Kerosene ORM: a dynamic, configuration-less and self-adaptive ORM for POCO objects supporting a SQL-like syntax from C#

// ======================================================== 
namespace Kerosene.DataServices.Concrete
{
	using Kerosene.DataServices.Agnostic;
	using Kerosene.ORM.Maps;
	using Kerosene.Tools;
	using System;
	using System.Collections;
	using System.Text;

	// ==================================================== 
	/// <summary>
	/// Represents an object able to execute a query command and to return afterwards the entities produced as the
	/// result of that execution.
	/// </summary>
	/// <typeparam name="T">The type of the entities to be produced when the command is executed and enumerated.</typeparam>
	public class DataQueryEnumerator<T> : IDataQueryEnumerator<T> where T : class
	{
		bool _IsDisposed = false;
		DataQuery<T> _DataQuery = null;
		KMetaQueryEnumerator<T> _Enumerator = null;

		/// <summary>
		/// Creates a new enumerator for the given data query.
		/// </summary>
		/// <param name="dataQuery">The data query this enumerator is created for.</param>
		public DataQueryEnumerator(DataQuery<T> dataQuery)
		{
			if ((_DataQuery = dataQuery) == null) throw new ArgumentNullException("dataQuery", "DataQuery cannot be null.");
			if ((_Enumerator = _DataQuery.MetaCommand.GetEnumerator()) == null) throw new CannotCreateException(string.Format("Cannot create enumerator for command '{0}'.", dataQuery));
		}

		/// <summary>
		/// Gets whether this instance has been disposed or not.
		/// </summary>
		public bool IsDisposed
		{
			get { return _IsDisposed; }
		}

		/// <summary>
		/// Disposes this instance.
		/// </summary>
		public void Dispose()
		{
			if (!IsDisposed) { OnDispose(true); GC.SuppressFinalize(this); }
		}

		~DataQueryEnumerator()
		{
			if (!IsDisposed) OnDispose(false);
		}

		protected virtual void OnDispose(bool disposing)
		{
			if (!IsDisposed && disposing)
			{
				if (_Enumerator != null) _Enumerator.Dispose(); _Enumerator = null;
				_DataQuery = null;
			}
			_IsDisposed = true;
		}

		/// <summary>
		/// Returns the string representation of this instance.
		/// </summary>
		public override string ToString()
		{
			StringBuilder sb = new StringBuilder();
			if (IsDisposed) sb.Append("disposed::[");

			sb.Append(_Enumerator == null ? GetType().EasyName() : _Enumerator.ToString());

			if (IsDisposed) sb.Append("]");
			return sb.ToString();
		}

		/// <summary>
		/// Gets the query command this enumerator is associated with.
		/// </summary>
		public DataQuery<T> Command
		{
			get { return _DataQuery; }
		}
		IDataQuery<T> IDataQueryEnumerator<T>.Command
		{
			get { return this.Command; }
		}

		/// <summary>
		/// Gets the current object being enumerated, or null if this command has not been executed yet or if there
		/// are no more records available.
		/// </summary>
		public T Current
		{
			get { return _Enumerator == null ? null : _Enumerator.Current; }
		}
		object IEnumerator.Current
		{
			get { return this.Current; }
		}

		/// <summary>
		/// Executes the command if it has not been executed yet, and tries to retrieve the next available record from
		/// the database. Returns true if a new record is available and can be obtained using the Current property, or
		/// false if there are no more records available.
		/// </summary>
		public bool MoveNext()
		{
			if (IsDisposed) throw new ObjectDisposedException(this.ToString());
			return _Enumerator.MoveNext();
		}

		/// <summary>
		/// Resets this enumerator.
		/// </summary>
		public void Reset()
		{
			if (_Enumerator != null && !_Enumerator.IsDisposed) _Enumerator.Reset();
		}
	}
}
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