自动将实体传递给Controller Action

Question

为模型添加控制器时,生成的操作将如下所示

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,我采用一个字符串id,它可以通过多种方式映射到DB ID,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来检索实体的操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减少了重复代码的数量,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.我设法通过实现一个IOperationBehavior仍然感觉不那么简单的WCF服务做类似的事情.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采用任意函数映射string id,Entity并以HttpNotFound检索到的实体作为参数返回或调用操作.

Answer 1

你可以编写一个自定义的 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;
    }
}

进而：

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