How Can I Preserve Dictionary Keys When Serializing with Json.Net?

How to retain dictionary keys in Json.Net serialization

Json.Net is a commonly used serialization library, but when serializing objects containing dictionaries, you may encounter the problem of how to retain dictionary keys.

Let’s look at an example:

<code class="language-c#">public class Test
{
    public string X { get; set; }
    public Dictionary<string, string> Y { get; set; }
}</code>

Suppose you want to serialize this object into the following JSON format:

<code class="language-json">{
    "X" : "value",
    "key1": "value1",
    "key2": "value2"
}</code>

Here, the dictionary keys ("key1" and "key2") should be explicitly included in the JSON output.

Use the JsonExtensionData attribute to retain the dictionary

If using Json.Net 5.0.5 or higher, there is a simple solution. A dictionary can be promoted as part of the parent object's serialized representation by using the [JsonExtensionData] attribute. Just apply attributes to dictionary attributes:

<code class="language-c#">public class Test
{
    public string X { get; set; }

    [JsonExtensionData]
    public Dictionary<string, object> Y { get; set; }
}</code>

With this adjustment, the dictionary’s key-value pairs will be seamlessly integrated into the parent object’s JSON representation. Additionally, this mechanism works in both directions, allowing other JSON properties that do not map directly to class members to be deserialized into a dictionary.

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