IdentityMap.cs

using System;
using System.Collections.Generic;
using System.Text;
using System.Collections;
using Havit.Diagnostics.Contracts;

namespace Havit.Business;

/// <summary>
/// Identity map pro business-objekty.
/// </summary>
public class IdentityMap
{
	/// <summary>
	/// Hashtable obsahující hashtable pro každý typ.
	/// </summary>
	private readonly Dictionary<Type, Dictionary<int, WeakReference>> types;

	/// <summary>
	/// Vytvoří instanci třídy <see cref="IdentityMap"/>.
	/// </summary>
	public IdentityMap()
	{
		types = new Dictionary<Type, Dictionary<int, WeakReference>>();
	}

	/// <summary>
	/// Uloží business-objekt do identity-map.
	/// </summary>
	/// <param name="businessObject">business objekt</param>
	public void Store(BusinessObjectBase businessObject)
	{
		Contract.Requires<ArgumentNullException>(businessObject != null, nameof(businessObject));
		Contract.Requires<ArgumentException>(!businessObject.IsNew, "businessObject ukládaný do IdentityMap nesmí být nový.");

		Type businessObjectType = businessObject.GetType();
		Dictionary<int, WeakReference> typeDictionary;
		if (!types.TryGetValue(businessObjectType, out typeDictionary))
		{
			typeDictionary = new Dictionary<int, WeakReference>();
			types.Add(businessObjectType, typeDictionary);
		}

		WeakReference reference;
		if (typeDictionary.TryGetValue(businessObject.ID, out reference))
		{
			if (reference.Target != null)
			{
				if (!Object.ReferenceEquals(reference.Target, businessObject))
				{
					throw new InvalidOperationException("V IdentityMap je již jiná instance tohoto objektu.");
				}
			}
			else
			{
				reference.Target = businessObject;
			}
		}
		else
		{
			typeDictionary.Add(businessObject.ID, new WeakReference(businessObject));
		}
	}

	/// <summary>
	/// Načte business-objekt z identity-map.
	/// </summary>
	/// <typeparam name="T">typ business objektu</typeparam>
	/// <param name="id">ID business objektu</param>
	/// <param name="target">cíl, kam má být business-objekt načten</param>
	/// <returns><c>true</c>, pokud se podařilo načíst; <c>false</c>, pokud objekt v identity-map není (target pak obsahuje <c>null</c>)</returns>
	public bool TryGet<T>(int id, out T target)
		where T : BusinessObjectBase
	{
		Dictionary<int, WeakReference> typeDictionary;
		if (!types.TryGetValue(typeof(T), out typeDictionary))
		{
			target = null;
			return false;
		}

		WeakReference reference;
		if (!typeDictionary.TryGetValue(id, out reference))
		{
			target = null;
			return false;
		}

		target = (T)reference.Target;
		return (target != null);
	}

	/// <summary>
	/// Vrátí business-objekt z identity-map.
	/// </summary>
	/// <typeparam name="T">typ business objektu</typeparam>
	/// <param name="id">ID business objektu</param>
	/// <returns>business-objekt z identity-map; <c>null</c>, pokud v ní není</returns>
	public T Get<T>(int id)
		where T : BusinessObjectBase
	{
		Dictionary<int, WeakReference> typeDictionary;
		if (!types.TryGetValue(typeof(T), out typeDictionary))
		{
			return null;
		}

		WeakReference reference;
		if (!typeDictionary.TryGetValue(id, out reference))
		{
			return null;
		}

		return (T)reference.Target;
	}
}