长事务 (Long Transactions)

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。

 

Relationship between DeepCloneTypes and DuplicateRecordCloning for different commands and functions 

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);
}