JuanGamez
May 1, 2024
202 views
0 votes
2 Answers

As a newcomer to .NET, I’m learning to work with JSON deserialization in C#. How can I efficiently deserialize a JSON array of objects with nested properties into a list of C# instances, while effectively handling the de-nesting process?

I have a JSON array representing a list of objects with nested properties, like this:

[
  {"name":"apple","properties":{"color":"red","flavor":"sweet"}},
  {"name":"orange","properties":{"color":"orange","flavor":"sour"}}
]

I want to deserialize this JSON into a list of C# objects. The C# class looks like this:

public class Fruit
{
    public string Name { get; set; }
    public string Color { get; set; }
    public string Flavor { get; set; }
}

It’s important to note that the structure of the C# object (Fruit) differs from the structure of the JSON object. In particular, the C# object does not have a "properties" variable.

Is there a more efficient way to achieve this than manually iterating through the JSON array elements and assigning values to Fruit objects?

My Code:

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

public class Fruit
{
    public string Name { get; set; }
    public string Color { get; set; }
    public string Flavor { get; set; }
}

class Program
{
    static void Main()
    {
        string json = "[{"name":"apple","properties":{"color":"red","flavor":"sweet"}},{"name":"orange","properties":{"color":"orange","flavor":"sour"}}]";

        // Deserialize into a list of Fruit objects
        List<Fruit> fruits = new List<Fruit>();

        var options = new JsonSerializerOptions
        {
            PropertyNameCaseInsensitive = true
        };

        var jsonObjects = JsonSerializer.Deserialize<List<JsonElement>>(json, options);
        
        foreach (var jsonObject in jsonObjects)
        {
            var fruit = new Fruit
            {
                Name = jsonObject.GetProperty("name").GetString(),
                Color = jsonObject.GetProperty("properties").GetProperty("color").GetString(),
                Flavor = jsonObject.GetProperty("properties").GetProperty("flavor").GetString()
            };

            fruits.Add(fruit);
        }

        // Print the fruits
        foreach (var fruit in fruits)
        {
            Console.WriteLine("Name: " + fruit.Name);
            Console.WriteLine("Color: " + fruit.Color);
            Console.WriteLine("Flavor: " + fruit.Flavor);
            Console.WriteLine();
        }
    }
}

Tags: asp.net-core c#deserialization json system.text.json

Answers

You have several ways of doing it. i think i would use a custom converter for this because:

It’s using Utf8JsonReader (more efficient in memory, especially in large files)
It’s cleaner, your logic is encapsulated in one place

public class FruitConverter : JsonConverter<Fruit>
{
    public override Fruit Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        Fruit fruit = new Fruit();

        while (reader.Read())
        {
            if (reader.TokenType == JsonTokenType.EndObject)
            {
                return fruit;
            }

            if (reader.TokenType == JsonTokenType.PropertyName)
            {
                string propertyName = reader.GetString();
                reader.Read();
                switch (propertyName)
                {
                    case "name":
                        fruit.Name = reader.GetString();
                        break;
                    case "properties":
                        while (reader.Read() && reader.TokenType != JsonTokenType.EndObject)
                        {
                            if (reader.TokenType == JsonTokenType.PropertyName)
                            {
                                string prop = reader.GetString();
                                reader.Read();
                                if (prop == "color")
                                    fruit.Color = reader.GetString();
                                else if (prop == "flavor")
                                    fruit.Flavor = reader.GetString();
                            }
                        }
                        break;
                }
            }
        }
        throw new Exception("json is not fotmatted well");
    }

    public override void Write(Utf8JsonWriter writer, Fruit value, JsonSerializerOptions options)
    {
        writer.WriteStartObject();
        writer.WriteString("name", value.Name);
        writer.WriteStartObject("properties");
        writer.WriteString("color", value.Color);
        writer.WriteString("flavor", value.Flavor);
        writer.WriteEndObject();
        writer.WriteEndObject();
    }
}

The shortest way (in one code line)

using System.Text.Json.Nodes;

List<Fruit> fruits = JsonNode.Parse(json)?.AsArray().Select(j => new Fruit { Name = (string)j["name"], Color = (string)j["properties"]["color"], Flavor = (string)j["properties"]["flavor"], })
                            .ToList();
// or 

using Newtonsoft.Json;
                            
List<Fruit> fruits = JArray.Parse(json)
                        .Select(j => new Fruit {Name= (string)j["name"], Color= (string)j["properties"]["color"],Flavor= (string)j["properties"]["flavor"], } )
                        .ToList();

or you can wrap this code in a converter

var fruits = JsonConvert.DeserializeObject<List<Fruit>>(json, new FruitConverter());

public class FruitConverter : JsonConverter<List<Fruit>>
{
    public override List<Fruit> ReadJson(JsonReader reader, Type objectType, List<Fruit> existingValue, bool hasExistingValue, JsonSerializer serializer)
    {
        var jArr = JArray.Load(reader);

        return jArr.Select(j => new Fruit { Name = (string)j["name"], Color = (string)j["properties"]["color"], Flavor = (string)j["properties"]["flavor"], })
                   .ToList();
    }
    public override bool CanWrite
    {
        get { return false; }
    }

    public override void WriteJson(JsonWriter writer, List<Fruit> value, JsonSerializer serializer)
    {
        throw new NotImplementedException();
    }
}

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Efficiently De-nesting Nested Properties in JSON Deserialization for C#

My Code:

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