如何比较Swift中的两个JSON对象？

Question

I have an json object and store it as initialData and after some changes in store the json object into another modifiedData. Now I am trying to compare two json object of initialData and modifiedData but i could not able to compare it.

Note: Here json object are dynamic value.

Sample code:

let jsonObjectVal = JSON(message.body)
let initialData = jsonObjectVal

In save action i have modifiedData object.

 let jsonObjectModVal = JSON(message.body)
 let modifiedData = jsonObjectModVal

 if initialFormDataJson == jsonObjectVal {
     print("json object are equal save handler")
   } else  {      
     print("json object are not equal save handler")
   }

Any help much appreciated pls...

Answer 1

Here's an example with a random data structure on how exactly you can do it:

import Foundation

final class YourObject: Decodable, Equatable {

    var field1: String
    var field2: Int
    var field3: [String : Double]

    static func == (lhs: YourObject, rhs: YourObject) -> Bool {
        lhs.field1 == rhs.field1
            && lhs.field2 == rhs.field2
            && lhs.field3 == rhs.field3
    }

}

let firstJSONString = """
{
   "field1":"Some string",
   "field2":1,
   "field3":{
      "Some string":2
   }
}
"""
let firstJSONData = firstJSONString.data(using: .utf8)!
let firstObject = try? JSONDecoder().decode(YourObject.self, from: firstJSONData)

let secondJSONString = """
{
   "field1":"Some string",
   "field2":1,
   "field3":{
      "Some string":2
   }
}
""" // Same.
let secondJSONData = secondJSONString.data(using: .utf8)!
let secondObject = try? JSONDecoder().decode(YourObject.self, from: secondJSONData)

let thirdJSONString = """
{
   "field1":"Some other string",
   "field2":2,
   "field3":{
      "Some string":3
   }
}
""" // Differs.
let thirdJSONData = thirdJSONString.data(using: .utf8)!
let thirdObject = try? JSONDecoder().decode(YourObject.self, from: thirdJSONData)

print(firstObject == secondObject) // true
print(firstObject == thirdObject) // false

Note: You mentioned that the object should be dynamic, that's why it's a class . If you needed a value object, you would be able to use struct and avoid manual implementation of the == operator.

It's just a start of course. Having a specific JSON structure in your hands you can always search for more complicated examples, internet swarms with them.

Answer 2

Create a NSObject class or struct from the JSON and compare all the properties to check for equality and return true/false accordingly. Equatable protocol will come in handy here.

class A: Equatable {
    func equalTo(rhs: A) -> Bool {
        // whatever equality means for two As
    }
}

func ==(lhs: A, rhs: A) -> Bool {
    return lhs.equalTo(rhs)
}

Answer 3

For Compare 2 objects use === operator

for eg.

let jsonObjectModVal = JSON(message.body)
 let modifiedData = jsonObjectModVal

 if initialFormDataJson === jsonObjectVal {
     print("json object are equal save handler")
   } else  {      
     print("json object are not equal save handler")
   }

Answer 4

If you want to compare two completely arbitrary JSON objects (eg for unit testing), I'd suggest using the GenericJSON library. Add it to your project and/or Package.swift, and then (borrowing from @lazarevzubov's answer):

import GenericJSON

// Assume `YourObject` is `Encodable`
let testObject = YourObject(field1: "Some string", field2: 1, field3: ["Some string": 2])

let expectedData = """
{
   "field1":"Some string",
   "field2":1,
   "field3":{
      "Some string":2
   }
}
""".data(using: .utf8)!

let expectedJSON = try? JSON(JSONSerialization.jsonObject(with: expectedData))
let actualJSON = try? JSON(encodable: testObject)

XCTAssertEqual(actualJSON, expectedJSON, "JSON should be equal")

A nice bonus is that you don't need to add any otherwise unnecessary Decodable or Equatable conformance to your model objects.