mongodb C驱动程序查询以选择特定字段

我读到MongoDB中只能选择一个字段：

db.records.find({TimeStampSec {$lt:10} , {ch11:1})

---

例如，此查询返回所有具有TimeStampSec的对象的字段ch11。我不完全熟悉c api，但我想您应该添加第二个json obj

所以最终是这样的：

bson_init( &query );
  bson_append_start_object( &query, "TimeStampSec" );
    bson_append_int( &query, "$lt", 10 );
  bson_append_finish_object( &query );

  bson_append_start_object( &query, "$query" );
    bson_append_int( &query, "ch11", 1 );
  bson_append_finish_object( &query );
bson_finish( &query );

这对我很有用

bson query,selection;
bson_init( &query );
  bson_append_start_object( &query, "TimeStampSec" );
    bson_append_int( &query, "$lt", 10 );
  bson_append_finish_object( &query );
bson_finish( &query );

bson_init( &selection);
    bson_append_int( &selection, "ch11", 1 );
bson_finish( &selection);

    mongo_cursor *cursor=NULL;

    cursor = mongo_find( conn, "db.records",query ,selection,0,0,0);

    if(cursor!=NULL)
    {
        while( mongo_cursor_next( cursor ) == MONGO_OK )
            bson_print( &cursor->current );
    }

bson query,selection;
bson_init( &query );
  bson_append_start_object( &query, "TimeStampSec" );
    bson_append_int( &query, "$lt", 10 );
  bson_append_finish_object( &query );
bson_finish( &query );

bson_init( &selection);
    bson_append_int( &selection, "ch11", 1 );
bson_finish( &selection);

    mongo_cursor *cursor=NULL;

    cursor = mongo_find( conn, "db.records",query ,selection,0,0,0);

    if(cursor!=NULL)
    {
        while( mongo_cursor_next( cursor ) == MONGO_OK )
            bson_print( &cursor->current );
    }