c# - 启动后更改MVC6的路由集合

Question

在 MVC-5 中，我可以在初始启动后通过访问 RouteTable.Routes 来编辑 routetable。我希望在 MVC-6 中做同样的事情，这样我就可以在运行时添加/删除路由(对 CMS 很有用)。

在 MVC-5 中执行此操作的代码是:

using (RouteTable.Routes.GetWriteLock())
{
    RouteTable.Routes.Clear();

    RouteTable.Routes.IgnoreRoute("{resource}.axd/{*pathInfo}");
    RouteTable.Routes.MapRoute(
        name: "Default",
        url: "{controller}/{action}/{id}",
        defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
    );
}

但是我在 MVC-6 中找不到 RouteTable.Routes 或类似的东西。知道如何在运行时更改路由集合吗？

---

我想使用这个原理来添加，例如，在 CMS 中创建页面时添加一个额外的 url。

如果你有这样的类:

public class Page
{
    public int Id { get; set; }
    public string Url { get; set; }
    public string Html { get; set; }
}

还有一个 Controller ，如:

public class CmsController : Controller
{
    public ActionResult Index(int id)
    {
        var page = DbContext.Pages.Single(p => p.Id == id);
        return View("Layout", model: page.Html);
    }
}

然后，当一个页面被添加到数据库时，我重新创建了 routecollection:

var routes = RouteTable.Routes;
using (routes.GetWriteLock())
{
    routes.Clear();
    foreach(var page in DbContext.Pages)
    {
        routes.MapRoute(
            name: Guid.NewGuid().ToString(),
            url: page.Url.TrimEnd('/'),
            defaults: new { controller = "Cms", action = "Index", id = page.Id }
        );
    }

    var defaultRoute = routes.MapRoute(
        name: "Default",
        url: "{controller}/{action}/{id}",
        defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
    );
}

通过这种方式，我可以将不属于约定或严格模板的页面添加到 CMS。我可以添加一个带有 url /contact 的页面，也可以添加一个带有 url /help/faq/how-does-this-work 的页面。

Answer 1

答案是没有合理的方法来做到这一点，即使找到了方法也不是好的做法。

解决问题的错误方法

基本上，过去 MVC 版本的路由配置就像一个 DI 配置——也就是说，你把所有东西都放在 composition root 中。然后在运行时使用该配置。问题是您可以在运行时将对象推送到配置中(许多人这样做)，这不是正确的方法。

现在配置已经被真正的 DI 容器所取代，这种方法将不再有效。注册步骤现在只能在应用程序启动时完成。

正确的方法

自定义路由的正确方法远远超出 Route类在过去的 MVC 版本中可以做的是 inherit RouteBase或路线。

AspNetCore(以前称为 MVC 6)具有类似的抽象，IRouter和 INamedRouter扮演同样的角色。很像它的前身，IRouter只有两种方法可以实现。

namespace Microsoft.AspNet.Routing
{
    public interface IRouter
    {
        // Derives a virtual path (URL) from a list of route values
        VirtualPathData GetVirtualPath(VirtualPathContext context);

        // Populates route data (including route values) based on the
        // request
        Task RouteAsync(RouteContext context);
    }
}

此接口(interface)是您实现路由的双向特性的地方 - 用于路由值的 URL 和用于路由值的 URL。

一个例子:CachedRoute<TPrimaryKey>

这是一个跟踪和缓存主键到 URL 的 1-1 映射的示例。它是通用的，我已经测试过无论主键是 int 它都有效。或 Guid .

有一个可插拔 block 必须注入(inject)，ICachedRouteDataProvider可以实现对数据库的查询。您还需要提供 Controller 和操作，因此该路由足够通用，可以通过使用多个实例将多个数据库查询映射到多个操作方法。

using Microsoft.AspNetCore.Routing;
using Microsoft.Extensions.Caching.Memory;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using System.Threading.Tasks;

public class CachedRoute<TPrimaryKey> : IRouter
{
    private readonly string _controller;
    private readonly string _action;
    private readonly ICachedRouteDataProvider<TPrimaryKey> _dataProvider;
    private readonly IMemoryCache _cache;
    private readonly IRouter _target;
    private readonly string _cacheKey;
    private object _lock = new object();

    public CachedRoute(
        string controller, 
        string action, 
        ICachedRouteDataProvider<TPrimaryKey> dataProvider, 
        IMemoryCache cache, 
        IRouter target)
    {
        if (string.IsNullOrWhiteSpace(controller))
            throw new ArgumentNullException("controller");
        if (string.IsNullOrWhiteSpace(action))
            throw new ArgumentNullException("action");
        if (dataProvider == null)
            throw new ArgumentNullException("dataProvider");
        if (cache == null)
            throw new ArgumentNullException("cache");
        if (target == null)
            throw new ArgumentNullException("target");

        _controller = controller;
        _action = action;
        _dataProvider = dataProvider;
        _cache = cache;
        _target = target;

        // Set Defaults
        CacheTimeoutInSeconds = 900;
        _cacheKey = "__" + this.GetType().Name + "_GetPageList_" + _controller + "_" + _action;
    }

    public int CacheTimeoutInSeconds { get; set; }

    public async Task RouteAsync(RouteContext context)
    {
        var requestPath = context.HttpContext.Request.Path.Value;

        if (!string.IsNullOrEmpty(requestPath) && requestPath[0] == '/')
        {
            // Trim the leading slash
            requestPath = requestPath.Substring(1);
        }

        // Get the page id that matches.
        TPrimaryKey id;

        //If this returns false, that means the URI did not match
        if (!GetPageList().TryGetValue(requestPath, out id))
        {
            return;
        }

        //Invoke MVC controller/action
        var routeData = context.RouteData;

        // TODO: You might want to use the page object (from the database) to
        // get both the controller and action, and possibly even an area.
        // Alternatively, you could create a route for each table and hard-code
        // this information.
        routeData.Values["controller"] = _controller;
        routeData.Values["action"] = _action;

        // This will be the primary key of the database row.
        // It might be an integer or a GUID.
        routeData.Values["id"] = id;

        await _target.RouteAsync(context);
    }

    public VirtualPathData GetVirtualPath(VirtualPathContext context)
    {
        VirtualPathData result = null;
        string virtualPath;

        if (TryFindMatch(GetPageList(), context.Values, out virtualPath))
        {
            result = new VirtualPathData(this, virtualPath);
        }

        return result;
    }

    private bool TryFindMatch(IDictionary<string, TPrimaryKey> pages, IDictionary<string, object> values, out string virtualPath)
    {
        virtualPath = string.Empty;
        TPrimaryKey id;
        object idObj;
        object controller;
        object action;

        if (!values.TryGetValue("id", out idObj))
        {
            return false;
        }

        id = SafeConvert<TPrimaryKey>(idObj);
        values.TryGetValue("controller", out controller);
        values.TryGetValue("action", out action);

        // The logic here should be the inverse of the logic in 
        // RouteAsync(). So, we match the same controller, action, and id.
        // If we had additional route values there, we would take them all 
        // into consideration during this step.
        if (action.Equals(_action) && controller.Equals(_controller))
        {
            // The 'OrDefault' case returns the default value of the type you're 
            // iterating over. For value types, it will be a new instance of that type. 
            // Since KeyValuePair<TKey, TValue> is a value type (i.e. a struct), 
            // the 'OrDefault' case will not result in a null-reference exception. 
            // Since TKey here is string, the .Key of that new instance will be null.
            virtualPath = pages.FirstOrDefault(x => x.Value.Equals(id)).Key;
            if (!string.IsNullOrEmpty(virtualPath))
            {
                return true;
            }
        }
        return false;
    }

    private IDictionary<string, TPrimaryKey> GetPageList()
    {
        IDictionary<string, TPrimaryKey> pages;

        if (!_cache.TryGetValue(_cacheKey, out pages))
        {
            // Only allow one thread to poplate the data
            lock (_lock)
            {
                if (!_cache.TryGetValue(_cacheKey, out pages))
                {
                    pages = _dataProvider.GetPageToIdMap();

                    _cache.Set(_cacheKey, pages,
                        new MemoryCacheEntryOptions()
                        {
                            Priority = CacheItemPriority.NeverRemove,
                            AbsoluteExpirationRelativeToNow = TimeSpan.FromSeconds(this.CacheTimeoutInSeconds)
                        });
                }
            }
        }

        return pages;
    }

    private static T SafeConvert<T>(object obj)
    {
        if (typeof(T).Equals(typeof(Guid)))
        {
            if (obj.GetType() == typeof(string))
            {
                return (T)(object)new Guid(obj.ToString());
            }
            return (T)(object)Guid.Empty;
        }
        return (T)Convert.ChangeType(obj, typeof(T));
    }
}

CmsCachedRouteDataProvider

这是数据提供程序的实现，基本上是您需要在 CMS 中执行的操作。

public interface ICachedRouteDataProvider<TPrimaryKey>
{
    IDictionary<string, TPrimaryKey> GetPageToIdMap();
}

public class CmsCachedRouteDataProvider : ICachedRouteDataProvider<int>
{
    public IDictionary<string, int> GetPageToIdMap()
    {
        // Lookup the pages in DB
        return (from page in DbContext.Pages
                select new KeyValuePair<string, int>(
                    page.Url.TrimStart('/').TrimEnd('/'),
                    page.Id)
                ).ToDictionary(pair => pair.Key, pair => pair.Value);
    }
}

用法

这里我们在默认路由之前添加路由，并配置其选项。

// Add MVC to the request pipeline.
app.UseMvc(routes =>
{
    routes.Routes.Add(
        new CachedRoute<int>(
            controller: "Cms",
            action: "Index",
            dataProvider: new CmsCachedRouteDataProvider(), 
            cache: routes.ServiceProvider.GetService<IMemoryCache>(), 
            target: routes.DefaultHandler)
        {
            CacheTimeoutInSeconds = 900
        });

    routes.MapRoute(
        name: "default",
        template: "{controller=Home}/{action=Index}/{id?}");

    // Uncomment the following line to add a route for porting Web API 2 controllers.
    // routes.MapWebApiRoute("DefaultApi", "api/{controller}/{id?}");
});

这就是它的要点。您仍然可以稍微改进一下。

我个人会使用工厂模式并将存储库注入(inject) CmsCachedRouteDataProvider 的构造函数中而不是硬编码DbContext例如，无处不在。