added the new DB3-based backend. This is just the beginning, there are

2001-02-11  Rodrigo Moya <rodrigo@ximian.com>

	* pcs/cal-backend-db.[ch]: added the new DB3-based backend. This is just
	the beginning, there are some missing things still.

svn path=/trunk/; revision=8182

1 files changed, 995 insertions, 0 deletions

diff --git a/calendar/pcs/cal-backend-db.c b/calendar/pcs/cal-backend-db.c
new file mode 100644
index 0000000000..0165164e5e
--- /dev/null
+++ b/calendar/pcs/cal-backend-db.c
@@ -0,0 +1,995 @@
+/* Evolution calendar - iCalendar DB backend
+ *
+ * Copyright (C) 2001 Ximian, Inc.
+ *
+ * Author: Rodrigo Moya <rodrigo@ximian.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA 02111-1307, USA.
+ */
+
+#include <config.h>
+#include <gtk/gtkobject.h>
+#include "cal-util/cal-recur.h"
+#include "cal-backend-db.h"
+#include <db.h>
+#if DB_MAJOR_VERSION < 3
+#  error "You need libdb3 to compile the DB backend"
+#endif
+
+/* structure to identify an open cursor */
+typedef struct {
+	DBC* dbc;
+	DB*  parent_db;
+	/* TODO: convert into a hash table */
+	GList* keys;
+	GList* data;
+} CalBackendDBCursor;
+
+/* private part of the CalBackendDB structure */
+struct _CalBackendDBPrivate {
+	/* URI where the calendar data is stored */
+	GnomeVFSURI *uri;
+
+	/* Berkeley DB's library handles */
+	DB *objects_db;
+	DB *history_db;
+
+	/* list of open cursors */
+	GList *cursors;
+
+	/* list of clients using this backend */
+	GList *clients;
+};
+
+static void cal_backend_db_class_init (CalBackendDBClass *klass);
+static void cal_backend_db_init (CalBackendDB *cbdb);
+static void cal_backend_db_destroy (GtkObject *object);
+
+static GnomeVFSURI *cal_backend_db_get_uri (CalBackend *backend);
+static void cal_backend_db_add_cal (CalBackend *backend, Cal *cal);
+static CalBackendOpenStatus cal_backend_db_open (CalBackend *backend,
+                                                 GnomeVFSURI *uri,
+                                                 gboolean only_if_exists);
+
+static int cal_backend_db_get_n_objects (CalBackend *backend, CalObjType type);
+static char *cal_backend_db_get_object (CalBackend *backend, const char *uid);
+static CalObjType cal_backend_db_get_type_by_uid (CalBackend *backend, const char *uid);
+static GList* cal_backend_db_get_uids (CalBackend *backend, CalObjType type);
+static GList* cal_backend_db_get_objects_in_range (CalBackend *backend,
+                                                   CalObjType type,
+                                                   time_t start,
+                                                   time_t end);
+static GNOME_Evolution_Calendar_CalObjChangeSeq *cal_backend_db_get_changes (
+	CalBackend *backend, CalObjType type, const char *change_id);
+
+static GNOME_Evolution_Calendar_CalComponentAlarmsSeq *cal_backend_db_get_alarms_in_range (
+	CalBackend *backend, time_t start, time_t end);
+
+static GNOME_Evolution_Calendar_CalComponentAlarms *cal_backend_db_get_alarms_for_object (
+	CalBackend *backend, const char *uid, time_t start, time_t end, gboolean *object_found);
+
+static gboolean cal_backend_db_update_object (CalBackend *backend,
+                                              const char *uid,
+                                              const char *calobj);
+static gboolean cal_backend_db_remove_object (CalBackend *backend, const char *uid);
+
+static void close_cursor (CalBackendDB *cbdb, CalBackendDBCursor *cursor);
+static CalBackendDBCursor* open_cursor (CalBackendDB *cbdb, DB *db);
+static CalBackendDBCursor* find_cursor_by_db (CalBackendDB *cbdb, DB *db);
+static DBT* find_record_by_id (CalBackendDBCursor *cursor, const gchar *id);
+
+static CalBackendClass *parent_class;
+
+/**
+ * cal_backend_db_get_type:
+ * @void:
+ *
+ * Registers the #CalBackendDB class if necessary and returns the type ID
+ * associated to it.
+ *
+ * Return value: The type ID of the #CalBackendDB class.
+ */
+GtkType
+cal_backend_db_get_type (void)
+{
+	static GtkType cal_backend_db_type = 0;
+
+	if (!cal_backend_db_type) {
+		static const GtkTypeInfo cal_backend_db_info = {
+			"CalBackendDB",
+			sizeof (CalBackendDB),
+			sizeof (CalBackendDBClass),
+			(GtkClassInitFunc) cal_backend_db_class_init,
+			(GtkObjectInitFunc) cal_backend_db_init,
+			NULL,
+			NULL,
+			(GtkClassInitFunc) NULL
+		};
+
+		cal_backend_db_type = gtk_type_unique(CAL_BACKEND_TYPE, &cal_backend_db_info);
+	}
+
+	return cal_backend_db_type;
+}
+
+/* class initialization function for the DB backend */
+static void
+cal_backend_db_class_init (CalBackendDBClass *klass)
+{
+	GtkObjectClass *object_class;
+	CalBackendClass *backend_class;
+
+	object_class = (GtkObjectClass *) klass;
+	backend_class = (CalBackendClass *) klass;
+
+	parent_class = gtk_type_class(CAL_BACKEND_TYPE);
+
+	object_class->destroy = cal_backend_db_destroy;
+
+	backend_class->get_uri = cal_backend_db_get_uri;
+	backend_class->add_cal = cal_backend_db_add_cal;
+	backend_class->open = cal_backend_db_open;
+	backend_class->get_n_objects = cal_backend_db_get_n_objects;
+	backend_class->get_object = cal_backend_db_get_object;
+	backend_class->get_type_by_uid = cal_backend_db_get_type_by_uid;
+	backend_class->get_uids = cal_backend_db_get_uids;
+	backend_class->get_objects_in_range = cal_backend_db_get_objects_in_range;
+	backend_class->get_changes = cal_backend_db_get_changes;
+	backend_class->get_alarms_in_range = cal_backend_db_get_alarms_in_range;
+	backend_class->get_alarms_for_object = cal_backend_db_get_alarms_for_object;
+	backend_class->update_object = cal_backend_db_update_object;
+	backend_class->remove_object = cal_backend_db_remove_object;
+}
+
+/* object initialization function for the DB backend */
+static void
+cal_backend_db_init (CalBackendDB *cbdb)
+{
+	CalBackendDBPrivate *priv;
+
+	priv = g_new0(CalBackendDBPrivate, 1);
+	cbdb->priv = priv;
+}
+
+/* Destroy handler for the DB backend */
+static void
+cal_backend_db_destroy (GtkObject *object)
+{
+	CalBackendDB *cbdb;
+	CalBackendDBPrivate *priv;
+	GList *node;
+
+	g_return_if_fail(object != NULL);
+	g_return_if_fail(IS_CAL_BACKEND_DB(object));
+
+	cbdb = CAL_BACKEND_DB(object);
+	priv = cbdb->priv;
+
+	g_assert(cbdb->priv->clients == NULL);
+
+	/* clean up */
+	if (priv->uri) {
+		gnome_vfs_uri_unref(priv->uri);
+		priv->uri = NULL;
+	}
+
+	/* close open cursors */
+	while ((node = g_list_first(cbdb->priv->cursors))) {
+		close_cursor(cbdb, (CalBackendDBCursor *) node->data);
+	}
+
+	/* close open databases */
+	if (cbdb->priv->objects_db)
+		cbdb->priv->objects_db->close(cbdb->priv->objects_db, 0);
+	if (cbdb->priv->history_db)
+		cbdb->priv->history_db->close(cbdb->priv->history_db, 0);
+
+	g_free((gpointer) priv);
+	cbdb->priv = NULL;
+
+	if (GTK_OBJECT_CLASS(parent_class)->destroy)
+		(*GTK_OBJECT_CLASS(parent_class)->destroy)(object);
+}
+
+/*
+ * Private functions
+ */
+
+/* close an open cursor and frees all associated memory */
+static void
+close_cursor (CalBackendDB *cbdb, CalBackendDBCursor *cursor)
+{
+	GList *node;
+	DBT *dbt;
+
+	g_return_if_fail(cursor != NULL);
+
+	/* free all keys and data */
+	while ((node = g_list_first(cursor->keys))) {
+		dbt = (DBT *) node->data;
+		cursor->keys = g_list_remove(cursor->keys, (gpointer) dbt);
+		g_free((gpointer) dbt);
+	}
+	while ((node = g_list_first(cursor->data))) {
+		dbt = (DBT *) node->data;
+		cursor->data = g_list_remove(cursor->data, (gpointer) dbt);
+		g_free((gpointer) dbt);
+	}
+
+	/* finally, close the cursor */
+	cursor->dbc->c_close(cursor->dbc);
+
+	cbdb->priv->cursors = g_list_remove(cbdb->priv->cursors, (gpointer) cursor);
+	g_free((gpointer) cursor);
+}
+
+/* open a cursor for the given database */
+static CalBackendDBCursor *
+open_cursor (CalBackendDB *cbdb, DB *db)
+{
+	CalBackendDBCursor *cursor;
+	gint ret;
+
+	g_return_val_if_fail(IS_CAL_BACKEND_DB(cbdb), NULL);
+	g_return_val_if_fail(db != NULL, NULL);
+
+	/* search for the cursor in our list of cursors */
+	cursor = find_cursor_by_db(cbdb, db);
+	if (cursor)
+		return cursor;
+
+	/* create the cursor */
+	cursor = g_new0(CalBackendDBCursor, 1);
+	cursor->parent_db = db;
+
+	ret = db->cursor(db, NULL, &cursor->dbc, 0);
+	if (ret == 0) {
+		DBT key;
+		DBT data;
+
+		/* read data */
+		while ((ret = cursor->dbc->c_get(cursor->dbc, &key, &data, DB_NEXT)) == 0) {
+			cursor->keys = g_list_append(cursor->keys, g_memdup(&key, sizeof(key)));
+			cursor->data = g_list_append(cursor->data, g_memdup(&data, sizeof(data)));
+		}
+		if (ret == DB_NOTFOUND) {
+			cbdb->priv->cursors = g_list_prepend(cbdb->priv->cursors,
+							     (gpointer) cursor);
+			return cursor;
+		}
+
+		/* close cursor on error */
+		close_cursor(cbdb, cursor);
+	}
+
+	return NULL;
+}
+
+/* search for a cursor in the given backend */
+static CalBackendDBCursor *
+find_cursor_by_db (CalBackendDB *cbdb, DB *db)
+{
+	GList *node;
+
+	g_return_val_if_fail(IS_CAL_BACKEND_DB(cbdb), NULL);
+	g_return_val_if_fail(cbdb->priv != NULL, NULL);
+	g_return_val_if_fail(db != NULL, NULL);
+
+	for (node = g_list_first(cbdb->priv->cursors); node != NULL; node = g_list_next(node)) {
+		CalBackendDBCursor* cursor = (CalBackendDBCursor *) node->data;
+		if (cursor && cursor->parent_db == db)
+			return cursor;
+	}
+
+	return NULL; /* not found */
+}
+
+/* finds a record in a cursor by its ID */
+static DBT *
+find_record_by_id (CalBackendDBCursor *cursor, const gchar *id)
+{
+	GList *node;
+	gint pos = 0;
+
+	g_return_val_if_fail(cursor != NULL, NULL);
+	g_return_val_if_fail(id != NULL, NULL);
+
+	for (node = g_list_first(cursor->keys); node != NULL; node = g_list_next(node)) {
+		DBT* key = (DBT *) node->data;
+		if (key) {
+			if (!strcmp(key->data, id)) {
+				GList* tmp = g_list_nth(cursor->data, pos);
+				if (tmp)
+					return (DBT *) node->data;
+			}
+		}
+		pos++;
+	}
+
+	return NULL; /* not found */
+}
+
+/*
+ * Calendar backend methods
+ */
+
+/* get_uri handler for the DB backend */
+static GnomeVFSURI *
+cal_backend_db_get_uri (CalBackend *backend)
+{
+	CalBackendDB *cbdb;
+
+	cbdb = CAL_BACKEND_DB(backend);
+	g_return_val_if_fail(IS_CAL_BACKEND_DB(cbdb), NULL);
+	g_return_val_if_fail(cbdb->priv != NULL, NULL);
+
+	return cbdb->priv->uri;
+}
+
+/* callback used when a Cal is destroyed */
+static void
+destroy_cal_cb (GtkObject *object, gpointer data)
+{
+	Cal *cal;
+	Cal *tmp_cal;
+	CalBackendDB *cbdb;
+	GList *node;
+
+	cal = CAL(object);
+	cbdb = CAL_BACKEND_DB(data);
+	
+	g_return_if_fail(IS_CAL_BACKEND_DB(cbdb));
+	g_return_if_fail(cbdb->priv != NULL);
+
+	/* find the Cal in the list of clients */
+	for (node = cbdb->priv->clients; node != NULL; node = g_list_next(node)) {
+		tmp_cal = CAL(node->data);
+		if (tmp_cal == cal)
+			break;
+	}
+
+	if (node) {
+		/* disconnect this Cal */
+		cbdb->priv->clients = g_list_remove_link(cbdb->priv->clients, node);
+		g_list_free_1(node);
+
+		/* when all clients go away, notify the parent factory about it so that
+		 * it may decide to kill the backend or not.
+		 */
+		if (!cbdb->priv->clients)
+			cal_backend_last_client_gone(CAL_BACKEND(cbdb));
+	}
+}
+
+/* add_cal_handler for the DB backend */
+static void
+cal_backend_db_add_cal (CalBackend *backend, Cal *cal)
+{
+	CalBackendDB *cbdb;
+
+	cbdb = CAL_BACKEND_DB(backend);
+	g_return_if_fail(IS_CAL_BACKEND_DB(cbdb));
+	g_return_if_fail(cbdb->priv != NULL);
+	g_return_if_fail(IS_CAL(cal));
+
+	/* we do not keep a reference to the Cal since the calendar user agent
+	 * owns it
+	 */
+	gtk_signal_connect(GTK_OBJECT(cal),
+	                   "destroy",
+	                   GTK_SIGNAL_FUNC(destroy_cal_cb),
+	                   backend);
+
+	cbdb->priv->clients = g_list_prepend(cbdb->priv->clients, (gpointer) cal);
+}
+
+/* database file initialization */
+static gboolean
+open_database_file (CalBackendDB *cbdb, const gchar *str_uri, gboolean only_if_exists)
+{
+	gint ret;
+
+	g_return_val_if_fail(IS_CAL_BACKEND_DB(cbdb), FALSE);
+	g_return_val_if_fail(cbdb->priv != NULL, FALSE);
+	g_return_val_if_fail(cbdb->priv->objects_db != NULL, FALSE);
+	g_return_val_if_fail(cbdb->priv->history_db != NULL, FALSE);
+	g_return_val_if_fail(str_uri != NULL, FALSE);
+
+	/* open/create objects database into given file */
+	if (only_if_exists) {
+		ret = cbdb->priv->objects_db->open(cbdb->priv->objects_db,
+		                                   str_uri,
+		                                   "calendar_objects",
+		                                   DB_HASH,
+		                                   0,
+		                                   0644);
+	}
+	else {
+		ret = cbdb->priv->objects_db->open(cbdb->priv->objects_db,
+		                                   str_uri,
+		                                   "calendar_objects",
+		                                   DB_HASH,
+		                                   DB_CREATE,
+		                                   0644);
+	}
+	if (ret == 0) {
+		/* now, open the history database */
+		ret = cbdb->priv->history_db->open(cbdb->priv->history_db,
+		                                   str_uri,
+		                                   "calendar_history",
+		                                   DB_BTREE,
+		                                   DB_CREATE,
+		                                   0644);
+		if (ret == 0) return TRUE;
+
+		/* close objects database on error */
+		cbdb->priv->objects_db->close(cbdb->priv->objects_db, 0);
+	}
+
+	return FALSE;
+}
+
+/* open handler for the DB backend */
+static CalBackendOpenStatus
+cal_backend_db_open (CalBackend *backend, GnomeVFSURI *uri, gboolean only_if_exists)
+{
+	CalBackendDB *cbdb;
+	gchar *str_uri;
+	gint ret;
+
+	cbdb = CAL_BACKEND_DB(backend);
+	g_return_val_if_fail(IS_CAL_BACKEND_DB(cbdb), CAL_BACKEND_OPEN_ERROR);
+	g_return_val_if_fail(cbdb->priv != NULL, CAL_BACKEND_OPEN_ERROR);
+	g_return_val_if_fail(uri != NULL, CAL_BACKEND_OPEN_ERROR);
+	g_return_val_if_fail(cbdb->priv->objects_db == NULL, CAL_BACKEND_OPEN_ERROR);
+
+	/* open the given URI */
+	if (!gnome_vfs_uri_is_local(uri))
+		return CAL_BACKEND_OPEN_ERROR;
+	str_uri = gnome_vfs_uri_to_string(uri,
+					  (GNOME_VFS_URI_HIDE_USER_NAME
+					   | GNOME_VFS_URI_HIDE_PASSWORD
+					   | GNOME_VFS_URI_HIDE_HOST_NAME
+					   | GNOME_VFS_URI_HIDE_HOST_PORT
+					   | GNOME_VFS_URI_HIDE_TOPLEVEL_METHOD));
+
+	/* open database file */
+	if ((ret = db_create(&cbdb->priv->objects_db, NULL, 0)) != 0
+	    || (ret = db_create(&cbdb->priv->history_db, NULL, 0)) != 0) {
+		g_free((gpointer) str_uri);
+		return CAL_BACKEND_OPEN_ERROR;
+	}
+	if (!open_database_file(cbdb, (const gchar *) str_uri, only_if_exists)) {
+		g_free((gpointer) str_uri);
+		return CAL_BACKEND_OPEN_ERROR;
+	}
+
+	gnome_vfs_uri_ref(uri);
+	cbdb->priv->uri = uri;
+	g_free((gpointer) str_uri);
+
+	return CAL_BACKEND_OPEN_SUCCESS;
+}
+
+/* get_n_objects handler for the DB backend */
+static int
+cal_backend_db_get_n_objects (CalBackend *backend, CalObjType type)
+{
+	CalBackendDB *cbdb;
+	CalBackendDBCursor *cursor;
+	int total_count = 0;
+
+	cbdb = CAL_BACKEND_DB(backend);
+	g_return_val_if_fail(IS_CAL_BACKEND_DB(cbdb), -1);
+	g_return_val_if_fail(cbdb->priv != NULL, -1);
+
+	/* open the cursor */
+	cursor = open_cursor(cbdb, cbdb->priv->objects_db);
+	if (cursor) {
+		GList *node;
+
+		/* we traverse all data, to check for each object's type */
+		for (node = g_list_first(cursor->data); node != NULL; node = g_list_next(node)) {
+			icalcomponent *icalcomp;
+			DBT *data = (DBT *) node->data;
+
+			icalcomp = icalparser_parse_string((char *) data->data);
+			if (icalcomp) {
+				switch (icalcomponent_isa(icalcomp)) {
+				case ICAL_VEVENT_COMPONENT :
+					if (type & CALOBJ_TYPE_EVENT)
+						total_count++;
+					break;
+				case ICAL_VTODO_COMPONENTS :
+					if (type & CALOBJ_TYPE_TODO)
+						total_count++;
+					break;
+				case ICAL_VJOURNAL_COMPONENT :
+					if (type & CALOBJ_TYPE_JOURNAL)
+						total_count++;
+					break;
+				}
+				icalcomponent_free(icalcomp);
+			}
+		}
+	}
+
+	return total_count;
+}
+
+/* get_object handler for the DB backend */
+static char *
+cal_backend_db_get_object (CalBackend *backend, const char *uid)
+{
+	CalBackendDB *cbdb;
+	CalBackendDBCursor *cursor;
+
+	cbdb = CAL_BACKEND_DB(backend);
+	g_return_val_if_fail(IS_CAL_BACKEND_DB(cbdb), NULL);
+	g_return_val_if_fail(cbdb->priv != NULL, NULL);
+	g_return_val_if_fail(cbdb->priv->objects_db != NULL, NULL);
+	g_return_val_if_fail(uid != NULL, NULL);
+
+	/* open cursor */
+	cursor = open_cursor(cbdb, cbdb->priv->objects_db);
+	if (cursor) {
+		gint ret;
+		DBT *data;
+
+		data = find_record_by_id(cursor, uid);
+		if (data)
+			return (char *) data->data;
+	}
+
+	return NULL;
+}
+
+/* get_type_by_uid handler for the DB backend */
+static CalObjType
+cal_backend_db_get_type_by_uid (CalBackend *backend, const char *uid)
+{
+	CalBackendDB *cbdb;
+	CalBackendDBCursor *cursor;
+
+	cbdb = CAL_BACKEND_DB(backend);
+	g_return_val_if_fail(IS_CAL_BACKEND_DB(cbdb), CAL_COMPONENT_NO_TYPE);
+	g_return_val_if_fail(cbdb->priv != NULL, CAL_COMPONENT_NO_TYPE);
+	g_return_val_if_fail(cbdb->priv->objects_db != NULL, CAL_COMPONENT_NO_TYPE);
+	g_return_val_if_fail(uid != NULL, CAL_COMPONENT_NO_TYPE);
+
+	/* open the cursor */
+	cursor = open_cursor(cbdb, cbdb->priv->objects_db);
+	if (cursor) {
+		DBT *data = find_record_by_id(cursor, uid);
+		if (data) {
+			icalcomponent icalcomp = icalparser_parse_string((char *) data->data);
+			if (icalcomp) {
+				CalObjType type;
+
+				switch (icalcomponent_isa(icalcomp)) {
+				case ICAL_VEVENT_COMPONENT :
+					type = CALOBJ_TYPE_EVENT;
+					break;
+				case ICAL_VTODO_COMPONENT :
+					type = CALOBJ_TYPE_TODO;
+					break;
+				case ICAL_VJOURNAL_COMPONENT :
+					type = CALOBJ_TYPE_JOURNAL;
+					break;
+				default :
+					type CAL_COMPONENT_NO_TYPE;
+				}
+
+				icalcomponent_free(icalcomp);
+				return type;
+			}
+		}
+	}
+
+	return CAL_COMPONENT_NO_TYPE;
+}
+
+static GList *
+add_uid_if_match (GList *list, CalBackendDBCursor *cursor, GList *data_node, CalObjType type)
+{
+	DBT *data;
+
+	g_return_val_if_fail(cursor != NULL, list);
+	g_return_val_if_fail(data_node != NULL, list);
+	
+	data = (DBT *) data_node->data;
+	if (data) {
+		icalcomponent *icalcomp;
+		gchar *uid;
+
+		icalcomp = icalparser_parse_string(data->data);
+		if (!icalcomp) return list;
+		switch (icalcomponent_isa(icalcomp)) {
+		case ICAL_VEVENT_COMPONENT :
+			if (type & CALOBJ_TYPE_EVENT)
+				uid = icalcomponent_get_uid(icalcomp);
+			break;
+		case ICAL_VTODO_COMPONENT :
+			if (type & CALOBJ_TYPE_TODO)
+				uid = icalcomponent_get_uid(icalcomp);
+			break;
+		case ICAL_VJOURNAL_COMPONENT :
+			if (type & CALOBJ_TYPE_JOURNAL)
+				uid = icalcomponent_get_uid(icalcomp);
+			break;
+		default :
+			uid = NULL;
+		}
+
+		if (uid)
+			list = g_list_prepend(list, g_strdup(uid));
+		icalcomponent_free(icalcomp);
+	}
+
+	return list;
+}
+
+/* get_uids handler for the DB backend */
+static GList *
+cal_backend_db_get_uids (CalBackend *backend, CalObjType type)
+{
+	CalBackendDB *cbdb;
+	GList *list = NULL;
+	CalBackendDBCursor *cursor;
+
+	cbdb = CAL_BACKEND_DB(backend);
+	g_return_val_if_fail(IS_CAL_BACKEND_DB(cbdb), NULL);
+	g_return_val_if_fail(cbdb->priv != NULL, NULL);
+	g_return_val_if_fail(cbdb->priv->objects_db != NULL, NULL);
+
+	/* open cursor */
+	cursor = open_cursor(cbdb, cbdb->priv->objects_db);
+	if (cursor) {
+		GList *node;
+
+		/* we traverse all data, to check for each object's type */
+		for (node = g_list_first(cursor->data); node != NULL; node = g_list_next(node)) {
+			list = add_uid_if_match(list, cursor, node, type);
+		}
+	}
+
+	return list;
+}
+
+/* callback used from cal_recur_generate_instances(): adds the component's UID to
+ * our hash table
+ */
+static gboolean
+add_instance (CalComponent *comp, time_t start, time_t end, gpointer data)
+{
+	GHashTable *uid_hash;
+	const char *uid;
+	const char *old_uid;
+
+	uid_hash = data;
+
+	cal_component_get_uid(comp, &uid);
+
+	old_uid = g_hash_table_lookup(uid_hash, uid);
+	if (old_uid)
+		return FALSE;
+
+	g_hash_table_insert(uid_hash, (char *) uid, NULL);
+	return FALSE;
+}
+
+/* creates the list of UIDs in the given range */
+static void
+get_instances_in_range (GHashTable *uid_hash,
+                        CalBackendDBCursor *cursor,
+                        CalObjType type,
+                        time_t start,
+                        time_t end)
+{
+	GList *node;
+
+	g_return_if_fail(uid_hash != NULL);
+	g_return_if_fail(cursor != NULL);
+
+	for (node = g_list_first(cursor->data); node != NULL; node = g_list_next(node)) {
+		DBT *data;
+		icalcomponent *icalcomp;
+
+		data = (DBT *) node->data;
+		if (data) {
+			icalcomp = icalparser_parse_string((char *) data->data);
+			if (icalcomp) {
+				CalComponent *comp = cal_component_new();
+				cal_component_set_icalcomponent(comp, icalcomp);
+
+				switch (icalcomponent_isa(icalcomp)) {
+				case ICAL_VEVENT_COMPONENT :
+					if (type & CALOBJ_TYPE_EVENT)
+						cal_recur_generate_instances(comp,
+						                             start,
+						                             end,
+						                             add_instance,
+						                             uid_hash);
+					break;
+				case ICAL_VTODO_COMPONENT :
+					if (type & CALOBJ_TYPE_TODO)
+						cal_recur_generate_instances(comp,
+						                             start,
+						                             end,
+						                             add_instance,
+						                             uid_hash);
+					break;
+				case ICAL_VJOURNAL_COMPONENT :
+					if (type & CALOBJ_TYPE_JOURNAL)
+						cal_recur_generate_instances(comp,
+						                             start,
+						                             end,
+						                             add_instance,
+						                             uid_hash);
+					break;
+				}
+
+				gtk_object_unref(comp);
+				icalcomponent_free(icalcomp);
+			}
+		}
+	}
+}
+
+/* callback used from g_hash_table_foreach: adds a UID from the hash table to our list */
+static void
+add_uid_to_list (gpointer key, gpointer value, gpointer data)
+{
+	GList **list;
+	const char *uid;
+
+	list = (GList **) data;
+
+	uid = (const char *) key;
+	*list = g_list_prepend(*list, (gpointer) g_strdup(uid));
+}
+
+/* get_objects_in_range handler for the DB backend */
+static GList *
+cal_backend_db_get_objects_in_range (CalBackend *backend,
+                                     CalObjType type,
+                                     time_t start,
+                                     time_t end)
+{
+	CalBackendDB *cbdb;
+	GList *list = NULL;
+	CalBackendDBCursor *cursor;
+
+	cbdb = CAL_BACKEND_DB(backend);
+	g_return_val_if_fail(IS_CAL_BACKEND_DB(cbdb), NULL);
+	g_return_val_if_fail(cbdb->priv != NULL, NULL);
+
+	/* open cursor */
+	cursor = open_cursor(cbdb, cbdb->priv->objects_db);
+	if (cursor) {
+		GHashTable *uid_hash;
+
+		/* build the hash table */
+		uid_hash = g_hash_table_new(g_str_hash, g_str_equal);
+		get_instances_in_range(uid_hash, cursor, type, start, end);
+
+		/* build the list to be returned from the hash table */
+		g_hash_table_foreach(uid_hash, add_uid_to_list, &list);
+		g_hash_table_destroy(uid_hash);
+	}
+	
+	return list;
+}
+
+/* get_changes handler for the DB backend */
+static GNOME_Evolution_Calendar_CalObjChangeSeq *
+cal_backend_db_get_changes (CalBackend *backend, CalObjType type, const char *change_id)
+{
+	CalBackendDB *cbdb;
+
+	cbdb = CAL_BACKEND_DB(backend);
+	g_return_val_if_fail(IS_CAL_BACKEND_DB(cbdb), NULL);
+	g_return_val_if_fail(cbdb->priv != NULL, NULL);
+
+	return NULL;
+}
+
+/* get_alarms_in_range handler for the DB backend */
+static GNOME_Evolution_Calendar_CalComponentAlarmsSeq *
+cal_backend_db_get_alarms_in_range (CalBackend *backend, time_t start, time_t end)
+{
+	CalBackendDB *cbdb;
+	CalBackendDBCursor *cursor;
+	gint number_of_alarms;
+	GList *alarm_list;
+	GList *node;
+	gint i;
+	GNOME_Evolution_Calendar_CalComponentAlarmsSeq *seq = NULL;
+
+	cbdb = CAL_BACKEND_DB(backend);
+	g_return_val_if_fail(IS_CAL_BACKEND_DB(cbdb), NULL);
+	g_return_val_if_fail(cbdb->priv != NULL, NULL);
+	g_return_val_if_fail (start != -1 && end != -1, NULL);
+	g_return_val_if_fail (start <= end, NULL);
+
+	/* open cursor */
+	cursor = open_cursor(cbdb, cbdb->priv->objects_db);
+	if (cursor) {
+		/* TODO: get list of alarms */
+		
+		/* create the CORBA sequence */
+		seq = GNOME_Evolution_Calendar_CalComponentAlarmsSeq__alloc();
+		CORBA_sequence_set_release(seq, TRUE);
+		seq->_length = number_of_alarms;
+		seq->_buffer = CORBA_sequence_GNOME_Evolution_Calendar_CalComponentAlarms_allocbuf(number_of_alarms);
+		
+		/* TODO: populate CORBA sequence */
+	}
+	
+	g_list_free(alarm_list);
+
+	return seq;
+}
+
+/* get_alarms_for_object handler for the DB backend */
+static GNOME_Evolution_Calendar_CalComponentAlarms *
+cal_backend_db_get_alarms_for_object (CalBackend *backend,
+                                      const char *uid,
+                                      time_t start,
+                                      time_t end,
+                                      gboolean *object_found)
+{
+	CalBackendDB *cbdb;
+	CalBackendDBCursor *cursor;
+	GNOME_Evolution_Calendar_CalComponentAlarms *corba_alarms = NULL;
+
+	cbdb = CAL_BACKEND_DB(backend);
+	g_return_val_if_fail(IS_CAL_BACKEND_DB(cbdb), NULL);
+	g_return_val_if_fail(cbdb->priv != NULL, NULL);
+	g_return_val_if_fail(uid != NULL, NULL);
+	g_return_val_if_fail(start != -1 && end != -1, NULL);
+	g_return_val_if_fail(start <= end, NULL);
+	g_return_val_if_fail(object_found != NULL, NULL);
+
+	/* open the cursor */
+	cursor = open_cursor(cbdb, cbdb->priv->object_db);
+	if (cursor) {
+		/* TODO: retrieve list of alarms for this object */
+		
+		/* create the CORBA alarms */
+		corba_alarms = GNOME_Evolution_Calendar_CalComponentAlarms__alloc();
+		
+		/* TODO: populate the CORBA alarms */
+	}
+
+	return corba_alarms;
+}
+
+/* update_object handler for the DB backend */
+static gboolean
+cal_backend_db_update_object (CalBackend *backend, const char *uid, const char *calobj)
+{
+	CalBackendDB *cbdb;
+	CalBackendDBCursor *cursor;
+
+	cbdb = CAL_BACKEND_DB(backend);
+	g_return_val_if_fail(IS_CAL_BACKEND_DB(cbdb), FALSE);
+	g_return_val_if_fail(cbdb->priv != NULL, FALSE);
+	g_return_val_if_fail(uid != NULL, FALSE);
+	g_return_val_if_fail(calobj != NULL, FALSE);
+
+	/* open the cursor */
+	cursor = open_cursor(cbdb, cbdb->priv->objects_db);
+	if (cursor) {
+		DBT *data;
+		
+		data = find_record_by_id(cursor, uid);
+		if (data) {
+			DBT key;
+			DBT new_data;
+			int ret;
+			
+			/* try to change the value in the cursor */
+			memset(&key, 0, sizeof(key));
+			key.data = (void *) uid;
+			key.size = strlen(uid); // + 1
+			
+			memset(&new_data, 0, sizeof(new_data));
+			new_data.data = (void *) calobj;
+			new_data.size = strlen(calobj); // + 1
+			
+			/* move the cursor to the given key */
+			if ((ret = cursor->dbc->c_get(cursor->dbc, &key, NULL, DB_FIRST)) != 0) {
+				return FALSE;
+			}
+			
+			/* TODO: start transaction */
+			
+			if ((ret = cursor->dbc->c_put(cursor->dbc, &key, &new_data, DB_CURRENT)) != 0) {
+				/* TODO: rollback transaction */
+				return FALSE;
+			}
+			
+			/* TODO: update history database */
+			/* TODO: commit transaction */
+			
+			memcpy(data, &new_data, sizeof(new_data));
+			
+			return TRUE;
+		}
+	}
+	
+	return FALSE;
+}
+
+/* remove_object handler for the DB backend */
+static gboolean
+cal_backend_db_remove_object (CalBackend *backend, const char *uid)
+{
+	CalBackendDB *cbdb;
+	CalBackendDBCursor *cursor;
+
+	cbdb = CAL_BACKEND_DB(backend);
+	g_return_val_if_fail(IS_CAL_BACKEND_DB(cbdb), FALSE);
+	g_return_val_if_fail(cbdb->priv != NULL, FALSE);
+	g_return_val_if_fail(uid != NULL, FALSE);
+	
+	/* open cursor */
+	cursor = open_cursor(cbdb, cbdb->priv->objects_db);
+	if (cursor) {
+		DBT *data = find_record_by_id(cursor, uid);
+		if (data) {
+			GList *l;
+			int ret;
+			DBT key;
+			
+			memset(&key, 0, sizeof(key);
+			key.data = (void *) uid;
+			key.size = strlen(uid); // + 1
+			
+			if ((ret = cursor->dbc->c_get(cursor->dbc, &key, NULL, DB_FIRST)) != 0) {
+				return FALSE;
+			}
+			
+			/* TODO: begin transaction */
+			
+			/* remove record from cursor */
+			if ((ret = cursor->dbc->c_del(cursor->dbc, 0)) != 0) {
+				/* TODO: rollback transaction */
+				return FALSE;
+			}
+			
+			/* TODO: update history database */
+			/* TODO: commit transaction */
+			
+			/* remove record from in-memory lists */
+			l = g_list_nth(cursor->keys,
+			               g_list_index(cursor->data, (gpointer) data));
+			if (l) {
+				DBT *key_to_free = (DBT *) l->data;
+				
+				cursor->keys = g_list_remove(cursor->keys, (gpointer) key_to_free);
+				g_free((gpointer) key_to_free);
+				
+				cursor->data = g_list_remove(cursor->data, (gpointer) data);
+				g_free((gpointer) data);
+			}
+			
+			return TRUE;
+		}
+	}
+	
+	return FALSE;
+}