JSON Files

Introduction to JSON

JavaScript Object Notation (JSON) is a popular standard for representing structured data. It is similar to XML in that it stores data in a structured format, but it uses a different, more concise syntax. JSON files are often easier to read and write compared to XML, making them a popular choice for data interchange between applications.

Key Features of JSON

• Lightweight: JSON uses a minimal syntax, reducing the size of data representations.
• Human-Readable: While primarily designed for machine parsing, JSON is easier for humans to read than XML.
• Language-Independent: JSON is text-based and can be used with almost any programming language, including C#.

Working with JSON in C

To illustrate the use of JSON, we'll extend our book management system. Instead of storing a single book, we'll work with a list of books, which will be serialized and deserialized using JSON.

Using the List<T> Collection

We will use a List<Book> to store multiple books. The List<T> class is a dynamic data structure that can grow and shrink as items are added or removed. This makes it more flexible than arrays.

To use the List<T>, include the System.Collections.Generic namespace:

using System.Collections.Generic;

Initializing the List

First, we'll create a list and add several books to it:

List<Book> books = new List<Book>();
books.Add(new Book(1, "Wind in the Willows", "Kenneth Grahame", 14.99, 1908));
books.Add(new Book(2, "Alice in Wonderland", "Lewis Carroll", 9.99, 1895));
books.Add(new Book(3, "Treasure Island", "R.L. Stevenson", 14.99, 1883));
books.Add(new Book(4, "Oliver Twist", "Charles Dickens", 9.99, 1838));
books.Add(new Book(5, "Moby Dick", "Herman Melville", 2.99, 1851));
books.Add(new Book(6, "Frankenstein", "Mary Shelley", 4.99, 1818));

Serializing the List to JSON

We can save this list of books to a JSON file using the JsonSerializer class. Here's how to do it:

using System.Text.Json;  // Required for JsonSerializer
using System.IO;         // Required for StreamWriter

static void SaveAll(List<Book> books, string filename)
{
    using (StreamWriter writer = new StreamWriter(filename))
    {
        var options = new JsonSerializerOptions { WriteIndented = true };
        string json = JsonSerializer.Serialize(books, options);
        writer.Write(json);
    }
}

Explanation

1. Creating the StreamWriter: This creates a stream to write to the specified filename.
2. Setting Options: We use JsonSerializerOptions to format the JSON with indentation for better readability.
3. Serializing the List: JsonSerializer.Serialize converts the list of books to a JSON-formatted string.
4. Writing to File: The JSON string is written to the file using StreamWriter.Write().

Deserializing the JSON File

To read the data back from the JSON file, we use the following method:

using System.Text.Json;  // Required for JsonSerializer
using System.IO;         // Required for StreamReader

static List<Book> Load(string filename)
{
    using (StreamReader reader = new StreamReader(filename))
    {
        string json = reader.ReadToEnd();
        return JsonSerializer.Deserialize<List<Book>>(json);
    }
}

Explanation

1. Reading the File: StreamReader reads the entire contents of the JSON file into a string.
2. Deserializing: JsonSerializer.Deserialize converts the JSON string back into a List<Book>.

Defining the Book Struct

To work with the JsonSerializer, our Book struct must use properties instead of fields:

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

    public Book(int id, string title, string author, double price, int year)
    {
        Id = id;
        Title = title;
        Author = author;
        Price = price;
        Year = year;
    }
}

Properties vs. Fields

• Fields: Simple variables inside a class or struct, e.g., public string firstName;.
• Properties: Encapsulate fields with getter and setter methods, e.g., public int Age { get; set; }.

For serialization to work correctly, the Book struct must expose its data through properties.

Comparing JSON and XML Serialization

• JSON:

  • More compact and readable.
  • Easier to parse in many programming languages.
  • Widely used for web APIs.

• XML:

  • More verbose but supports more complex data structures.
  • Offers features like schemas and namespaces.
  • Still used in many enterprise systems.

Exercises

1. Modify the Book struct to include a list of Review objects, and update the serialization code to handle this nested structure.
2. Write a method to update the price of a book in the JSON file and re-serialize it.
3. Research the difference between JSON and YAML. Which would you prefer for a configuration file and why?

Further Reading

• JSON in C#
• Comparison between JSON and XML

Understanding serialization with JSON will enable you to efficiently store and exchange data between applications.