c - mongodb c-api 中的 $exists 查询

Question

我正在尝试用 C 实现以下 mongodb 查询

db.test.find({"timestamp": {"$exists":true}});

我以为会是这样的

bson query, existspart;
mongo_cursor cursor;
int i;

bson_init(&existspart);
bson_append_string ( &existspart, "$exists", "false" );
bson_finish(&existspart);
bson_init(&query);
bson_append_bson ( &query, "timestamp", &existspart );
bson_finish(&query);    

mongo_cursor_init(&cursor, conn, "mydb.test");
mongo_cursor_set_query(&cursor, &query );
while( mongo_cursor_next( &cursor ) == MONGO_OK )
{
    // blabla
} 

但是它不起作用。我做错了什么？

Answer 1

替换

bson_append_string ( &existspart, "$exists", "false" );

与

bson_append_bool ( &existspart, "$exists", 1 );

或

bson_append_bool ( &existspart, "$exists", 0 );

如果您不希望该字段存在