将对象存储在会话变量中

Null 发表于 Dev

空值

我有一个下拉菜单，当您选择一个选项值时，请提交表单，并避免重复的数据库调用，我将非敏感对象存储在会话中。

private List<Employee> stafflist
{
    get { return Session["stafflist"] as List<Employee>; }
    set { Session["stafflist"] = new Employee(); }
}
private void RemoveStaff()
{
    Session.Remove("stafflist");
}

但是在我的

[HttpPost]
public ActionResult index (...)
{
    //why can't I get the list of staff like this?
    ViewBag.staff=stafflist.Where(..).toList();

    //is the below still needed? i thought i 
    //have a session variable declare above, 
    //and to avoid 30x repetitive db calls? 
    //also note when i include the below the code runs fine, 
    //however, if i take it out it doesn't. i would like to avoid repetitive db calls
    stafflist=db.Employee.toList(); 
}

CodeCaster

首先，您不应该阻止查询数据库。正确的缓存很难正确实现，并且数据库完全能够执行查询和缓存数据。

如果您绝对确定要绕过数据库，并查询客户端（即在控制器中），则需要从数据库中至少每个访问者一次提取整个人员列表。

您可以在对该控制器的第一个GET调用中执行此操作，假设用户将始终访问该控件：

[HttpGet]
public ActionResult Index (...)
{
    var cachedStaff = db.Employee.toList(); 
    Session["stafflist"] = cachedStaff;
}

然后在POST中，您实际上要执行数据库查询（同样，考虑让数据库执行其擅长的工作），您可以从会话中查询列表：

[HttpPost]
public ActionResult Index (...)
{
    var cachedStaff = Session["stafflist"] as List<Employee>();

    // TODO: check cachedStaff for null, for when someone posts after 
    // their session expires or didn't visit the Index page first.

    var selectedStaff = cachedStaff.Where(..).ToList();

    // the rest of your code
}

然后，您引入的属性可以用作语法糖来稍微清理一下代码：

private List<Employee> CachedStaff
{
    get { return Session["stafflist"] as List<Employee>; }
    set { Session["stafflist"] = value; }
}

[HttpGet]
public ActionResult Index (...)
{
    CachedStaff = db.Employee.toList(); 
}

[HttpPost]
public ActionResult Index (...)
{
    // TODO: this will throw an ArgumentNullException when
    //  the staff list is not cached, see above.
    var selectedStaff = CachedStaff.Where(..).ToList();

    // the rest of your code
}