MongoDB的C驱动mongoc_collection_find（）无法通过现场找到文件 [英] MongoDB C driver mongoc_collection_find() can't find Document by field

问题描述

我试图找到这里面的对象字段名的文件。
我有集合名称这里面的1号文件为TestCollection

  {
    _id：的ObjectId（56c2f0f3892b312e740041a1），
    的Obj：{
        类型：0，
        民：NumberLong（1111111111111）
    }
}
 

根据这个教程： http://api.mongodb.org/c /current/tutorial.html#find 结果
而关于这个API文档中找到我知道我需要使用点符号由Obj.Num搜索
我试图找到这个文件是这样的：

  mongoc_collection_t *收集= NULL;
mongoc_cursor_t *光标= NULL;
常量bson_t *文档= NULL;
字符*海峡= NULL;
bson_t *查询= bson_new（）;
性病::字符串str;
布尔B = BSON_APPEND_INT64（查询，TestCollection.Num1111111111111）;
// b为真
集合= mongoc_client_get_collection（m_mogoClientCollectionDB，Obj.Num）;
光标= mongoc_collection_find（收集，MONGOC_QUERY_NONE，0，0，0，查询，NULL，NULL）;
 而（mongoc_cursor_next（光标，＆安培; DOC））{
             //这是从来没有在这里得到打印的文档
             海峡= bson_as_json（DOC，NULL）;
             的printf（％S \\ n，STR）;
             bson_free（STR）;
}bson_destroy（查询）;
mongoc_cursor_destroy（光标）;
mongoc_collection_destroy（集合）;
 

测试查询我在MongoDB的shell中运行它
而且我也当你看到找回文档的结果：

 ＆GT;使用CollectionDB
切换到DB CollectionDB
＆GT;分贝
采集
＆GT; db.TestCollection.find（
... {
......Obj.Num：1111111111111
...}
...）
{_id：的ObjectId（56c2f0f3892b312e740041a1），的Obj：{类型0，货号：NumberLong（1111111111111）}}＆GT;
 

什么是错在c code，为什么不给我回的结果？
谢谢

解决方案

 布尔B = BSON_APPEND_INT64（查询，Obj.Num1111111111111）;
集合= mongoc_client_get_collection（m_mogoClientCollectionDB，为TestCollection）;
光标= mongoc_collection_find（收集，MONGOC_QUERY_NONE，0，0，0，查询，NULL，NULL）;
 

希望你现在想通了。

在BSON B中的点号（一号线）需要的字段命名

集合名（线路2及在你的shell code引用）是集合名称命名空间的混搭。它应该包含数据库的名称，只有集合名称。

i try to find document by field name which is inside object . i have this 1 document inside collection names "TestCollection"

{
    "_id" : ObjectId("56c2f0f3892b312e740041a1"),
    "Obj" : {
        "Type" : 0,
        "Num" : NumberLong(1111111111111)
    }
}

Based on this tutorial : http://api.mongodb.org/c/current/tutorial.html#find
And this API doc about "find" i learn that i need to use dot notation to search by Obj.Num I try to find this document like this :

mongoc_collection_t *collection  = NULL;
mongoc_cursor_t *cursor  = NULL;
const bson_t *doc  = NULL;
char *str = NULL;
bson_t * query = bson_new ();
std::string str;
bool b = BSON_APPEND_INT64(query,"TestCollection.Num",1111111111111);
// b is true
collection = mongoc_client_get_collection(m_mogoClient,"CollectionDB","Obj.Num");
cursor = mongoc_collection_find (collection, MONGOC_QUERY_NONE, 0, 0, 0, query, NULL, NULL);




 while (mongoc_cursor_next (cursor, &doc)) {
             //it is never gets here to print the document 
             str = bson_as_json (doc, NULL);
             printf ("%s\n", str);
             bson_free (str);
}

bson_destroy (query);
mongoc_cursor_destroy (cursor);
mongoc_collection_destroy (collection);

to test the query i run it in the mongoDB shell and i did get back the document result as you see :

> use CollectionDB
switched to db CollectionDB
> db
Collection
> db.TestCollection.find(
... {
... "Obj.Num":1111111111111
... }
... )
{ "_id" : ObjectId("56c2f0f3892b312e740041a1"), "Obj" : { "Type" : 0, "Num" : NumberLong("1111111111111") } }

>

what is wrong in the c code , why it is not giving me back result ? thanks

解决方案

bool b = BSON_APPEND_INT64(query,"Obj.Num",1111111111111);
collection = mongoc_client_get_collection(m_mogoClient,"CollectionDB","TestCollection");
cursor = mongoc_collection_find (collection, MONGOC_QUERY_NONE, 0, 0, 0, query, NULL, NULL);

Hopefully you figured it out by now.

the dot notation in bson b (line1) needs to be the namespace of the field

the Collection name (line 2 & referenced in your shell code) was mashup of the collection name and the namespace. It should be contain the database name and the collection name only.

这篇关于MongoDB的C驱动mongoc_collection_find（）无法通过现场找到文件的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！