~/posts/injecting-jsonserializeroptions-in-.net-core-3

If you're using .NET Core 3, you're probably relying on it to serialize and deserialize your models to and from JSON. One of the great things about that is you can easily configure the serializer in one place and it will use those options wherever it serializes or deserializes your models.

For example, you could configure it to automatically deserialize enum values for you:

// Startup.cs
services.AddControllers().AddJsonOptions(opt =>
{
    opt.JsonSerializerOptions.Converters.Add(new JsonStringEnumConverter());
});

Now this is great and all, but what if you need to do some custom serializing outside of the .NET pipeline? Ideally, we could use the same serializer options to make sure we get consistent results throughout our project.

First of all, it's worth noting that the way the System.Text.Json library is designed, the serializer (JsonSerializer) is a static class that cannot be instanced. Therefore, we cannot access a serializer instance that is configured with our options. Instead, we need to have access to the options object itself, and pass it in to the serializer (e.g. JsonSerializer.Serialize(myJsonString, myJsonSerializerOptions)).

Fortunately, there's an easy—though not well documented—way of injecting the JsonSerializerOptions:

// MyController.cs
private readonly JsonSerializerOptions _jsonSerializerOptions;

public MyController(IOptions<JsonOptions> jsonOptions)
{
    _jsonSerializerOptions = jsonOptions.Value.JsonSerializerOptions;
}

public IActionResult MyAction()
{
    // ...
    JsonSerializer.Serialize(someJson, _jsonSerializerOptions);
    // ...
}

This is great although a little unintuitive. We can clean it up a bit by adding a service provider for JsonSerializerOptions directly to our container:

// Startup.cs
services.AddControllers().AddJsonOptions(opt =>
{
    // configure our JsonSerializerOptions
});

services.AddSingleton(provider =>
    provider.GetService<IOptions<JsonOptions>>().Value.JsonSerializerOptions);

Now we can directly inject JsonSerializerOptions!

// MyController.cs
private readonly JsonSerializerOptions _jsonSerializerOptions;

public MyController(JsonSerializerOptions jsonSerializerOptions)
{
    _jsonSerializerOptions = jsonSerializerOptions;
}

public IActionResult MyAction()
{
    // ...
    JsonSerializer.Serialize(someJson, _jsonSerializerOptions);
    // ...
}
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