Hi, I'm building a custom content app with a custom table inside Umbraco's database:

    [PluginController("MyApi")]
    [UmbracoApplicationAuthorize(Constants.Applications.Content)]
    public class MyApiController : UmbracoAuthorizedApiController
    {
        private readonly IUmbracoContextAccessor _umbracoContext;
        private readonly IContentTypeService _contentTypeService;
        private readonly IDataTypeService _dataTypeService;
        private readonly IPublishedContentCache _contentCache;

        private readonly IScopeProvider _scopeProvider;


        public MyApiController() { }

        public MyApiController(IUmbracoContextAccessor umbracoContext,
            IContentTypeService contentTypeService,
            IDataTypeService dataTypeService,
            IPublishedContentCache contentCache)
        {
            _umbracoContext = umbracoContext;
            _contentTypeService = contentTypeService;
            _dataTypeService = dataTypeService;
            _contentCache = contentCache;
        }

        private IEnumerable<MyModel> DoSomethingThatMightBeUseful(int nodeId)
        {
            IEnumerable<MyModel> result = null;
            try
            {
                using (var scope = Current.ScopeProvider.CreateScope())
                {
                    result = scope.Database.Fetch<MyModel>("SELECT * FROM table");

                    scope.Complete();
                }

            } catch {}

            return result;
        }
    }

Everything was going fine until I stumbled upon this comment: https://our.umbraco.com/forum/umbraco-8/96075-alternative-solution-to-use-applicationcontextcurrentdatabasecontextdatabase-in-umbraco-8#comment-303960

So I switched from Current.ScopeProvider.CreateScope() to injecting IScopeProvider inside the constructor, like so:

    [PluginController("MyApi")]
    [UmbracoApplicationAuthorize(Constants.Applications.Content)]
    public class MyApiController : UmbracoAuthorizedApiController
    {
        private readonly IUmbracoContextAccessor _umbracoContext;
        private readonly IContentTypeService _contentTypeService;
        private readonly IDataTypeService _dataTypeService;
        private readonly IPublishedContentCache _contentCache;

        private readonly IScopeProvider _scopeProvider;


        public MyApiController() { }

        public MyApiController(IUmbracoContextAccessor umbracoContext,
            IContentTypeService contentTypeService,
            IDataTypeService dataTypeService,
            IPublishedContentCache contentCache,
            IScopeProvider scopeProvider)
        {
            _umbracoContext = umbracoContext;
            _contentTypeService = contentTypeService;
            _dataTypeService = dataTypeService;
            _contentCache = contentCache;
            _scopeProvider = scopeProvider;
        }

        private IEnumerable<MyModel> DoSomethingThatMightBeUseful(int nodeId)
        {
            IEnumerable<MyModel> result = null;
            try
            {
                using (var scope = _scopeProvider.CreateScope())
                {
                    result = scope.Database.Fetch<MyModel>("SELECT * FROM table");

                    scope.Complete();
                }

            } catch {}

            return result;
        }
    }

And that's when the problems began: something was not working properly. Went into debug mode, and discovered that _scopeProvider is null.

So since it was not a random person that made the comment that made me switch to DI, clearly i'm missing something.