ASP.NET MVC 5如何自动加载未显式引用的jQuery Validation？

Hey there! Great question—this is actually a result of ASP.NET MVC 5's built-in bundling and section rendering features, which are easy to miss if you're just scanning the _Layout.cshtml file directly. Let me break it down step by step:

1. The Bundle Configuration #

First, take a look at the BundleConfig.cs file in your project's App_Start folder. This is where MVC defines script and style bundles, and it includes a pre-configured bundle for jQuery validation:

bundles.Add(new ScriptBundle("~/bundles/jqueryval").Include(
    "~/Scripts/jquery.validate*"));

The wildcard jquery.validate* matches both jquery.validate.js and jquery.validate.unobtrusive.js (since their filenames start with jquery.validate). MVC will bundle these two scripts together into a single request when the bundle is rendered.

2. Section Rendering in Scaffolded Views #

The reason you don't see a direct <script> tag in _Layout.cshtml is that the validation scripts are loaded on-demand in specific views, using MVC's section system:

• Scaffolded views that include forms (like Create.cshtml or Edit.cshtml) will have a Scripts section at the bottom, which looks something like this:

  @section Scripts {
      @Scripts.Render("~/bundles/jqueryval")
  }
  

• Your _Layout.cshtml file includes a line that renders this section (usually near the bottom of the page, after the jQuery script tag):

  @RenderSection("Scripts", required: false)
  

When the page loads, MVC injects the content from the view's Scripts section into the layout at the location of @RenderSection, which is why you see the validation scripts in Chrome's Sources tab even though they're not directly in _Layout.cshtml.

Alternatively, some scaffolded views might use the helper method @Html.ValidationScripts() instead—this is just a shorthand that renders the same ~/bundles/jqueryval bundle under the hood.

3. Why This Approach? #

MVC uses this pattern to optimize performance: instead of loading validation scripts on every page (even those without forms), it only loads them on pages that actually need form validation. This reduces unnecessary network requests and speeds up page loads for non-form pages.

内容的提问来源于stack exchange，提问作者Tom Baxter