Question

为模型添加控制器时，生成的操作将类似于此

public ActionResult Edit(int id = 0)
{
    Entity entity = db.Entities.Find(id);
    if (entity == null)
    {
        return HttpNotFound();
    }
    return View(entity);
}

现在在我的情况下，我采用字符串ID，可以通过多种方式映射到DB ID ，从而生成几行代码以检索正确的实体。将代码复制并粘贴到每个采用id来检索实体的动作都感觉非常不优雅。

将检索代码放在控制器的私有函数中可以减少重复代码的数量，但我仍然留下这个：

var entity = GetEntityById(id);
if (entity == null)
    return HttpNotFound();

有没有办法在属性中执行查找并将实体传递给操作？来自python，这可以通过装饰器轻松实现。我设法通过实现IOperationBehavior来为WCF服务做类似的事情，但仍然感觉不那么直截了当。由于通过id检索实体是您经常需要做的事情，我希望除了复制和粘贴代码之外还有其他方法。

理想情况下，它看起来像这样：

[EntityLookup(id => db.Entities.Find(id))]
public ActionResult Edit(Entity entity)
{
    return View(entity);
}

其中EntityLookup采用将string id映射到Entity的任意函数，并返回HttpNotFound或以检索到的实体作为参数调用该操作。

Answer 1

您可以编写自定义ActionFilter：

public class EntityLookupAttribute : ActionFilterAttribute
{
    public override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        // retrieve the id parameter from the RouteData
        var id = filterContext.HttpContext.Request.RequestContext.RouteData.Values["id"] as string;
        if (id == null)
        {
            // There was no id present in the request, no need to execute the action
            filterContext.Result = new HttpNotFoundResult();
        }

        // we've got an id, let's query the database:
        var entity = db.Entities.Find(id);
        if (entity == null)
        {
            // The entity with the specified id was not found in the database
            filterContext.Result = new HttpNotFoundResult();
        }

        // We found the entity => we could associate it to the action parameter

        // let's first get the name of the action parameter whose type matches
        // the entity type we've just found. There should be one and exactly
        // one action argument that matches this query, otherwise you have a 
        // problem with your action signature and we'd better fail quickly here
        string paramName = filterContext
            .ActionDescriptor
            .GetParameters()
            .Single(x => x.ParameterType == entity.GetType())
            .ParameterName;

        // and now let's set its value to the entity
        filterContext.ActionParameters[paramName] = entity;
    }
}

然后：

[EntityLookup]
public ActionResult Edit(Entity entity)
{
    // if we got that far the entity was found
    return View(entity);
}

Answer 2

如果您要重复相似的代码，则可以使用扩展方法。

public static class ControllerExtensions
{
    public static ActionResult StandardEdit<TEntity>(
        this Controller controller, 
        DbContext db, 
        long id)
        where TEntity : class
    {
        TEntity entity = db.Set<TEntity>().Find(id);
        if (entity == null)
        {
            return controller.HttpNotFound();
        }
        return controller.View(entity);
    }
}

public ActionResult Edit(long id = 0)
{
    return this.StandardEdit<Client>(db, id);
}

如果你真的多次重复完全相同的代码，那么这应该通过继承来解决。

创建一个继承自Controller

的通用控制器

public class StandardController : Controller
{
    public ActionResult Edit<TEntity>(long id = 0)
        where TEntity : class
    {
        TEntity entity = db.Set<TEntity>().Find(id);
        if (entity == null)
        {
            return HttpNotFound();
        }
        return View(entity);
    }
}

并将模型控制器更改为从此新控制器继承：

public class ClientController : StandardController
{
    public ActionResult Edit(long id = 0)
    {
        return base.Edit<Client>(id);
    }
}

自动将实体传递给Controller Action

2 个答案: