Dynamic CRUD controller.

SamplesController.cs

using Microsoft.AspNetCore.Mvc;

namespace Petricords.API.Controllers;

public class SamplesController : ApiController
{
    private readonly IServiceProvider _services;

    public SamplesController(IServiceProvider services)
    {
        _services = services;
    }

    [HttpGet]
    public IReadOnlyList<CrudItemBase> GetAll()
    {
        var test = "some data";
        
        var generic = typeof(CrudItem<>); // CrudItem<>
        var constructed = generic.MakeGenericType(test.GetType()); // CrudItem<string>  
        
        generic = typeof(CrudService<>); // CrudService<> 
        constructed = generic.MakeGenericType(constructed); // CrudService<CrudItem<string>>  
        
        var service = _services.GetRequiredService(constructed);
        var baseService = service as CrudService ?? throw new Exception();
        return baseService.AllItems;
    }

    [HttpPost]
    public CrudItemBase Insert(CrudItem<string> data)
    {
        // this is how we will se the input
        var input = data as CrudItemBase;

        var generic = typeof(CrudService<>); // CrudService<> 
        var constructed = generic.MakeGenericType(input.GetType()); // CrudService<CrudItem<string>>  
        
        var service = _services.GetRequiredService(constructed);
        var baseService = service as CrudService ?? throw new Exception();
        baseService.Add(input);

        return baseService.AllItems.Last();
    }
}

public abstract class CrudService
{
    public abstract void Add(CrudItemBase item);

    public abstract IReadOnlyList<CrudItemBase> AllItems { get; }
}

public class CrudService<T> : CrudService
    where T : CrudItemBase
{
    private readonly List<T> _list = new();

    public void Add(T item) => _list.Add(item);

    public override void Add(CrudItemBase item) => 
        Add(item as T ?? throw new Exception());

    public override IReadOnlyList<CrudItemBase> AllItems => _list.OfType<CrudItemBase>().ToList();
}

public abstract class CrudItemBase {}

public class CrudItem<T> : CrudItemBase
{
    public CrudItem(T value)
    {
        Value = value;
    }

    public T Value { get; } 
}