Undo: Track and undo or redo entity changes
[Query Object Framework]

Detailed Description

QOF Undo operates within a QofBook. In order to undo the changes to the entity, the initial state of each parameter is cached when an operation begins. If the entity changes are not successful, the lack of a qof_book_end_operation call before a qof_book_start_operation will cause the cached data to be freed. If the entity is changed successfully, qof_book_end_operation will create the undo data using the operation label and each of the entity changes that were successful.

Within each operation, entity changes can be recorded using QofEventHandler or individually.

Undo data consists of a list of operations that have changed data in this book and a list of entity changes for each of those operations. Each operation can relate to more than one entity change and cover more than one entity but must only relate to one book.

  1. Only QOF parameter changes can be undone or redone. Data from structs that are not QOF objects or which have no QofParam to get and set the data will not be available to the undo process.
  2. Undo relates to 'user interface operations', not engine events. This is because an operation (like an import or voiding a transaction) can involve multiple, possibly conflicting, engine events - e.g. removing an entity from one reference and inserting it as another. Therefore, the UI developer alone can decide where an operation begins and ends. All changes between the two will be undone or redone in one call to qof_book_undo.
  3. Undo operations cannot be nested. Be careful where you start and end an undo operation, if your application calls qof_book_start_operation() before calling qof_book_end_operation(), the undo cache will be freed and QofUndo will not notify you of this. The API is designed to silently handle user aborts during a user operation. As undo data is cached when editing begins, if the edit is never completed the cache must be cleared before the next operation. i.e. if the user starts to edit an entity but then cancels the operation, there are no changes to undo. It follows that any one book can only be the subject of one operation at a time.



file  qofundo.h
 QOF undo handling.


#define QOF_MOD_UNDO   "qof-undo"


void qof_undo_set_param (QofEntity *ent, const QofParam *param, gchar *value)
 Set a value in this parameter of the entity.
void qof_undo_modify (QofInstance *inst, const QofParam *param)
void qof_undo_commit (QofInstance *inst, const QofParam *param)
void qof_undo_create (QofInstance *inst)
void qof_undo_delete (QofInstance *inst)
void qof_book_clear_undo (QofBook *book)
 Free the entire undo list for this book.
void qof_book_undo (QofBook *book)
 Set parameter values from before the previous event.
void qof_book_redo (QofBook *book)
 Set parameter values from after the previous event.
gboolean qof_book_can_undo (QofBook *book)
 event handler for undo widget
gboolean qof_book_can_redo (QofBook *book)
 event handler for redo widget
void qof_book_start_operation (QofBook *book, gchar *label)
 Start recording operation.
void qof_book_end_operation (QofBook *book)
 End recording the current operation.
QofTimeqof_book_undo_first_modified (QofBook *book)
 HIG compliance aid to report time of first change.
gint qof_book_undo_count (QofBook *book)
 Number of undo operations available.

Function Documentation

gboolean qof_book_can_redo ( QofBook book  ) 

event handler for redo widget

FALSE if index_position == 0 or index_position == length otherwise TRUE.

Definition at line 442 of file qofundo.c.

00443 {
00444     QofUndo *book_undo;
00445     gint length;
00447     book_undo = book->undo_data;
00448     length = g_list_length (book_undo->undo_list);
00449     if ((book_undo->index_position == length) || (length == 0))
00450         return FALSE;
00451     return TRUE;
00452 }

gboolean qof_book_can_undo ( QofBook book  ) 

event handler for undo widget

FALSE if length == 0 or index_position == 0, otherwise TRUE.

Definition at line 429 of file qofundo.c.

00430 {
00431     QofUndo *book_undo;
00432     gint length;
00434     book_undo = book->undo_data;
00435     length = g_list_length (book_undo->undo_list);
00436     if ((book_undo->index_position == 0) || (length == 0))
00437         return FALSE;
00438     return TRUE;
00439 }

void qof_book_clear_undo ( QofBook book  ) 

Free the entire undo list for this book.

The application needs to decide whether to reset the undo list upon session_save, application close, user intervention etc.

Definition at line 409 of file qofundo.c.

00410 {
00411     QofUndoOperation *operation;
00412     QofUndo *book_undo;
00414     if (!book)
00415         return;
00416     book_undo = book->undo_data;
00417     while (book_undo != NULL)
00418     {
00419         operation = (QofUndoOperation *) book_undo->undo_list->data;
00420         if(operation->entity_list)
00421             g_list_free (operation->entity_list);
00422         book_undo->undo_list = g_list_next (book_undo->undo_list);
00423     }
00424     book_undo->index_position = 0;
00425     g_free (book_undo->undo_label);
00426 }

void qof_undo_commit ( QofInstance *  inst,
const QofParam param 

Mark this instance parameter after modification

Prepare undo data for this instance after committal. Record the modified state of this parameter of this instance so that if this operation is undone and then redone, the modification can be recreated.

Definition at line 571 of file qofundo.c.

00572 {
00573     QofUndoEntity *undo_entity;
00574     QofUndo *book_undo;
00575     QofBook *book;
00577     if (!instance || !param)
00578         return;
00579     book = instance->book;
00580     book_undo = book->undo_data;
00581     undo_entity = qof_prepare_undo (&instance->entity, param);
00582     book_undo->undo_cache =
00583         g_list_prepend (book_undo->undo_cache, undo_entity);
00584 }

void qof_undo_create ( QofInstance *  inst  ) 

prepare undo data for a new instance.

Record the creation of a new (empty) instance so that undo can delete it (and recreate it on redo).

Can be used within a QofEventHandler in response to QOF_EVENT_CREATE.

Definition at line 486 of file qofundo.c.

00487 {
00488     QofUndoEntity *undo_entity;
00489     QofBook *book;
00490     QofUndo *book_undo;
00492     if (!instance)
00493         return;
00494     book = instance->book;
00495     book_undo = book->undo_data;
00496     undo_entity = g_new0 (QofUndoEntity, 1);
00497     // to undo a create, use a delete.
00498     undo_entity->how = UNDO_DELETE;
00499     undo_entity->guid = qof_instance_get_guid (instance);
00500     undo_entity->type = instance->entity.e_type;
00501     book_undo->undo_cache =
00502         g_list_prepend (book_undo->undo_cache, undo_entity);
00503 }

void qof_undo_delete ( QofInstance *  inst  ) 

prepare undo data for an instance to be deleted.

Prepare for the deletion of an entity by storing ALL data in all editable parameters so that this delete operation can be undone.

Can be used within a QofEventHandler in response to QOF_EVENT_DESTROY, before the instance itself is deleted.

Definition at line 523 of file qofundo.c.

00524 {
00525     QofUndoEntity *undo_entity;
00526     QofIdType type;
00527     QofUndo *book_undo;
00528     QofBook *book;
00530     if (!instance)
00531         return;
00532     book = instance->book;
00533     book_undo = book->undo_data;
00534     // now need to store each parameter in a second entity, MODIFY.
00535     type = instance->entity.e_type;
00536     qof_class_param_foreach (type, undo_get_entity, instance);
00537     undo_entity = g_new0 (QofUndoEntity, 1);
00538     // to undo a delete, use a create.
00539     undo_entity->how = UNDO_CREATE;
00540     undo_entity->guid = qof_instance_get_guid (instance);
00541     undo_entity->type = type;
00542     book_undo->undo_cache =
00543         g_list_prepend (book_undo->undo_cache, undo_entity);
00544 }

void qof_undo_modify ( QofInstance *  inst,
const QofParam param 

Mark this instance parameter before modification.

Prepare undo data for this parameter of this instance. Record the initial state of this parameter of this instance in preparation for modification so that undo can reset the value if required.

Definition at line 547 of file qofundo.c.

00548 {
00549     QofBook *book;
00550     QofUndo *book_undo;
00551     QofUndoEntity *undo_entity;
00553     if (!instance || !param)
00554         return;
00555     book = instance->book;
00556     book_undo = book->undo_data;
00557     // handle if record is called without a commit.
00558     undo_entity = qof_prepare_undo (&instance->entity, param);
00559     book_undo->undo_cache =
00560         g_list_prepend (book_undo->undo_cache, undo_entity);
00561     // set the initial state that undo will reinstate.
00562     if (book_undo->index_position == 0)
00563     {
00564         book_undo->undo_list = g_list_prepend (book_undo->undo_list,
00565             qof_undo_new_operation (book, "initial"));
00566         book_undo->index_position++;
00567     }
00568 }

void qof_undo_set_param ( QofEntity ent,
const QofParam param,
gchar *  value 

Set a value in this parameter of the entity.

Setting an arbitrary parameter in an entity can involve repetitive string comparisons and setter function prototypes. This function accepts a QofParam (which determines the type of value) and a string representing the value. e.g. for a boolean, pass "TRUE", for a GUID pass the result of guid_to_string_buff.

Sets the undo data for this modification at the same time, calling qof_undo_modify, sets the parameter and qof_undo_commit.

ent An initialised QofEntity from an accessible QofBook.
param from qof_class_get_parameter
value A string representation of the required value - original type as specified in param->param_type.

Definition at line 207 of file qofundo.c.

00209 {
00210     qof_undo_modify ((QofInstance*)ent, param);
00211     set_param (ent, param, value);
00212     qof_undo_commit ((QofInstance*)ent, param);
00213 }

Generated on Thu Jan 31 22:50:27 2008 for QOF by  doxygen 1.5.4