How do I customize property names when serializing JSON with Newtonsoft.Json

1. Using the `[JsonProperty]` Attribute

You can directly modify the property names by decorating the properties with the `[JsonProperty]` attribute. This allows you to specify a custom name for each property during serialization and deserialization.

csharp
public class Person
{
    [JsonProperty("first_name")]
    public string FirstName { get; set; }

    [JsonProperty("last_name")]
    public string LastName { get; set; }

    public int Age { get; set; }
}

In this example, `FirstName` will be serialized as `"first_name"`, and `LastName` as `"last_name"`. The `Age` property will retain its original name.

2. Implementing a Custom Naming Strategy

Newtonsoft.Json supports various naming strategies, such as `CamelCaseNamingStrategy`. You can apply these strategies globally or to specific classes/properties using the `[JsonProperty]` attribute or by configuring a `DefaultContractResolver`.

To apply a naming strategy globally, you can configure the `DefaultContractResolver`:

csharp
var contractResolver = new DefaultContractResolver
{
    NamingStrategy = new CamelCaseNamingStrategy()
};

var jsonSerializerSettings = new JsonSerializerSettings
{
    ContractResolver = contractResolver,
    Formatting = Formatting.Indented
};

string json = JsonConvert.SerializeObject(person, jsonSerializerSettings);

This will convert all property names to camel case unless overridden by the `[JsonProperty]` attribute.

3. Using a Custom Contract Resolver

If you need more dynamic control over property names, you can implement a custom contract resolver. This allows you to rename properties at runtime without modifying the original class.

Here's a simplified example of how you might implement a custom resolver to rename properties:

csharp
public class CustomContractResolver : DefaultContractResolver
{
    private readonly Dictionary> _renames;

    public CustomContractResolver(Dictionary> renames)
    {
        _renames = renames;
    }

    protected override JsonProperty CreateProperty(MemberInfo member, MemberSerialization memberSerialization)
    {
        var property = base.CreateProperty(member, memberSerialization);

        if (_renames.TryGetValue(property.DeclaringType, out var typeRenames) &&
            typeRenames.TryGetValue(property.PropertyName, out var newPropertyName))
        {
            property.PropertyName = newPropertyName;
        }

        return property;
    }
}

You can then use this resolver to serialize objects with custom property names:

csharp
var renames = new Dictionary>
{
    { typeof(Person), new Dictionary
        {
            { "FirstName", "first_name" },
            { "LastName", "last_name" }
        }
    }
};

var contractResolver = new CustomContractResolver(renames);
var jsonSerializerSettings = new JsonSerializerSettings
{
    ContractResolver = contractResolver,
    Formatting = Formatting.Indented
};

string json = JsonConvert.SerializeObject(person, jsonSerializerSettings);

This approach allows for dynamic renaming without modifying the original class, making it useful for scenarios where property names need to be adjusted based on external conditions.