How to use JsonDocument to read JSON in C#

Consider the following JSON object representing a book:

{
  "title": "The Great Gatsby",
  "author": "F. Scott Fitzgerald",
  "year": 1925,
  "genres": ["Fiction", "Classic", "Literature"]
}

If you're only interested in the book's title, you can use JsonDocument to read the JSON string and extract the title value without deserializing the entire structure:

using System.Text.Json;

string json = /* your JSON string here */;

using (var jsonDoc = JsonDocument.Parse(json))
{
    JsonElement title = jsonDoc.RootElement.GetProperty("title");
    Console.WriteLine($"Book title = {title.GetString()}");
}

Output:

Book title = The Great Gatsby

How to use JsonDocument in C#?

Check if a Property Exists

When using JsonElement.GetProperty(), a KeyNotFoundException is thrown if the property doesn't exist. To check for a property without throwing an exception, use TryGetProperty():

using (var jsonDoc = JsonDocument.Parse(json))
{
    if (jsonDoc.RootElement.TryGetProperty("year", out JsonElement year))
    {
        Console.WriteLine($"Year property exists and has int value = {year.GetInt32()}");
    }
}

Output:

Year property exists and has int value = 1925

Loop Through a JSON Object’s Properties

To loop through a JSON object's properties, use EnumerateObject().

For example, let's loop through the properties of the book JSON:

using (var jsonDoc = JsonDocument.Parse(json))
{
    foreach (var property in jsonDoc.RootElement.EnumerateObject())
    {
        Console.WriteLine($"{property.Name} ValueKind={property.Value.ValueKind} Value={property.Value}");
    }
}

Output:

title ValueKind=String Value=The Great Gatsby
author ValueKind=String Value=F. Scott Fitzgerald
year ValueKind=Number Value=1925
genres ValueKind=Array Value=[]

Loop Through a JSON Array

To loop through the values in a JSON array, use EnumerateArray().

For example, if you want to loop through and print the genres of the book:

using (var jsonDoc = JsonDocument.Parse(json))
{
    JsonElement genres = jsonDoc.RootElement.GetProperty("genres");
    foreach (var genre in genres.EnumerateArray())
    {
        Console.WriteLine($"Genre: {genre.GetString()}");
    }
}

Output:

Genre: Fiction
Genre: Classic
Genre: Literature

Deserialize a Nested Object

You can also extract a nested object using GetProperty() and then deserialize it into a specific type.

Consider a more complex JSON structure where you want to extract and deserialize information about the author:

{
  "title": "The Great Gatsby",
  "author": {
      "name": "F. Scott Fitzgerald",
      "birthYear": 1896
  },
  "year": 1925
}

Using JsonDocument, you can extract the author details like this:

using (var jsonDoc = JsonDocument.Parse(json))
{
    var authorElement = jsonDoc.RootElement.GetProperty("author");
    var author = authorElement.Deserialize<Author>(jsonOptions);
    Console.WriteLine($"Author: {author.Name}, Birth Year: {author.BirthYear}");
}

This would return an Author object with the appropriate values.

This revised example illustrates how to utilize JsonDocument to read JSON data effectively in C#, using a book-related JSON structure.