Model Validation should mention `ModelState.AddModelError`

[jfoshee]

aspnetcore/mvc/models/validation.md may be the first page someone reads about validation. Yet it seems to miss the simplest method to return a validation error to the user (where built-in attributes fall short): ModelState.AddModelError.

This method makes it particularly easy, for example, if the validation needs to check a database

if (dbContext.Records.Any(record => record.Name == model.Name))
{
    ModelState.AddModelError("Name", "The Name is already in use.");
    return View(model);
}

The existing documentation leads the reader to believe that creating a custom ValidationAttribute or implementing IValidatableObject are the only alternatives to built-in attributes.

Thanks for your consideration!

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Document Details

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• ID: 0156ffc3-47ac-d5da-fbc2-9ff5018b071b
• Version Independent ID: 615db388-a244-41f7-21b5-a4085d9ed479
• Content: Model validation in ASP.NET Core MVC
• Content Source: aspnetcore/mvc/models/validation.md
• Product: aspnet-core
• Technology: aspnetcore-mvc
• GitHub Login: @Rick-Anderson
• Microsoft Alias: riande

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Associated WorkItem - 64069

[Rick-Anderson]

@jfoshee you're right. It should also show how to add a model error to the model, not the property:

ModelState.AddModelError(string.Empty, "My error message");

Code goes with dotnet/AspNetCore.Docs.Samples#110