mongo C驱动程序:如何使用"_id"查询文档在列表中? [英] mongo c driver: how to query documents with "_id" in a list?
问题描述
我有一个数据库，其中包含大量文档，我只想从列表中查询带有"_id"的文档.我在网上搜索了几个小时，但没有找到任何真正有效的方法，因此我在此处发布了我的问题.非常感谢您的帮助！
I have a db with huge amount of documents, and I only want to query documents with "_id" from a list. I searched online for a few hours, and did not find anything really working, so I post my question here. Thank you very much for any help!
在MongoDB命令行环境中，很容易实现我想要的.例如，查询命令如下:
in MongoDB command line environment, it is very easy to achieve what I want. The query command, for example, is as follows:
db.collection.find({"_id":{$in:[ObjectId("595320c208b0c52a8b37c151"), ObjectId("595320c208b0c52a8b37c152"), ObjectId("595320c208b0c52a8b37c153")]}})
使用mongoc驱动程序，直接通过id检索文档也很简单.下面是一个示例:
Using mongoc driver, to retrieve document by id directly is simple too. Below is an example:
bson_t *qry = bson_new();
BSON_APPEND_OID(qry, "_id", &oid);
mongoc_cursor_t *cursor = mongoc_collection_find(col, MONGOC_QUERY_NONE,
0, 0, 0, qry, NULL, NULL);
要使用"_id"以外的其他键来获取文档，同样可以轻松实现.下面是一个示例:
To fetch documents with other keys other than "_id", same thing can be achieved easily too. Below is an example:
bson_t *qry = bson_new();
qry = BCON_NEW("$query", "{", "name", "{", "$in", "[",
"Steve", "John", "Henry", "]", "}", "}");
mongoc_cursor_t *cursor = mongoc_collection_find(col, MONGOC_QUERY_NONE,
0, 0, 0, qry, NULL, NULL);
但是，当我尝试将_id放入数组时，我无法使其正常工作.我尝试了两种不同的方法.一个是:
However, when I try to put the _id's in the array, I could not get it work. I tried two different ways. One is:
bson_oid_t oid1;
bson_oid_init_from_string(&oid1, "595320c208b0c52a8b37c151");
bson_oid_t oid2;
bson_oid_init_from_string(&oid2, "595320c208b0c52a8b37c152");
bson_oid_t oid3;
bson_oid_init_from_string(&oid3, "595320c208b0c52a8b37c153");
qry = BCON_NEW("$query", "{", "_id", "{", "$in", "[",
oid1, oid2, oid3, "]", "}", "}");
mongoc_cursor_t *cursor = mongoc_collection_find(col, MONGOC_QUERY_NONE,
0, 0, 0, qry, NULL, NULL);
另一个是:
qry = BCON_NEW("$query", "{", "_id", "{", "$in", "[",
"ObjectId(\"595320c208b0c52a8b37c151\")",
"ObjectId(\"595320c208b0c52a8b37c152\")",
"ObjectId(\"595320c208b0c52a8b37c153\")", "]", "}", "}");
mongoc_cursor_t *cursor = mongoc_collection_find(col, MONGOC_QUERY_NONE,
0, 0, 0, qry, NULL, NULL);
它们都不返回任何文档.
None of them returns any document.
再次，非常感谢您提前提出任何建议，评论！
Again, thank you very much for any suggestion, comment, in advance!
我得到了我自己的原始问题的答案(请参见下面的答案).但是，如果要动态形成查询，换句话说，用例是从其他地方获取ID列表，在形成查询之前，我不知道ID是什么，我只知道它们会被传递给我的容器，例如std :: vector< std :: string> ;，如何动态形成此查询?
I got my original question answered myself (see the answer below). However, if I want to dynamically form the query, in other words, the use case is that I get the list of ids from somewhere else, before forming the query, I don't know what the ids are, I only know they will be passed to me in a container, say std::vector<std::string>, how can I form this query dynamically?
最后，我得到了解决问题的完整解决方案.
Finally, I got the complete solution to my problem.
bson_init_from_json(qry,
"{\"_id\":{\"$in\":
[{\"$oid\":\"595320c208b0c52a8b37c151\"},
{\"$oid\":\"595320c208b0c52a8b37c152\"},
{\"$oid\":\"595320c208b0c52a8b37c153\"}]}}",
-1,
NULL);
由于上述查询是由字符串构成的，因此可以动态更新，从而完全解决了我的问题！
As the above query is formed from a string, it can be updated dynamically, and thus completely solves my problem!
推荐答案
进一步调查后，我的问题得到了解答.我应该直接使用函数BCON_OID，而不是直接使用oid变量或使用字符串.以下查询有助于获取我想要的内容:
After some further investigation, I got my question answered myself. Instead of using oid variables directly or using strings, I should use the function BCON_OID. The following query helps fetch what I wanted:
qry = BCON_NEW("$query", "{", "name", "{", "$in", "[",
BCON_OID(oid1), BCON_OID(oid2), BCON_OID(oid3), "]", "}", "}");
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