How to get value list from generic dictionary

Question

I've used this ObjectPool class as the basis of my Identity Map. However, I need to bring back the list of all objects of a type. Matthew has :

    public IEnumerable<T> GetItems<T>()
    {
        Type myType = typeof(T);

        if (!m_pool.ContainsKey(myType))
            return new T[0];

        return m_pool[myType].Values as IEnumerable<T>;
    }

However, when I make changes to the client like so:

        pool.AddItem<Animal>(dog.ID, dog);
        pool.AddItem<Vegetable>(carrot.Identifier, carrot);
        pool.AddItem<Vegetable>(greenbean.Identifier, greenbean);
        pool.AddItem<Mineral>(carbon.UniqueID, carbon);

        Console.WriteLine("Dog is in the pool -- this statement is " + pool.ContainsKey<Animal>(dog.ID));

        IEnumerable<Vegetable> veggies = pool.GetItems<Vegetable>();
        foreach(Vegetable veg in veggies)
            Console.WriteLine(string.Format("{0} - {1}", veg.Color, veg.IsTasty));

veggies is null. It would appear that m_pool[myType].Values does not support the cast to IEnumerable.

I've tried a few things, for example:

        IDictionary<int, T> dic = (IDictionary<int, T>) m_pool[myType];
        ICollection<T> values = (ICollection<T>)dic.Values;

However, I always end up with a casting error.

What am I missing?

Answer 1

What type exaclty is carrot and greenbean? Can you post your Add<>() method?

Answer 2

Well, that GetItems method is never going to work, seeing as Dictionary<int, object>.Values doesn't implement IEnumerable<T> unless T is object. Shame that the method is so fundamentally broken - oh for some unit tests.

I suggest you check the licence, and if you can fix GetItems, do so:

public IEnumerable<T> GetItems<T>()
{
    Type myType = typeof(T);

    IDictionary<int, object> dictionary;

    if (!m_pool.TryGetValue(myType, out dictionary))
    {
        return new T[0];
    }

    return dictionary.Values.Cast<T>();
}

That's if you're using .NET 3.5 (you'll need using System.Linq as well, to get the Cast extension method). Let me know if you need something for .NET 2.0.

Answer 3

I use the following ObjectPool ( the code is not mine I just added couple of methods ) ( if you do not use log4net replace logger.Info with Console.WriteLine ; )

using System;
using System.Collections.Generic;
using System.Text;
using System.Collections.Specialized;
using System.Reflection;
using log4net;
using log4net.Config; 


namespace DH
{

 //DH - DataHolders
 /// <summary>
 /// This class models a storage structure for objects queriable by id 
 /// </summary>
 public class ObjectPool
 {

  #region Props
  private int totalCount;
  public int TotalCount
  {
   get
   {
    return totalCount;
   }
  }

  public int ID { get; set; }


  #endregion Props


  public ObjectPool ()
  {
   m_pool = new Dictionary<Type, Dictionary<Int32, Object>> ();
  }


  private Dictionary<Type, Dictionary<Int32, Object>> m_pool;

  public void AddItem<T> ( Int32 pID, T value )
  {
   Type myType = typeof ( T );

   if (!m_pool.ContainsKey ( myType ))
   {
    m_pool.Add ( myType, new Dictionary<int, object> () );
    m_pool[myType].Add ( pID, value );

    totalCount++;
    return;
   }

   if (!m_pool[myType].ContainsKey ( pID ))
   {
    m_pool[myType].Add ( pID, value );
    totalCount++;
    return;
   }

   m_pool[myType][pID] = value;
   totalCount++;
   //Utils.Debugger.WriteIf("Adding 1 to pool count , pool count is " + this.totalCount);
  }


  public void AddItem<T> ( T value )
  {
   Int32 pID = totalCount ;
   Type myType = typeof ( T );

   if (!m_pool.ContainsKey ( myType ))
   {
    m_pool.Add ( myType, new Dictionary<int, object> () );
    m_pool[myType].Add ( pID, value );

    totalCount++;
    return;
   }

   if (!m_pool[myType].ContainsKey ( pID ))
   {
    m_pool[myType].Add ( pID, value );
    totalCount++;
    return;
   }

   m_pool[myType][pID] = value;
   totalCount++;
   //Utils.Debugger.WriteIf("Adding 1 to pool count , pool count is " + this.totalCount);
  }


  public bool RemoveItem<T> ( Int32 pID )
  {
   Type myType = typeof ( T );

   if (!m_pool.ContainsKey ( myType ))
    return false;

   if (!m_pool[myType].ContainsKey ( pID ))
    return false;

   totalCount--;
   return m_pool[myType].Remove ( pID );
  }

  public bool ContainsKey<T> ( Int32 pID )
  {
   Type myType = typeof ( T );

   if (!m_pool.ContainsKey ( myType ))
    return false;

   if (!m_pool[myType].ContainsKey ( pID ))
    return false;

   return m_pool[myType].ContainsKey ( pID );
  }

  public IEnumerable<T> GetItems<T> ()
  {
   Type myType = typeof ( T );

   if (!m_pool.ContainsKey ( myType ))
    return new T[0];

   return m_pool[myType].Values as IEnumerable<T>;
  }


  /// <summary>
  /// Gets the item.
  /// </summary>
  /// <typeparam name="T"></typeparam>
  /// <param name="pID">The p ID.</param>
  /// <returns></returns>
  /// <exception cref="KeyNotFoundException"></exception>
  public T GetItem<T> ( Int32 pID )
  {
   // will throw KeyNotFoundException if either of the dictionaries 
   // does not hold the required key
   return (T)m_pool[typeof ( T )][pID];
  }


  /// <summary>
  /// 
  /// </summary>
  /// <typeparam name="T"></typeparam>
  /// <param name="strPropMetaName"> the string representation of the </param>
  /// <param name="strPropValue"></param>
  /// <returns></returns>
  public T GetItemByPropertyValue<T> ( String strPropMetaName , String strPropValue)
  {
   Type myType = typeof ( T );

   for (int i = 0; i < this.TotalCount; i++)
   {
    if (!m_pool.ContainsKey ( myType ))
    {
     return default ( T );
    }
    else
    {
     if (this.ContainsKey<T> ( i ))
     {
      //get an item object having the same type
      T item = this.GetItem<T> ( i );

      //if the object has the same property -- check its value
      MemberInfo[] members = myType.GetMembers ();
      for (int j = 0; j < members.Length; j++)
      {
       logger.Info ( "members[j].Name is " + members[j].Name );
       //logger.Info ( ".MemberType.ToString() " + members[j].MemberType.ToString () );
       //logger.Info ( "members[j].GetType().ToString() " + members[j].GetType ().ToString () );
       //logger.Info ( " members[j].ToString () is " + members[j].ToString () );
       //logger.Info ( " members[j].ToString () is " + members[j] );


       if (members[j].Name.ToString ().Equals ( strPropMetaName ))
       {


        FieldInfo[] fi;
        fi = myType.GetFields ( BindingFlags.Public | BindingFlags.NonPublic | BindingFlags.Instance );


        foreach (FieldInfo f in fi)
        {
         //logger.Info ( "f.GetValue( obj ) is " + f.GetValue ( item ) );
         if ( f.GetValue ( item ).ToString().Equals(strPropValue))
          return (T)m_pool[typeof ( T )][i];
         else 
          continue ;

        } //eof foreach        
       }
       else
        continue;
      } //eof for j

     } //eof if 
     else
      continue;
    } //eof else if m_pool.ContainsKey
   }
   return default ( T );
  }


  private static readonly ILog logger =
LogManager.GetLogger ( typeof ( DH.ObjectPool ) );

 } //eof class pool 

} //eof namespace



namespace PoolSample
{
 class Program
 {
  private static readonly ILog logger =
LogManager.GetLogger ( typeof ( Program ) );

  public static DH.ObjectPool pool = new DH.ObjectPool ();

  static void Main ( string[] args )
  {
   DOMConfigurator.Configure (); //tis configures the logger 

   Animal dog = new Animal () { Name = "Fido", ID = 1 };
   Vegetable carrot = new Vegetable { Color = "Orange", Identifier = 2, IsTasty = true };
   Mineral carbon = new Mineral () { UniqueID = 3, IsPoisonousToAnimal = false , Name="some"};
   HolderForStrings hfs = new HolderForStrings () { ID = 4, Value = "user_name", MetaName = "meta_nam" };
   HolderForStrings hfs1 = new HolderForStrings () { ID = 5, Value = "user_name", MetaName = "hfs1" };
   Mineral carbon1 = new Mineral () { UniqueID = 3, IsPoisonousToAnimal = false, Name = "some1" };

   pool.AddItem ( dog );
   pool.AddItem ( carrot );
   pool.AddItem ( hfs );
   pool.AddItem ( hfs1 );


   //pool.AddItem<Animal>(dog.ID, dog);
   //pool.AddItem<Vegetable>(carrot.Identifier, carrot);
   //pool.AddItem<Mineral> ( carbon );
   //pool.AddItem<HolderForStrings> ( 1, hfs );



   //logger.Info("Dog is in the pool -- this statement is " + pool.ContainsKey<Animal>(dog.ID));
   //logger.Info("hfs is in the pool -- this statement is " + pool.ContainsKey<HolderForStrings>(hfs.ID));
   //logger.Info("The hfs value is from the poos is " + pool.GetItem<HolderForStrings>(4).Value);


   //logger.Info("poo.GetItems is " + pool.GetItems<HolderForStrings>());
   #region while
   //for (int i = 0; i < pool.Count -1 ; i++)
   int i = 1;
   do
   {
    try
    {
     logger.Info ( "counting" );
     logger.Info ( " i is " + i.ToString () );
     if (pool.ContainsKey<Animal> ( i ))
     {
      logger.Info ( " I see animal which is " + pool.GetItem<Animal> ( i ).Name );
     }

     if (pool.ContainsKey<Vegetable> ( i ))
     {
      logger.Info ( " I see Vegetable which is " + pool.GetItem<Vegetable> ( i ).Color );
     }


     if (pool.ContainsKey<Mineral> ( i ))
     {
      logger.Info ( " I see Mineral which is " + pool.GetItem<Mineral> ( i ).IsPoisonousToAnimal );
     }


     if (pool.ContainsKey<HolderForStrings> ( i ))
     {
      logger.Info ( " I see string which is " + pool.GetItem<HolderForStrings> ( i ).Value );
     }

     //logger.Info("pool.GetItem<HolderForStrings>(4).Value); is " + pool.GetItem<Object>(i).ToString());

     i = i + 1;
    }
    catch (KeyNotFoundException e)
    {
     continue;
    }

   } //eof for 
   while (i < pool.TotalCount);
#endregion while
   #region AddHolders
   ////this is the success identifier
   //HoldInt16 holdVerifier = new HoldInt16()
   //{
   //  ID=0 ,
   //  MetaName = "ret",
   //  Value = 0
   //};
   //pool.AddItem<HoldInt16>(holdVerifier.ID, holdVerifier);

   //ListDictionary lidMetaName = pool.LidMetaName;
   ////this is the message
   //HoldString holdMsg = new HoldString( ref lidMetaName)
   //{
   //  ID=1,
   //  MetaName = "msg",
   //  Value = msg,
   //  Title = "title" 
   //};
   //pool.AddItem<HoldString>(holdMsg.ID, holdMsg);


   //HoldString holdmmsg = new HoldString(ref lidMetaName)
   //{
   //  ID=2,
   //  MetaName = "mmsg",
   //  Value = "mmsg" , 
   //  Title = "title" 
   //};
   #endregion AddHolders


   //Utils.Debugger.DebugListDictionary(ref msg, "domainName", ref lidMetaName);

   //get the value be metaName

   logger.Info ( "I queried the pool by property with meta Value and value user_name " );

   HolderForStrings HolderForStrings = pool.GetItemByPropertyValue<HolderForStrings> ( "MetaName", "hfs1" );
   //logger.Info ( "object dump" + Utils.Log.ObjDumper.DumpObject ( HolderForStrings ) );
   logger.Info ( "I found the following value for property with the name \"Name\" " );
   logger.Info ( HolderForStrings.MetaName);

   Console.ReadLine ();







  } //eof Main

 } //eof class 

 public class Animal
 {
  public Int32 ID { get; set; }
  public String Name { get; set; }
 }

 public class HolderForStrings
 {
  public Int32 ID { get; set; }
  public String Value { get; set; }
  public String MetaName { get; set; }
  Type ObjType = typeof ( string );
  public Int32 Size { get; set; }
  public bool IsOptional { get; set; }
  public bool IsPrimaryKey { get; set; }

 } //eof class


 public class Vegetable
 {
  public Int32 Identifier { get; set; }
  public String Color { get; set; }
  public Boolean IsTasty { get; set; }
 }

 public class Mineral
 {
  public Int32 UniqueID { get; set; }
  public Boolean IsPoisonousToAnimal { get; set; }
  public String Name { get; set; } 
 }

 #region classObjectPool
 //public class ObjectPool
 //{
 //  public int Count
 //  {
 //    get { return m_pool.Count; }
 //  }

 //  public ObjectPool ()
 //  {
 //    m_pool = new Dictionary<Type, Dictionary<Int32, Object>> ();
 //  }

 //  private Dictionary<Type, Dictionary<Int32, Object>> m_pool;

 //  public void AddItem<T> ( Int32 pID, T value )
 //  {
 //    Type myType = typeof ( T );

 //    if (!m_pool.ContainsKey ( myType ))
 //    {
 //      m_pool.Add ( myType, new Dictionary<int, object> () );
 //      m_pool[myType].Add ( pID, value );
 //      return;
 //    }

 //    if (!m_pool[myType].ContainsKey ( pID ))
 //    {
 //      m_pool[myType].Add ( pID, value );
 //      return;
 //    }

 //    m_pool[myType][pID] = value;
 //  }

 //  public bool RemoveItem<T> ( Int32 pID )
 //  {
 //    Type myType = typeof ( T );

 //    if (!m_pool.ContainsKey ( myType ))
 //      return false;

 //    if (!m_pool[myType].ContainsKey ( pID ))
 //      return false;

 //    return m_pool[myType].Remove ( pID );
 //  }

 //  public bool ContainsKey<T> ( Int32 pID )
 //  {
 //    Type myType = typeof ( T );

 //    if (!m_pool.ContainsKey ( myType ))
 //      return false;

 //    if (!m_pool[myType].ContainsKey ( pID ))
 //      return false;

 //    return m_pool[myType].ContainsKey ( pID );
 //  }

 //  public IEnumerable<T> GetItems<T> ()
 //  {
 //    Type myType = typeof ( T );

 //    if (!m_pool.ContainsKey ( myType ))
 //      return new T[0];

 //    return m_pool[myType].Values as IEnumerable<T>;
 //  }

 //  /// <summary>
 //  /// Gets the item.
 //  /// </summary>
 //  /// <typeparam name="T"></typeparam>
 //  /// <param name="pID">The p ID.</param>
 //  /// <returns></returns>
 //  /// <exception cref="KeyNotFoundException"></exception>
 //  public T GetItem<T> ( Int32 pID )
 //  {
 //    // will throw KeyNotFoundException if either of the dictionaries 
 //    // does not hold the required key
 //    return (T)m_pool[typeof ( T )][pID];
 //  }

 //} //eof pool  
 #endregion

 public enum EnumType : byte
 {
  String,
  Int32,
  Boolean
 }
} //eof program