5

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，在我的例子中，我采用了一个字符串 id，它可以通过多种方式映射到 DB ID，生成几行代码来检索正确的实体。将该代码复制并粘贴到每个需要 id 来检索实体的操作中感觉非常不雅。

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，但我仍然剩下这个：

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仍然感觉不那么直接的 WCF 服务来做类似的事情。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);
}

whereEntityLookup将任意函数映射string id到Entity并返回HttpNotFound或调用以检索到的实体作为参数的操作。

4

2 回答 2

3

您可以编写一个自定义 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;
    }
}

接着：

[EntityLookup]
public ActionResult Edit(Entity entity)
{
    // if we got that far the entity was found
    return View(entity);
}
于 2013-02-25T15:49:50.400 回答
0

如果您重复类似的代码，那么您可以使用扩展方法。

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);
}

如果您确实多次重复完全相同的代码，那么这应该通过继承来解决。

创建一个继承自的通用控制器Controller

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);
    }
}

并将您的模型控制器更改为从这个新控制器继承：

public class ClientController : StandardController
{
    public ActionResult Edit(long id = 0)
    {
        return base.Edit<Client>(id);
    }
}
于 2013-02-25T15:58:47.047 回答