/// <summary>
		/// Adds a new Navigation Path.
		/// </summary>
		/// <param name="transaction">A database transaction.</param>
		/// <param name="nspace">The target namespace (<c>null</c> for the root).</param>
		/// <param name="name">The Name of the Path.</param>
		/// <param name="pages">The Pages array.</param>
		/// <returns>The correct <see cref="T:NavigationPath"/> object.</returns>
		private NavigationPath AddNavigationPath(DbTransaction transaction, string nspace, string name, PageInfo[] pages) {
			ICommandBuilder builder = GetCommandBuilder();
			QueryBuilder queryBuilder = new QueryBuilder(builder);

			string query, finalQuery = "";
			List<Parameter> parameters = new List<Parameter>(3 * pages.Length);
			int count = 0;
			string countString;

			foreach(PageInfo page in pages) {
				countString = count.ToString();

				query = queryBuilder.InsertInto("NavigationPath", new string[] { "Name", "Namespace", "Page", "Number" },
					new string[] { "Name" + countString, "Namespace" + countString, "Page" + countString, "Number" + countString });

				parameters.Add(new Parameter(ParameterType.String, "Name" + countString, name));
				parameters.Add(new Parameter(ParameterType.String, "Namespace" + countString, nspace));
                parameters.Add(new Parameter(ParameterType.String, "Page" + countString, NameTools.GetLocalName(page.FullName)??" " ));
				parameters.Add(new Parameter(ParameterType.Int32, "Number" + countString, (short)count));

				finalQuery = queryBuilder.AppendForBatch(finalQuery, query);
                
				count++;
			}

            finalQuery = queryBuilder.BuildBatchCommand(finalQuery);
			DbCommand command = builder.GetCommand(transaction, finalQuery, parameters);

            int rows = ExecuteNonQuery(command, false,true,count);

			if(rows == pages.Length) {
				NavigationPath result = new NavigationPath(NameTools.GetFullName(nspace, name), this);
				result.Pages = Array.ConvertAll<PageInfo, string>(pages, (x) => { return x.FullName; });
				return result;
			}
			else return null;
		}
		/// <summary>
		/// Clears the index.
		/// </summary>
		/// <param name="state">A state object passed from the index.</param>
		private void ClearIndex(object state) {
			// state can be null, depending on when the method is called

			ICommandBuilder builder = GetCommandBuilder();
			QueryBuilder queryBuilder = new QueryBuilder(builder);

			string query = queryBuilder.DeleteFrom("IndexWordMapping");
			query = queryBuilder.AppendForBatch(query, queryBuilder.DeleteFrom("IndexWord"));
			query = queryBuilder.AppendForBatch(query, queryBuilder.DeleteFrom("IndexDocument"));
            query= queryBuilder.BuildBatchCommand(query);

            DbCommand command = null;
            if (state == null) command = builder.GetCommand(connString, query, new List<Parameter>());
            else command = builder.GetCommand((DbTransaction)state, query, new List<Parameter>());

			ExecuteNonQuery(command, state == null);
		}
		/// <summary>
		/// Removes all messages for a page and stores the new messages.
		/// </summary>
		/// <param name="page">The page.</param>
		/// <param name="messages">The new messages to store.</param>
		/// <returns><c>true</c> if the messages are stored, <c>false</c> otherwise.</returns>
		/// <exception cref="ArgumentNullException">If <paramref name="page"/> or <paramref name="messages"/> are <c>null</c>.</exception>
		public bool BulkStoreMessages(PageInfo page, Message[] messages) {
			if(page == null) throw new ArgumentNullException("page");
			if(messages == null) throw new ArgumentNullException("messages");

			ICommandBuilder builder = GetCommandBuilder();
			DbConnection connection = builder.GetConnection(connString);
			DbTransaction transaction = BeginTransaction(connection);

			if(GetPage(transaction, page.FullName) == null) {
				RollbackTransaction(transaction);
				return false;
			}

			foreach(Message msg in GetMessages(transaction, page)) {
				UnindexMessageTree(page, msg, transaction);
			}

			string nspace, name;
			NameTools.ExpandFullName(page.FullName, out nspace, out name);
			if( string.IsNullOrEmpty(nspace)||string.IsNullOrEmpty(nspace.Trim())) nspace = " ";

			QueryBuilder queryBuilder = new QueryBuilder(builder);

			string query = queryBuilder.DeleteFrom("Message");
			query = queryBuilder.Where(query, "Page", WhereOperator.Equals, "Page");
			query = queryBuilder.AndWhere(query, "Namespace", WhereOperator.Equals, "Namespace");

			List<Parameter> parameters = new List<Parameter>(2);
			parameters.Add(new Parameter(ParameterType.String, "Page", name));
			parameters.Add(new Parameter(ParameterType.String, "Namespace", nspace));

			DbCommand command = builder.GetCommand(transaction, query, parameters);

			ExecuteNonQuery(command, false);

			List<Message> allMessages;
			List<int> parents;

			UnTreeMessages(messages, out allMessages, out parents, -1);

			string finalQuery = "";
			int count = 1;
			string countString;
			parameters = new List<Parameter>(MaxStatementsInBatch * 8);

			int rowsDone = 0;

			for(int i = 0; i < allMessages.Count; i++) {
				// Execute the batch in smaller chunks

				Message msg = allMessages[i];
				int parent = parents[i];

				countString = count.ToString();

				query = queryBuilder.InsertInto("Message", new string[] { "Page", "Namespace", "Id", "Parent", "Username", "Subject", "DateTime", "Body" },
					new string[] { "Page" + countString, "Namespace" + countString, "Id" + countString, "Parent" + countString, "Username" + countString, "Subject" + countString, "DateTime" + countString, "Body" + countString });

				parameters.Add(new Parameter(ParameterType.String, "Page" + countString, name));
				parameters.Add(new Parameter(ParameterType.String, "Namespace" + countString, nspace));
				parameters.Add(new Parameter(ParameterType.Int16, "Id" + countString, (short)msg.ID));
				if(parent != -1) parameters.Add(new Parameter(ParameterType.Int16, "Parent" + countString, parent));
				else parameters.Add(new Parameter(ParameterType.Int16, "Parent" + countString, DBNull.Value));
				parameters.Add(new Parameter(ParameterType.String, "Username" + countString, msg.Username));
				parameters.Add(new Parameter(ParameterType.String, "Subject" + countString, msg.Subject));
				parameters.Add(new Parameter(ParameterType.DateTime, "DateTime" + countString, msg.DateTime));
				parameters.Add(new Parameter(ParameterType.String, "Body" + countString, msg.Body));

				finalQuery = queryBuilder.AppendForBatch(finalQuery, query);

				count++;

				if(count == MaxStatementsInBatch) {
                    finalQuery = queryBuilder.BuildBatchCommand(finalQuery);
					command = builder.GetCommand(transaction, finalQuery, parameters);

                    rowsDone += ExecuteNonQuery(command, false, true, count); 

					finalQuery = "";
					count = 1;
					parameters.Clear();
				}
			}

			if(finalQuery.Length > 0) {
				command = builder.GetCommand(transaction, finalQuery, parameters);

                rowsDone += ExecuteNonQuery(command, false, true, count); 
			}

			if(rowsDone == allMessages.Count) {
				foreach(Message msg in messages) {
					IndexMessageTree(page, msg, transaction);
				}
				CommitTransaction(transaction);
				return true;
			}
			else {
				RollbackTransaction(transaction);
				return false;
			}
		}
		/// <summary>
		/// Binds a Page with one or more Categories.
		/// </summary>
		/// <param name="connection">A database connection.</param>
		/// <param name="page">The Page to bind.</param>
		/// <param name="categories">The Categories to bind the Page with.</param>
		/// <returns>True if the binding succeeded.</returns>
		/// <remarks>After a successful operation, the Page is bound with all and only the categories passed as argument.</remarks>
		private bool RebindPage(DbConnection connection, PageInfo page, string[] categories) {
			string nspace, name;
			NameTools.ExpandFullName(page.FullName, out nspace, out name);
			if( string.IsNullOrEmpty(nspace)||string.IsNullOrEmpty(nspace.Trim())) nspace = " ";

			ICommandBuilder builder = GetCommandBuilder();
			QueryBuilder queryBuilder = new QueryBuilder(builder);

			string query = queryBuilder.DeleteFrom("CategoryBinding");
			query = queryBuilder.Where(query, "Page", WhereOperator.Equals, "Page");
			query = queryBuilder.AndWhere(query, "Namespace", WhereOperator.Equals, "Namespace");

			List<Parameter> parameters = new List<Parameter>(2);
			parameters.Add(new Parameter(ParameterType.String, "Page", name));
			parameters.Add(new Parameter(ParameterType.String, "Namespace", nspace));

			DbCommand command = builder.GetCommand(connection, query, parameters);

			int rows = ExecuteNonQuery(command, false);

			if(rows < 0) return false;

			if(categories.Length > 0) {
				string finalQuery = "";
				parameters = new List<Parameter>(categories.Length * 3);
				int count = 0;
				string countString;

				foreach(string cat in categories) {
					countString = count.ToString();

					query = queryBuilder.InsertInto("CategoryBinding", new string[] { "Namespace", "Category", "Page" },
						new string[] { "Namespace" + countString, "Category" + countString, "Page" + countString });
					finalQuery = queryBuilder.AppendForBatch(finalQuery, query);

					parameters.Add(new Parameter(ParameterType.String, "Namespace" + countString, nspace));
					parameters.Add(new Parameter(ParameterType.String, "Category" + countString, NameTools.GetLocalName(cat)));
					parameters.Add(new Parameter(ParameterType.String, "Page" + countString, name));

					count++;
				}
                finalQuery = queryBuilder.BuildBatchCommand(finalQuery);
				command = builder.GetCommand(connection, finalQuery, parameters);

                rows = ExecuteNonQuery(command, false, true, count);

				return rows == categories.Length;
			}
			else return true;
		}
		/// <summary>
		/// Deletes all data associated to a document.
		/// </summary>
		/// <param name="document">The document.</param>
		/// <param name="state">A state object passed from the index (can be <c>null</c> or a <see cref="T:DbTransaction" />).</param>
		private void DeleteDataForDocument(IDocument document, object state) {
			// 1. Delete all data related to a document
			// 2. Delete all words that have no more mappings

			ICommandBuilder builder = GetCommandBuilder();
			QueryBuilder queryBuilder = new QueryBuilder(builder);

			string query = queryBuilder.DeleteFrom("IndexDocument");
			query = queryBuilder.Where(query, "Name", WhereOperator.Equals, "DocName");
			List<Parameter> parameters = new List<Parameter>(1);
			parameters.Add(new Parameter(ParameterType.String, "DocName", document.Name));

			string subQuery = queryBuilder.SelectFrom("IndexWordMapping", new string[] { "Word" });
			subQuery = queryBuilder.GroupBy(subQuery, new string[] { "Word" });
			string query2 = queryBuilder.DeleteFrom("IndexWord");
			query2 = queryBuilder.WhereNotInSubquery(query2, "IndexWord", "Id", subQuery);

			query = queryBuilder.AppendForBatch(query, query2);
            query = queryBuilder.BuildBatchCommand(query);
			DbCommand command = null;
			if(state != null) command = builder.GetCommand((DbTransaction)state, query, parameters);
			else command = builder.GetCommand(connString, query, parameters);

			// Close only if state is null
			ExecuteNonQuery(command, state == null);
		}
		/// <summary>
		/// Stores the content for a revision.
		/// </summary>
		/// <param name="transaction">A database transaction.</param>
		/// <param name="content">The content.</param>
		/// <param name="revision">The revision.</param>
		/// <returns><c>true</c> if the content is stored, <c>false</c> otherwise.</returns>
		private bool SetContent(DbTransaction transaction, PageContent content, int revision) {
			string name, nspace;
			NameTools.ExpandFullName(content.PageInfo.FullName, out nspace, out name);
			if( string.IsNullOrEmpty(nspace)||string.IsNullOrEmpty(nspace.Trim())) nspace = " ";

			ICommandBuilder builder = GetCommandBuilder();
			QueryBuilder queryBuilder = new QueryBuilder(builder);

			string query = queryBuilder.InsertInto("PageContent",
				new string[] { "Page", "Namespace", "Revision", "Title", "User", "LastModified", "Comment", "Content", "Description" },
				new string[] { "Page", "Namespace", "Revision", "Title", "User", "LastModified", "Comment", "Content", "Description" });

			List<Parameter> parameters = new List<Parameter>(9);
			parameters.Add(new Parameter(ParameterType.String, "Page", name));
			parameters.Add(new Parameter(ParameterType.String, "Namespace", nspace));
			parameters.Add(new Parameter(ParameterType.Int16, "Revision", revision));
			parameters.Add(new Parameter(ParameterType.String, "Title", content.Title));
			parameters.Add(new Parameter(ParameterType.String, "User", content.User));
			parameters.Add(new Parameter(ParameterType.DateTime, "LastModified", content.LastModified));
			if(!string.IsNullOrEmpty(content.Comment)) parameters.Add(new Parameter(ParameterType.String, "Comment", content.Comment));
			else parameters.Add(new Parameter(ParameterType.String, "Comment", DBNull.Value));
			parameters.Add(new Parameter(ParameterType.String, "Content", content.Content));
			if(!string.IsNullOrEmpty(content.Description)) parameters.Add(new Parameter(ParameterType.String, "Description", content.Description));
			else parameters.Add(new Parameter(ParameterType.String, "Description", DBNull.Value));

			DbCommand command = builder.GetCommand(transaction, query, parameters);

			int rows = ExecuteNonQuery(command, false);

			if(rows != 1) return false;

			if(content.Keywords.Length > 0) {
				parameters = new List<Parameter>(content.Keywords.Length * 4);
				string fullQuery = "";
				int count = 0;
				string countString;
				foreach(string kw in content.Keywords) {
					countString = count.ToString();

					query = queryBuilder.InsertInto("PageKeyword", new string[] { "Page", "Namespace", "Revision", "Keyword" },
						new string[] { "Page" + countString, "Namespace" + countString, "Revision" + countString, "Keyword" + countString });
					fullQuery = queryBuilder.AppendForBatch(fullQuery, query);

					parameters.Add(new Parameter(ParameterType.String, "Page" + countString, name));
					parameters.Add(new Parameter(ParameterType.String, "Namespace" + countString, nspace));
					parameters.Add(new Parameter(ParameterType.Int16, "Revision" + countString, revision));
					parameters.Add(new Parameter(ParameterType.String, "Keyword" + countString, kw));

					count++;
				}
                fullQuery = queryBuilder.BuildBatchCommand(fullQuery);
				command = builder.GetCommand(transaction, fullQuery, parameters);

                rows = ExecuteNonQuery(command, false, true, count);

				return rows == content.Keywords.Length;
			}
			else return true;
		}
		/// <summary>
		/// Merges two Categories.
		/// </summary>
		/// <param name="source">The source Category.</param>
		/// <param name="destination">The destination Category.</param>
		/// <returns>The correct <see cref="T:CategoryInfo" /> object.</returns>
		/// <remarks>The destination Category remains, while the source Category is deleted, and all its Pages re-bound 
		/// in the destination Category.</remarks>
		/// <exception cref="ArgumentNullException">If <paramref name="source"/> or <paramref name="destination"/> are <c>null</c>.</exception>
		public CategoryInfo MergeCategories(CategoryInfo source, CategoryInfo destination) {
			if(source == null) throw new ArgumentNullException("source");
			if(destination == null) throw new ArgumentNullException("destination");

			// 1. Check for same namespace
			// 2. Load all pages in source
			// 3. Load all pages in destination
			// 4. Merge lists in memory
			// 5. Delete all destination bindings
			// 6. Delete source cat
			// 7. Insert new bindings stored in memory

			string sourceNs = NameTools.GetNamespace(source.FullName);
			string destinationNs = NameTools.GetNamespace(destination.FullName);
			
			// If one is null and the other not null, fail
			if(sourceNs == null && destinationNs != null || sourceNs != null && destinationNs == null) return null;
			else {
				// Both non-null or both null
				if(sourceNs != null) {
					// Both non-null, check names
					NamespaceInfo tempSource = new NamespaceInfo(sourceNs, this, null);
					NamespaceInfo tempDest = new NamespaceInfo(destinationNs, this, null);
					// Different names, fail
					if(new NamespaceComparer().Compare(tempSource, tempDest) != 0) return null;
				}
				// else both null, OK
			}

			string nspace = sourceNs != null ? sourceNs : " ";

			ICommandBuilder builder = GetCommandBuilder();
			DbConnection connection = builder.GetConnection(connString);
			DbTransaction transaction = BeginTransaction(connection);

			CategoryInfo actualSource = GetCategory(transaction, source.FullName);
			CategoryInfo actualDestination = GetCategory(transaction, destination.FullName);

			if(actualSource == null) {
				RollbackTransaction(transaction);
				return null;
			}
			if(actualDestination == null) {
				RollbackTransaction(transaction);
				return null;
			}

			string destinationName = NameTools.GetLocalName(actualDestination.FullName);

			string[] mergedPages = MergeArrays(actualSource.Pages, actualDestination.Pages);

			QueryBuilder queryBuilder = new QueryBuilder(builder);

			string query = queryBuilder.DeleteFrom("CategoryBinding");
			query = queryBuilder.Where(query, "Namespace", WhereOperator.Equals, "Namespace");
			query = queryBuilder.AndWhere(query, "Category", WhereOperator.Equals, "Category");

			List<Parameter> parameters = new List<Parameter>(2);
			parameters.Add(new Parameter(ParameterType.String, "Namespace", nspace));
			parameters.Add(new Parameter(ParameterType.String, "Category", destinationName));

			DbCommand command = builder.GetCommand(transaction, query, parameters);

			int rows = ExecuteNonQuery(command, false);

			if(rows == -1) {
				RollbackTransaction(transaction);
				return null;
			}

			if(!RemoveCategory(transaction, source)) {
				RollbackTransaction(transaction);
				return null;
			}

			string finalQuery = "";
			parameters = new List<Parameter>(MaxStatementsInBatch * 3);
			rows = 0;
			int count = 1;
			string countString;

			foreach(string page in mergedPages) {
				// This batch is executed in small chunks (MaxStatementsInBatch) to avoid exceeding DB's max batch length/size

				countString = count.ToString();

				query = queryBuilder.InsertInto("CategoryBinding", new string[] { "Namespace", "Category", "Page" },
					new string[] { "Namespace" + countString, "Category" + countString, "Page" + countString });
				finalQuery = queryBuilder.AppendForBatch(finalQuery, query);

				parameters.Add(new Parameter(ParameterType.String, "Namespace" + countString, nspace));
				parameters.Add(new Parameter(ParameterType.String, "Category" + countString, destinationName));
				parameters.Add(new Parameter(ParameterType.String, "Page" + countString, NameTools.GetLocalName(page)));

				count++;

				if(count == MaxStatementsInBatch) {
					// Batch is complete -> execute
                    finalQuery = queryBuilder.BuildBatchCommand(finalQuery);
					command = builder.GetCommand(transaction, finalQuery, parameters);
                    rows += ExecuteNonQuery(command, false, true, count);

					count = 1;
					finalQuery = "";
					parameters.Clear();
				}
			}

			if(finalQuery.Length > 0) {
				// Execute remaining queries, if any
				command = builder.GetCommand(transaction, finalQuery, parameters);
                rows += ExecuteNonQuery(command, false, true, count);
			}

			if(rows == mergedPages.Length) {
				CommitTransaction(transaction);
				CategoryInfo result = new CategoryInfo(actualDestination.FullName, this);
				result.Pages = mergedPages;
				return result;
			}
			else {
				RollbackTransaction(transaction);
				return null;
			}
		}