How to Deserialize Nested JSON to a Nested Dictionary of Objects with Proper C# Types Using System.Text.Json?

Deserializing Nested JSON to Nested Dictionary of Object with Proper C# Types

In C# .Net Core 3.1 using System.Text.Json, deserializing nested JSON objects to Dictionary may result in every object being a JsonElement. However, we can customize the deserialization process to obtain proper C# types for each JSON property type:

Custom JsonConverter: ObjectAsPrimitiveConverter

As System.Text.Json lacks built-in support for deserializing free-form JSON into primitive types, we need a custom JsonConverter, ObjectAsPrimitiveConverter, which provides the following functionality:

• Convert String: JSON string properties to C# string
• Convert Number: JSON number properties to C# int/double
• Convert Object: JSON object properties to Dictionary

Code Implementation:

public class ObjectAsPrimitiveConverter : JsonConverter<object>
{
    // Configure converter settings (float format, unknown number handling, object format)
    ...

    public override void Write(Utf8JsonWriter writer, object value, JsonSerializerOptions options)
    {
        // Handle custom serialization if needed
    }

    public override object Read(ref Utf8JsonReader reader, Type typeToConvert, JsonSerializerOptions options)
    {
        // Handle custom deserialization based on token type
    }
}

Configuration and Usage:

To use the custom converter, configure your JsonSerializerOptions with the ObjectAsPrimitiveConverter and specify the desired settings:

var options = new JsonSerializerOptions
{
    Converters = { new ObjectAsPrimitiveConverter() },
    WriteIndented = true,
};

// Deserialize to object or dynamic
dynamic d = JsonSerializer.Deserialize<dynamic>(json, options);

Notes:

• The converter handles edge cases such as numbers with arbitrary precision, which may not fit into primitive C# types. It provides options for error handling or returning a JsonElement for such numbers.
• You can configure the converter to use different float formats (double/decimal) and object representations (Dictionary or ExpandoObject).
• A demo fiddle is available for reference.

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