Mvc: AddMvc builder calls redundancy

[stevejgordon]

This may be more a query than an issue. I've been looking at the source, specifically the AddMvc extension method.

Part of the code looks like this

builder.AddViews();
builder.AddRazorViewEngine();
builder.AddRazorPages();
builder.AddCacheTagHelper();

// +1 order
builder.AddDataAnnotations(); // +1 order

Within AddRazorViewEngine it calls AddViews. Therefore, why do we call AddViews first. Seems redundant? Am I missing a reason, other than this method being a bit more explicit about what it's adding?

In addition, AddDataAnnotations is called within AddViews. Therefore, calling it explicitly later on also seems redundant? It seems that the lines above could actually be reduced to the following, and still perform equally.

builder.AddRazorViewEngine();
builder.AddRazorPages();
builder.AddCacheTagHelper();

Interested to understand the design decisions here?

[rynowak]

The AddXyz methods automatically add their dependencies because it's much friendlier that way.

this method being a bit more explicit about what it's adding

That's exactly the reason. Someone would be asking the opposite question if we pared it down to the 'minimal' set of AddXyz calls.

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Breaking up the monolith into pieces was complex and sometimes forced us into some inelegant choices. I think I'll still be answering questions on this for the rest of my life 👍

[stevejgordon]

Thanks @rynowak and that makes sense. Appreciate the answer. I'm writing a blog about the AddMvcCore and AddMvc methods so it's good to know the reason.

[Eilon]

Send us a link when you post it!

[stevejgordon]

@Eilon - Sure, here is the first part - https://www.stevejgordon.co.uk/asp-net-core-mvc-anatomy-addmvccore - Hopefully it's all accurate!

[stevejgordon]

And this post features @rynowak's quick feedback! - https://www.stevejgordon.co.uk/asp-net-core-anatomy-part-2-addmvc

[rynowak]

These are great posts, love them both!

A little more info about the ApplicationPartManager. It's complicated because of the methods like AddControllersAsServices(). This methods go discover all of the controllers (or tag helpers or view components) and then register them with the service collection. This means that ApplicationPartManager needs to be 'baked' before services are available, which is a significant challenge in our system.

The other complication is that the ApplicationPartManager needs to be customizable in our tests. We have a bunch of test websites for functional testing for MVC and we want to make sure in our tests that the controllers from each website don't leak into the other websites' tests. See https://github.com/aspnet/Mvc/blob/dev/test/Microsoft.AspNetCore.Mvc.FunctionalTests/MvcTestFixture.cs for the juicy bit.

[stevejgordon]

Thanks @rynowak - I really appreciate the feedback and additional info. I'll take a look at those extra links.