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// tail.cpp
/* Copyright 2009 10gen Inc.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
/* example of using a tailable cursor */
#include "../../client/dbclient.h"
#include "../../util/goodies.h"
using namespace mongo;
void foo() { }
/* "tail" the specified namespace, outputting elements as they are added.
_id values must be inserted in increasing order for this to work. (Some other
field could also be used.)
Note: one could use a capped collection and $natural order to do something
similar, using sort({$natural:1}), and then not need to worry about
_id's being in order.
*/
void tail(DBClientBase& conn, const char *ns) {
conn.ensureIndex(ns, fromjson("{_id:1}"));
BSONElement lastId;
Query query = Query().sort("_id");
while( 1 ) {
auto_ptr<DBClientCursor> c = conn.query(ns, query, 0, 0, 0, Option_CursorTailable);
while( 1 ) {
if( !c->more() ) {
if( c->isDead() ) {
// we need to requery
break;
}
sleepsecs(1);
}
BSONObj o = c->next();
lastId = o["_id"];
cout << o.toString() << endl;
}
query = QUERY( "_id" << GT << lastId ).sort("_id");
}
}
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