在存在Cache.insert的地方进行添加迁移或更新数据库失败

Question

I am trying to run the add-migration command and get this error:

PM> add-migration LatestModel
System.NullReferenceException: Object reference not set to an instance of an object.

which is erroring on this line of code:

 public static string WebText(string key)
    {
        //Is value in cache?
        string outputValue;
        if (!CacheHelper.Get(key, out outputValue))
        {
            var str = StringsService.GetResource(value);

           HttpContext.Current.Cache.Insert(
           key,
           outputValue,
           null,
           System.Web.Caching.Cache.NoAbsoluteExpiration,
           TimeSpan.FromMinutes(60));

            return str;

        }

        return outputValue;
    }

Now, the function WebText just gets a value out of a database table, however, I cant see why entity framework is trying to scaffold or do anything with the HttpContect line.

error thrown

System.NullReferenceException: Object reference not set to an instance of an object.
at PL_AnnexA_Application.Models.Helpers.WebtextHelpers.WebText(String key) in
Helpers.cs:line 36   
at System.ComponentModel.DisplayNameAttribute.GetHashCode()
at System.Collections.Generic.ObjectEqualityComparer`1.GetHashCode(T obj)
at System.Linq.Set`1.InternalGetHashCode(TElement value)
at System.Linq.Set`1.Find(TElement value, Boolean add)
at System.Linq.Enumerable.<ExceptIterator>d__99`1.MoveNext()
at System.Linq.Enumerable.<OfTypeIterator>d__aa`1.MoveNext()
Line 36 is

HttpContext.Current.Cache.Insert(

Any ideas?

Answer 1

Looks like you are overriding a GetHashCode() method somewhere in an attribute and are calling your WebText method in it. The hashcode is probably used somewhere internally by EF when doing a migration. And yes, your current http context will be NULL at that moment since it probably executes at the Application_Start in the global asax.

One solution is to remove your override of GetHashCode and solve your necessity for it elsewhere.

The GetHashCode appears in your stacktrace.

Answer 2

As I really need the cache functionalty and the displaytext override, I realised just check if HttpContect.Current is not null in the cache routine and that does the job. I blame the 15 hours coding today. thanks Anshul for the pointer.