Dependency injection example for aspnet core (2.1) Web API action parameters using a custom ContractResolver.

If you need an action parameter to be provided by the DI-container (the ServiceProvider in vanilla aspnet core), you can add the attribute [FromServices] like so:

public async Task<ActionResult<SomeResult>> AddSomething([FromServices] AddSomethingCommand)

(https://docs.microsoft.com/en-us/aspnet/core/mvc/models/model-binding?view=aspnetcore-2.1)

The downside of this is that regular model binding doesn't take place after this. So, anything that's been added to the request body doesn't get bound to AddSomethingCommand.

I've tried to use a custom ModelBinder to get the job done, but was unsuccesful. The following SO question kept me busy quite some time: https://stackoverflow.com/questions/35616035/mvc-6-custom-model-binder-with-dependency-injection

In the end, https://www.newtonsoft.com/json/help/html/DeserializeWithDependencyInjection.htm led me to the following solution, which this repo is the result of.

By overriding CreateObjectContract of CamelCasePropertyNamesContractResolver (any other ContractResolver can be used), this example manages to get an instance from the aspnet core DI-container, after which normal model binding takes place.

Helpful docs / blogposts / SO links:

https://www.newtonsoft.com/json/help/html/DeserializeWithDependencyInjection.htm http://www.dotnetcurry.com/aspnet-mvc/1368/aspnet-core-mvc-custom-model-binding http://www.dotnet-programming.com/post/2017/03/17/Custom-Model-Binding-in-Aspnet-Core-2-Model-Binding-Interfaces.aspx https://stackoverflow.com/questions/35616035/mvc-6-custom-model-binder-with-dependency-injection