Identity Map Design Pattern

Identity Map Design Pattern.cs

public abstract class BaseEntity
{
    // Default identity(key) for Each Object
    public int Id { get; set; }

    // Basic properties
    public DateTime CreateDate { get; set; }
    public DateTime UpdateDate{ get; set; }
    public bool IsActive { get; set; }
}

public class Account
        :BaseEntity
{

}

public class IdentityMap<TObject>
{
    Hashtable entities = new Hashtable();
    
    // in here the key is identity properties (such as Id,AccountNumber etc.)
    public TObject GetById(int key)
    {
        if (entities.ContainsKey(key))
            return (TObject)entities[key];
        else
            return default(TObject);
    }

    public void Add(TObject entity,int key)
    {
        if (!entities.Contains(key))
            entities.Add(key, entity);
    }
}

public interface IAccountRepository<TObject>
{
    // Espeacially for find methods 
    // Cause These methods just returns a single object

    //IQueryable<TObject> All();
    //IQueryable<TObject> Filter(Expression<Func<TObject, bool>> predicate);
    //IQueryable<TObject> Filter<Key>(Expression<Func<TObject, bool>> filter,
    //   out int total, int index = 0, int size = 50);        
    TObject Find(int keys);
    TObject Find(Expression<Func<TObject, bool>> predicate);
    //bool Contains(Expression<Func<TObject, bool>> predicate);


    //TObject Create(TObject t);
    //int Delete(TObject t);
    //int Delete(Expression<Func<TObject, bool>> predicate);
    //int Update(TObject t);
}

public class AccountRepository
    :IAccountRepository<Account>
{
    IdentityMap<Account> identityMap;

    public AccountRepository()
    {
        this.identityMap = new IdentityMap<Account>();
    }
    
    // identity Control and identityMap add(like pool mechanism)
    public Account Find(int key)
    {
        Account account = identityMap.GetById(key);
        if (null == account) 
        {
            account = GetById(key);
            if (null != account)
                identityMap.Add(account, account.Id);
        }
        return account;
    }

    // directly get data from database
    public Account GetById(int key)
    {
        Account account = default(Account);
            
        // operations to retrieval of data object from database

        return account;
    }

    public Account Find(Expression<Func<Account, bool>> predicate)
    {
        // Above mapping control process can apply for this method
        return default(Account);
    }
}