长事务
长事务用于支持 AutoCAD 参照编辑功能，对于 ObjectARX 应用程序非常有用。这些类和函数为应用程序提供了一种方案，用于签出实体以进行编辑并将其签回其原始位置。此操作会将原始对象替换为已编辑的对象。有三种类型的长期交易结帐：
- 从同一图形中的普通块
- 从图形的外部参照 （外部参照）
- 从不相关的临时数据库
长事务类和函数概述
主要的长事务类和函数是
- AcDbLongTransaction.class
- AcDbLongTransWorkSetIterator.class
- AcApLongTransactionReactor.class
- AcApLongTransactionManager.class
- wblockCloneObject.class
AcDbLongTransaction Class
AcDbLongTransaction是包含跟踪长事务所需信息的类。该类AcDbLongTransactionManager负责创建AcDbLongTransaction对象并将其追加到数据库。然后它返回对象AcDbLongTransaction的AcDbObjectId。与所有其他驻留在数据库的对象一样，其销毁由数据库处理。
注意：AcDbLongTransaction对象在处于活动状态时添加到数据库中，并在事务完成后擦除。它们不存储在 DWG 或 DXF 文件中，因此不是持久性的。
AcDbLongTransWorkSetIterator Class
AcDbLongTransWorkSetIterator提供对工作集中对象的只读访问权限。在构造AcDbLongTransaction::newWorkSetIterator()期间，可以将其设置为仅包含活动工作集，或者包括添加到工作集的对象，因为它们被工作集中的对象（辅助对象）引用。它还可以处理从工作集中移除的对象，无论是通过擦除AcDbLongTransaction::removeFromWorkSet()还是被擦除。
AcApLongTransactionReactor Class
AcApLongTransactionReactor提供特定于长事务操作的通知。它旨在与也将发送的深层克隆通知结合使用，但会因正在执行的签出/签入类型而异。要将这些通知与深层克隆通知连接起来，可以通过调用AcDbLongTransaction::activeIdMap()函数来检索用于克隆的对象AcDbIdMapping。
AcApLongTransactionManager Class
AcApLongTransactionManager是用于启动和控制多头事务的管理器。每个 AutoCAD 会话只有一个acapLongTransactionManager，可通过对象返回的指针进行访问。
AcDbDatabase：：wblockCloneObjects（） Function
wblockCloneObjects()函数是AcDbDatase的成员。它将对象从一个数据库深度克隆到另一个数据库，并遵循硬引用，以便所有依赖对象也被克隆。当发现重复项时，符号表记录的行为由类型参数确定。下图显示了符号表类型 （enum DuplicateRecordCloning） 和深层克隆类型 （enum DeepCloneType） 之间的关系。
Command or API Function | DeepCloneType | DuplicateRecordCloning |
命令或 API 函数 | 深度克隆类型 | 复制记录克隆 |
copy | kDcCopy | kDrcNotApplicable |
explode | kDcExplode | kDrcNotApplicable |
block | kDcBlock | kDrcNotApplicable |
INSERT/BIND | kDcXrefInsert | kDrcIgnore |
XRESOLVE | kDcSymTableMerge | kDrcXrefMangleName |
INSERT | kDcInsert | kDrcIgnore |
insert() | kDcInsertCopy | kDrcIgnore |
WBLOCK | kDcWblock | kDrcNotApplicable |
deepCloneObjects（） | kDcObjects | kDrcNotApplicable |
wblockObjects（） | kDcObjects | kDrcIgnore |
wblockObjects（） | kDcObjects | kDrcReplace |
wblockObjects（） | kDcObjects | kDrcMangleName |
wblockObjects（） | kDcObjects | kDrcUnmangleName |
长事务示例
这个简单的示例演示如何从另一个数据库中签出实体，在当前数据库中修改它们，然后将其签回原始数据库。作为长事务过程一部分的调用以粗体显示。
void
refEditApiExample()
{
AcDbObjectId transId;
AcDbDatabase* pDb;
TCHAR *fname;
struct resbuf *rb;
// Get a dwg file from the user.
//
rb = acutNewRb(RTSTR);
int stat = acedGetFileD(_T("Pick a drawing"), NULL, _T("dwg"),
0, rb);
if ((stat != RTNORM) || (rb == NULL)) {
acutPrintf(_T("\nYou must pick a drawing file.")); return; }
fname = (TCHAR*)acad_malloc((_tcslen(rb->resval.rstring) + 1) *
sizeof(TCHAR));
_tcscpy(fname, rb->resval.rstring);
acutRelRb(rb);
// Open the dwg file.
//
pDb = new AcDbDatabase(Adesk::kFalse);
if (pDb->readDwgFile(fname) != Acad::eOk) {
acutPrintf(_T("\nSorry, that drawing is probably already
open."));
return;
}
// Get the Block Table and then the model space record.
//
AcDbBlockTable *pBlockTable;
pDb->getSymbolTable(pBlockTable, AcDb::kForRead);
AcDbBlockTableRecord *pOtherMsBtr;
pBlockTable->getAt(ACDB_MODEL_SPACE, pOtherMsBtr,
AcDb::kForRead);
pBlockTable->close();
// Create an iterator.
//
AcDbBlockTableRecordIterator *pIter;
pOtherMsBtr->newIterator(pIter);
// Set up an object ID array.
//
AcDbObjectIdArray objIdArray;
// Iterate over the model space BTR. Look specifically
// for lines and append their object ID to the array.
//
for (pIter->start(); !pIter->done(); pIter->step()) {
AcDbEntity *pEntity;
pIter->getEntity(pEntity, AcDb::kForRead);
// Look for only AcDbLine objects and add them to the
// object ID array.
//
if (pEntity->isKindOf(AcDbLine::desc())) {
objIdArray.append(pEntity->objectId());
}
pEntity->close();
}
delete pIter;
pOtherMsBtr->close();
if (objIdArray.isEmpty()) {
acad_free(fname);
acutPrintf(_T("\nYou must pick a drawing file that contains
lines."));
return;
}
// Now get the current database and the object ID for the
// current database's model space BTR.
//
AcDbBlockTable *pThisBlockTable;
acdbHostApplicationServices()->workingDatabase()->
getSymbolTable(pThisBlockTable, AcDb::kForRead);
AcDbBlockTableRecord *pThisMsBtr;
pThisBlockTable->getAt(ACDB_MODEL_SPACE, pThisMsBtr,
AcDb::kForWrite);
pThisBlockTable->close();
AcDbObjectId id = pThisMsBtr->objectId();
pThisMsBtr->close();
// Create the long transaction. This will check all the entities
// out of the external database.
//
AcDbIdMapping errorMap;
acapLongTransactionManagerPtr()->checkOut(transId, objIdArray,
id, errorMap);
// Now modify the color of these entities.
//
int colorIndex;
acedGetInt(_T("\nEnter color number to change entities to: "),
&colorIndex);
AcDbObject* pObj;
if (acdbOpenObject(pObj, transId, AcDb::kForRead) == Acad::eOk) {
// Get a pointer to the transaction.
//
AcDbLongTransaction* pLongTrans =
AcDbLongTransaction::cast(pObj);
if (pLongTrans != NULL) {
// Get a work set iterator.
//
AcDbLongTransWorkSetIterator* pWorkSetIter;
pLongTrans->newWorkSetIterator(pWorkSetIter);
// Iterate over the entities in the work set and change
// the color.
for (pWorkSetIter->start(); !pWorkSetIter->done();
pWorkSetIter->step()) {
AcDbEntity *pEntity;
acdbOpenAcDbEntity(pEntity, pWorkSetIter->objectId(),
AcDb::kForWrite);
pEntity->setColorIndex(colorIndex);
pEntity->close();
}
delete pWorkSetIter;
}
pObj->close();
}
// Pause to see the change.
//
TCHAR str[132];
acedGetString(0, _T("\nSee the new colors. Press return to check
the object into the original database"), str);
// Check the entities back in to the original database.
//
acapLongTransactionManagerPtr()->checkIn(transId, errorMap);
// Save the original database, since we have made changes.
//
pDb->saveAs(fname);
// Close/Delete the database
//
delete pDb;
pDb = NULL;
acad_free(fname);
}
