Strict data type for json file

Question

When I get the data from the json I first create a class and define all the variables I get in json for strict data type like my json file is

 {"fname":"Mark","lname":"jhony"}

so in angular i make the class like this

export class user{

 fname: string;
 lname : string;
}

I am confuse how to make the class for the following json data

{"fname":"Mark","lname":"jhony",
 "parcels":[
   {
    "parcelId":123,
    "parcelName :"asd",
    "parcelItems:[
       { 
        "itemId":2,
        "itemName":"perfume"
       },
       { 
         "itemId":4,
         "itemName":"soap"
       }
     ]
]}

I tried to add array in the class but not getting what would be the best way to handle it in angularjs.

score 3 · Accepted Answer · answered Oct 01 '18 at 13:13

3

Typically you would use an interface to represent a data structure of primitive values, for example:

interface ParcelItem {
  itemId: number;
  itemName: string;
}
interface Parcel {
  parcelId: number;
  parcelName: string;
  parcelItems: ParcelItem[];
}
interface User {
  fname: string;
  lname: string;
  Parcels: Parcel[];
}

Depending upon how you acquire the JSON and parse it you can specify the interface to use. The most simplistic example would be:

const user = JSON.parse(userJson) as User;

If you want to use a class perhaps for associated methods for data manipulation, you have to instantiate the class using a constructor. This might look like:

const userValues = JSON.parse(userJson);
const user = new User(userValues);

answered Oct 01 '18 at 13:13

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Important thing to note: this does not in any way *validate* the JSON. This means that later down the line you may get runtime error saying for example that the `lname` is undefined. The typing only verifies that the TypeScript code is consistent with it self at compile time. Nothing is known about runtime. As a TypeScript newb I had to have a colleague explain this to me until I understood that there is no *validation* in this pattern. He also mentioned that people specify their JSON using some other tools which then generate the TypeScript types. – Peter Lamberg Dec 15 '19 at 15:45
Here is a question with several answers on what to do if also *runtime* validation is needed: https://stackoverflow.com/questions/33800497/check-if-an-object-implements-an-interface-at-runtime-with-typescript And another question: https://stackoverflow.com/questions/14425568/interface-type-check-with-typescript – Peter Lamberg Dec 15 '19 at 15:55

score 0 · Answer 2 · answered Oct 01 '18 at 13:14

This would work.

export interface ParcelItemType {    
    itemId: number;
    itemName: string;
}

export interface ParcelType {
    parcelId: number;
    parcelName: string;
    parcelItems: ParcelItemType[];
}

export interface YourType {
   fname: string;
   lname: string;
   parcels: ParcelType[];
}

Strict data type for json file

2 Answers2