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Use C# to get JSON Data from the Web and Map it to .NET Class => Made Easy!

, 12 Feb 2014
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Easy steps on how to get JSON formatted data from a web service, deserialize it, and map it to custom local class for further usage

Introduction 

This tip/trick demonstrates a complete and easy solution on how to get JSON formatted data from a web service, and map (deserialize) it to custom .NET class for further usage.

Sample Data

As an example, we will use https://openexchangerates.org service which provides latest currency rates formatted as JSON data. Here is a sample of how that data looks like:  

{
  "disclaimer": "This data is collected from various providers ...",
  "license": "Data collected from various providers with public-facing APIs ...",
  "timestamp": 1336741253,
  "base": "USD",
  "rates": {
    "AED": 3.6731,
    "AFN": 48.419998,
    "ALL": 107.949997,
    "AMD": 393.410004,
    "ANG": 1.79,
    "AOA": 94.949997,
    // ... more values ...
  }
} 

So, how do we retrieve them through C# on the server side and use them? Read on to find out.

How To - Three Easy Steps

Step 1. Install Json.Net library

Json.NET library provides an easy, and de-facto, standard way to convert (serialize) .NET class to JSON data, and JSON data back to .NET class (deserialize). 

The easiest way to install Json.Net library into your .NET project is via NuGet Package Manager Console by running this command:

install-package Newtonsoft.Json 

Alternatively, if you need to install it manually, download it from its project page on CodePlex.

Step 2. Create .NET class which will match JSON data format

If you are using Visual Studio 2012+, you're in luck, since you can just paste a sample JSON data and it will create a class for you, To do that, first create a new class .cs file, select it in project explorer, than copy sample JSON data to clipboard, go to EDIT > Paste Special > Paste JSON as classes (thanks to Dave Kerr for this tip). More information on this feature here

If that won't work for you, or you'd prefer to do it yourself, you'll need to define .NET class manually. It must exactly match the format of JSON data provided by openexchangerates.org:  

public class CurrencyRates {
  public string Disclaimer { get; set; }
  public string License { get; set; }
  public int TimeStamp { get; set; }
  public string Base { get; set; }
  public Dictionary<string, decimal> Rates { get; set; }
} 

Note that property names are not case sensitive, but the name has to exactly match the JSON one. Also, notice how "rates" JSON property is matched to a Dictionary<string, decimal>. If "rates" would have a singular value, they could alternatively be matched to an Array or IEnumerable.

Step 3. Create a method to retrieve JSON data and map it to .NET class

Now we will create the following universal method that can be re-used for any .NET class, where 'T' represents any .NET class that you need JSON data to be mapped to:

using System.Net;
using Newtonsoft.Json;

// ...

private static T _download_serialized_json_data<T>(string url) where T : new() {
  using (var w = new WebClient()) {
    var json_data = string.Empty;
    // attempt to download JSON data as a string
    try {
      json_data = w.DownloadString(url);
    }
    catch (Exception) {}
    // if string with JSON data is not empty, deserialize it to class and return its instance 
    return !string.IsNullOrEmpty(json_data) ? JsonConvert.DeserializeObject<T>(json_data) : new T();
  }
}

Here, at first, an instance of WebClient() System.Net class (a part of the .NET) downloads data from the specific URL as a plain string

Then, this string containing JSON data is mapped (deserialized) to any .NET class provided (CurrencyRates in our case). 

Deserialization is done via Json.NET library's method JsonConvert.DeserializeObject<T>(json_data), which attempts to match all JSON fields to the same .NET class fields. 

In this example, a call to a universal method _download_serialized_json_data<T>() can look like this:  

var url = "https://openexchangerates.org/api/latest.json?app_id=YOUR_APP_ID ";
var currencyRates = _download_serialized_json_data<CurrencyRates>(url); 

(Please note: if you want to use data provided by openexchangerates.org, first you need to get your unique App Id here: https://openexchangerates.org/signup/free^, than replace YOUR_APP_ID in the sample above.) 

Final Note 

And that's it! Now you can do anything you need with the data you've just retrieved. 

Good luck!

History

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

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About the Author

Mikhail-T
Web Developer
United States United States
MVC, .NET, AngularJS, JQuery, and POST/GET - all are my good friends!

Comments and Discussions

 
GeneralMy vote of 1 PinmemberDmitry Kirsanov19-Jun-14 5:09 
QuestionHow to access T and iterate [modified] Pinmembersuid00129-May-14 11:57 
AnswerRe: How to access T and iterate PinpremiumMikhail-T30-May-14 9:08 
GeneralRe: How to access T and iterate [modified] Pinmembersuid00130-May-14 16:42 
QuestionI got a JsonReaderException Pinmembernicocia10-Feb-14 4:06 
AnswerRe: I got a JsonReaderException PinmemberMikhail-T10-Feb-14 4:28 
GeneralRe: I got a JsonReaderException Pinmembernicocia10-Feb-14 4:38 
AnswerRe: I got a JsonReaderException PinmemberMikhail-T10-Feb-14 12:06 
GeneralRe: I got a JsonReaderException Pinmembernicocia10-Feb-14 21:23 
QuestionMessage Removed PinmemberAndrewGray123417-Jul-13 23:05 
AnswerRe: THIS DOES NOT WORK PinmemberMikhail Tsennykh18-Jul-13 7:02 
QuestionRe: Use C# to get JSON Data from the Web and Map it to .NET Class => Made Easy! PinmemberOmage femi17-May-13 6:46 
QuestionTwo minor questions [modified] PinmemberBillWoodruff30-Apr-13 1:26 
AnswerRe: Two minor questions PinmemberMikhail Tsennykh30-Apr-13 4:43 
Suggestion'Paste JSON As Classes' in Visual Studio PinmvpDave Kerr29-Apr-13 5:24 
GeneralRe: 'Paste JSON As Classes' in Visual Studio PinmemberBillWoodruff30-Apr-13 1:23 
GeneralRe: 'Paste JSON As Classes' in Visual Studio PinmvpDave Kerr30-Apr-13 2:17 
GeneralRe: 'Paste JSON As Classes' in Visual Studio PinmemberMikhail Tsennykh30-Apr-13 4:30 
GeneralRe: 'Paste JSON As Classes' in Visual Studio PinmvpDave Kerr30-Apr-13 4:37 
QuestionExample for POST JSON Pinmemberdeveloper24724-Jan-13 13:49 
QuestionMultilayered JSON results PinmemberJohn Mike H.19-Nov-12 9:03 
AnswerRe: Multilayered JSON results PinmemberMikhail Tsennykh19-Nov-12 11:27 
GeneralRe: Multilayered JSON results PinmemberJohn Mike H.20-Nov-12 3:58 
QuestionMixed JSon to Object Pinmemberrhythmdivine7-Oct-12 3:27 
AnswerRe: Mixed JSon to Object PinmemberMikhail Tsennykh7-Oct-12 7:05 

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