如何在asp.net mvc中合并数据库访问和缓存（非静态字段，方法或属性“ Module.dbApp”需要对象引用）

Question

This is actually 2 questions in one.

I have an asp.net mvc application where I have to load a list of Modules, its just a simple list with ID, modulename and a class name to render it on the view with font awesome.

My model is like this:

   public class Module
    {
        [Key]
        public int Id { get; set; }
        public string ModuleName { get; set; }
        public string FontAwesomeClass { get; set; }
    }

Because the module list is a Partial View that will render some icons on the top navigation bar, I dont want that for each refresh of the app, it goes to the DB, so it must be cached(I am using Azure REDIS Cache, not relevant for the question anyway), so instead of calling the DB context directly from the controller, I am calling a Cache Class that will check if the cache object exists, if not it will retrieve it from DB, if it does, it will return it from cache.

This my solution structure: http://screencast.com/t/uayPYiHaPCav

Here is my controller Module.cs

public ActionResult GetModules()
    {
        return View(Cache.Module.GetModules());
    }

As you can see the Controller does not have any logic where to get the data from.

Here is the Module.cs (on the Cache Namespace)

public class Module
    {
        private AppDataContext dbApp = new AppDataContext();

        //Load modules from cache or from database
        public static List<Models.Module> GetModules()
        {
            IDatabase cache = Helper.Connection.GetDatabase();
            List<Models.Module> listOfModules = (List<Models.Module>)cache.Get("Modules");
            if (listOfModules == null)
            {
                return dbApp.ModuleList.ToList();
            }
            else
            {
                return listOfModules;
            }
        }           
    }

Here I have a compiler error which I am not sure how to best fix it:

Error CS0120 An object reference is required for the non-static field, method, or property 'Module.dbApp'

So that was my first question.

The 2nd question is more about the design pattern, do you consider this correct or not? the way I am trying to get the data from Cache, and its actually the Cache class which checks if data is on it or if it has to go to the DB.

Answer 1

First Question: make your private member static

private static AppDataContext dbApp = new AppDataContext();

2nd Question: your cache strategy seems pretty standard. The only thing is that you might want to expire cache data. For example, the cached data can get old and the longer it stays in the cache the older it gets. You might at some point want to expire it and get fresh data again.

Update:

@EstebanV for code sample (this off the top of my head, don't assume that it compiles):

/** 
     ICachedPersonDao abstracts away the caching mechanism 
     away from the core of your application 
**/
public CachedPersonDao : ICachedPersonDao
    {

      private IPersonDao personDao = null;

      public CachedPersonDao(IPersonDao personDao)
      {
          this.personDao = personDao;
      }

      public Person GetPersonById(int id){

          bool isInCache = CACHE.SomeFunctionThatChecksInYourCache(id);
          if (isInCache)
          {
               return CACHE.SomeFunctionThatReturnsTheCachedPerson(id);
          }
          else
          {
               //Well it's not in the cache so let's get it from the DB.
               return this.personDao.GetPersonById(id);
          }
      }
    }

    /** 
       IPersonDao abstracts database communication 
       away from the core of your application 
    **/
    public class PersonDao : IPersonDao
    {
          public Person GetPersonById(int id)
          {
                /** Get the person by id from the DB 
                   through EntityFramework or whatever 
                 **/
          }
    }

Usage:

In your controller, use ICachedPersonDao if you want to attempt to get from cache or use IPersonDao if you want to get it directly from the database without checking the cache.

Like I said, you should learn Dependency Injection it will help "inject" these dependencies into the classes that uses them.

I say again, this is off the top of my head. It won't compile. It's just to illustrate the concept.