[英]$exists query in mongodb c-api
I am trying to implement the following mongodb query in C 我正在尝试在C中实现以下mongodb查询
db.test.find({"timestamp": {"$exists":true}});
I thought it would be something like 我以为会像
bson query, existspart;
mongo_cursor cursor;
int i;
bson_init(&existspart);
bson_append_string ( &existspart, "$exists", "false" );
bson_finish(&existspart);
bson_init(&query);
bson_append_bson ( &query, "timestamp", &existspart );
bson_finish(&query);
mongo_cursor_init(&cursor, conn, "mydb.test");
mongo_cursor_set_query(&cursor, &query );
while( mongo_cursor_next( &cursor ) == MONGO_OK )
{
// blabla
}
But it does not work. 但这行不通。 What I am doing wrong? 我做错了什么?
replace 更换
bson_append_string ( &existspart, "$exists", "false" );
with 与
bson_append_bool ( &existspart, "$exists", 1 );
or 要么
bson_append_bool ( &existspart, "$exists", 0 );
if you do not want that field exist 如果您不希望该字段存在
I used a slightly different syntax: 我使用了稍微不同的语法:
bson_t* existspart = BCON_NEW("$exists", BCON_BOOL(true));
bson_t *query = bson_new();
BSON_APPEND_DOCUMENT(query, "timestamp", existspart);
mongoc_cursor_t* cursor = MongoInterface::Instance().Find("db_name", query);
const bson_t *doc;
while (mongoc_cursor_next (cursor, &doc))
{
// Do stuff...
}
bson_destroy (existspart);
bson_destroy (query);
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