Deserialize a JSON array to a list in C#

First, define a C# class that matches the structure of the JSON objects in the array.

For example, if the JSON contains information about books, you can create a Book class:

public class Book
{
    public string Title { get; set; }
    public string Author { get; set; }
    public int Year { get; set; }
    public double Price { get; set; }
}

When working with a JSON array, you can deserialize it into a list in a straightforward manner:

using System.Collections.Generic;
using System.Text.Json;

var bookList = JsonSerializer.Deserialize<List<Book>>(json);

This deserializes all the objects in the JSON array into a List<Book>, which you can then work with as usual.

Next, you will have a JSON array that you want to deserialize.

Valid JSON can be an object (i.e., {}) or an array (i.e., []).

Below is an example of a JSON array that contains 5 book objects:

[
    {"Title": "1984", "Author": "George Orwell", "Year": 1949, "Price": 9.99},
    {"Title": "To Kill a Mockingbird", "Author": "Harper Lee", "Year": 1960, "Price": 14.99},
    {"Title": "The Great Gatsby", "Author": "F. Scott Fitzgerald", "Year": 1925, "Price": 10.99},
    {"Title": "Moby Dick", "Author": "Herman Melville", "Year": 1851, "Price": 12.50},
    {"Title": "Pride and Prejudice", "Author": "Jane Austen", "Year": 1813, "Price": 8.99}
]

Now, you can use the JsonSerializer.Deserialize<T>() method to deserialize the JSON array into a List<Book>.

using System.Text.Json;

var list = JsonSerializer.Deserialize<List<Book>>(booksJson);

Console.WriteLine($"There are {list.Count} books.");

Output:

There are 5 books.

Deserialize and yield one object at a time

If you don’t want to load all the objects into memory at once, you can deserialize and yield one object at a time using DeserializeAsyncEnumerable().

using var bookJsonStream = new MemoryStream(Encoding.UTF8.GetBytes(booksJson));

await foreach (var book in JsonSerializer.DeserializeAsyncEnumerable<Book>(bookJsonStream))
{
    ProcessBook(book);
}

In this example, we are converting a string into a MemoryStream. It’s recommended to work with streams directly, such as reading from a file or an HTTP response stream.

Non-array collection of objects

Sometimes you will need to handle collections of objects stored in a JSON object instead of an array. Here’s an example:

{
  "1984": {
    "Author": "George Orwell",
    "Year": 1949,
    "Price": 9.99
  },
  "To Kill a Mockingbird": {
    "Author": "Harper Lee",
    "Year": 1960,
    "Price": 14.99
  },
  "The Great Gatsby": {
    "Author": "F. Scott Fitzgerald",
    "Year": 1925,
    "Price": 10.99
  }
}

This is a collection of key/value pairs (where the key is the book title and the value is the book object). You can deserialize it into a Dictionary<string, Book>:

var bookMap = JsonSerializer.Deserialize<Dictionary<string, Book>>(booksJson);

Keep things simple by deserializing into a class that matches the structure of the JSON.

If you're using Newtonsoft.Json instead of System.Text.Json, here's how you can deserialize the JSON array into a list:

using Newtonsoft.Json;

var books = JsonConvert.DeserializeObject<List<Book>>(booksJson);

Console.WriteLine($"Average price = ${books.Average(b => b.Price)}");

Output:

Average price = $11.09