Mongodb源码分析--更新记录
在之前的一篇文章中，介绍了assembleResponse函数(位于instance.cpp第224行)，它会根据op操作枚举类型来调用相应的crud操作，枚举类型定义如下：enum Operations {
opReply = 1, /* reply. responseTo is set. */
dbMsg = 1000, /* generic msg command followed by a string */
dbUpdate = 2001, /* 更新对象 */
dbInsert = 2002,
//dbGetByOID = 2003,
dbQuery = 2004,
dbGetMore = 2005,
dbDelete = 2006,
dbKillCursors = 2007
};
可以看到dbUpdate = 2001 为更新操作枚举值，下面我们看一下assembleResponse在确定是更新操作时调用的方法，如下：
//instance.cpp文件第224行
assembleResponse( Message &m, DbResponse &dbresponse, const SockAddr &client ) {
.....
try {
if ( op == dbInsert ) {//添加记录操作
receivedInsert(m, currentOp);
}
else if ( op == dbUpdate ) { //更新记录
receivedUpdate(m, currentOp);
}
else if ( op == dbDelete ) { //删除记录
receivedDelete(m, currentOp);
}
else if ( op == dbKillCursors ) { //删除Cursors（游标）对象
currentOp.ensureStarted();
logThreshold = 10;
ss advance();//将游标跳转到下一条记录
if ( nscanned % 256 == 0 && ! atomic ) {
if ( cc.get() == 0 ) {
shared_ptr< Cursor > cPtr = c;
cc.reset( new ClientCursor( QueryOption_NoCursorTimeout , cPtr , ns ) );
}
if ( ! cc->yield() ) {
cc.release();
// TODO should we assert or something?
break;
}
if ( !c->ok() ) {
break;
}
}
continue;
}
Record *r = c->_current();//游标当前所指向的记录
DiskLoc loc = c->currLoc();//游标当前所指向的记录所在地址
// TODO Maybe this is unnecessary since we have seenObjects
if ( c->getsetdup( loc ) ) {//判断当前记录是否是重复
c->advance();
continue;
}
BSONObj js(r);
BSONObj pattern = patternOrig;
if ( logop ) {//记录日志
BSONObjBuilder idPattern;
BSONElement id;
// NOTE: If the matching object lacks an id, we'll log
// with the original pattern.This isn't replay-safe.
// It might make sense to suppress the log instead
// if there's no id.
if ( js.getObjectID( id ) ) {
idPattern.append( id );
pattern = idPattern.obj();
}
else {
uassert( 10157 ,"multi-update requires all modified objects to have an _id" , ! multi );
}
}
if ( profile )
ss unindex(idx.head, idx, *changes.removed, dl);
}
catch (AssertionException&) {
ss
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