of Vehicle, but it really shouldn't do both.
Also, please don't say x.key1 == true when key1 is already a non-optional Bool.

Answer 3

The non-generic code in the generic function makes no sense.
The loop presumes that T is an array and the type has a member key1. Filter the array outside the loop and make the function throw
func readJSONTest<T: Decodable>(_ named: String) throws -> T {
let fileURL = try FileManager.default
.url(for: .documentDirectory, in: .userDomainMask, appropriateFor: nil, create: false)
.appendingPathComponent("vehicleInfo.json")
let data = try Data(contentsOf: fileURL)
return try JSONDecoder().decode(T.self, from: data)
}
let vehicleInfoTest: [Vehicle] = try readJSONTest("vehicleInfo.json")
let ids = vehicleInfoTest.lazy.filter{$0.key1}.map{$0.id}