C# 在HttpContext.Current.Items缓存中使用lambda表达式查找键
我有一个请求缓存,使用HttpContext.Current.Items实现,如下所示:C# 在HttpContext.Current.Items缓存中使用lambda表达式查找键,c#,lambda,httprequest,C#,Lambda,Httprequest,我有一个请求缓存,使用HttpContext.Current.Items实现,如下所示: private static readonly Lazy<CacheCurrentCall> lazy = new Lazy<CacheCurrentCall>(() => new CacheCurrentCall()); public static CacheCurrentCall Instance { get { IDictiona
private static readonly Lazy<CacheCurrentCall> lazy =
new Lazy<CacheCurrentCall>(() => new CacheCurrentCall());
public static CacheCurrentCall Instance
{
get
{
IDictionary items = HttpContext.Current.Items;
if (!items.Contains("CacheCurrentCall"))
{
items["CacheCurrentCall"] = new CacheCurrentCall();
}
return items["CacheCurrentCall"] as CacheCurrentCall;
}
}
private CacheCurrentCall()
{
}
public void Add<T>(T o, string key, int cacheDurationSeconds = 0)
{
HttpContext.Current.Items.Add(key, o);
}
public void Clear(string key)
{
HttpContext.Current.Items.Remove(key);
}
public bool Exists(string key)
{
return HttpContext.Current.Items[key] != null;
}
public bool Get<T>(string key, out T value)
{
try
{
if (!Exists(key))
{
value = default(T);
return false;
}
value = (T)HttpContext.Current.Items[key];
}
catch
{
value = default(T);
return false;
}
return true;
}
该属性是一个IDictionary
,因此您必须执行以下操作:
public IEnumerable<string> GetKey (Func<string, bool> condition)
{
return HttpContext.Current.Items
.Cast<DictionaryEntry>()
.Where(e => e.Key is string &&
e.Value is string &&
condition(e.Key as string))
.Select(e => e.Value as string);
}
public IEnumerable GetKey(Func条件)
{
返回HttpContext.Current.Items
.Cast()
其中(e=>e.Key是字符串&&
e、 值为字符串&&
条件(如键作为字符串))
.选择(e=>e.值作为字符串);
}
或在查询语法中:
public IEnumerable<string> GetKey (Func<string, bool> condition)
{
return
from e in HttpContext.Current.Items.Cast<DictionaryEntry>()
where e.Key is string &&
e.Value is string &&
condition(e.Key as string)
select e.Value as string;
}
public IEnumerable<string> GetKey (Func<string, bool> condition)
{
return
from k in HttpContext.Current.Items.Keys.OfType<string>()
where condition(k)
select k;
}
public IEnumerable GetKey(Func条件)
{
返回
来自HttpContext.Current.Items.Cast()中的e
其中e.Key是字符串&&
e、 值为字符串&&
条件(例如,键作为字符串)
选择e值作为字符串;
}
更新我错过了阅读问题的机会。我以为您希望根据键的特定标准选择值。如果只想选择关键点,实际上会更容易:
public IEnumerable<string> GetKey (Func<string, bool> condition)
{
return HttpContext.Current.Items.Keys
.OfType<string>()
.Where(condition);
}
public IEnumerable GetKey(Func条件)
{
返回HttpContext.Current.Items.Keys
第()类
.在何处(条件);
}
或在查询语法中:
public IEnumerable<string> GetKey (Func<string, bool> condition)
{
return
from e in HttpContext.Current.Items.Cast<DictionaryEntry>()
where e.Key is string &&
e.Value is string &&
condition(e.Key as string)
select e.Value as string;
}
public IEnumerable<string> GetKey (Func<string, bool> condition)
{
return
from k in HttpContext.Current.Items.Keys.OfType<string>()
where condition(k)
select k;
}
public IEnumerable GetKey(Func条件)
{
返回
从HttpContext.Current.Items.Keys.OfType()中的k开始
何处条件(k)
选择k;
}
您试过什么吗?您自己在实施此解决方案时遇到了哪些问题?您是否收到错误、输出不正确或是什么?谢谢,我最终需要对您的代码做一个小改动(问题不太清楚,是我的错)(请参阅第二次编辑),但它可以工作。@很抱歉,我一开始误解了您的问题。有关更好的解决方案,请参阅我的更新答案。
public IEnumerable<string> GetKey (Func<string, bool> condition)
{
return HttpContext.Current.Items.Keys
.OfType<string>()
.Where(condition);
}
public IEnumerable<string> GetKey (Func<string, bool> condition)
{
return
from k in HttpContext.Current.Items.Keys.OfType<string>()
where condition(k)
select k;
}