Simple program to create and print out two records:
main.cpp
#include <bsoncxx/builder/stream/document.hpp> #include <bsoncxx/types.hpp> #include <bsoncxx/json.hpp> #include <mongocxx/client.hpp> #include <mongocxx/instance.hpp> #include <mongocxx/uri.hpp> #include <iostream> int main() { mongocxx::instance inst{}; mongocxx::client conn{ mongocxx::uri{} }; auto db = conn["testcursor"]; db["names"].drop(); bsoncxx::document::value document = bsoncxx::builder::stream::document{} << "name" << "George" << bsoncxx::builder::stream::finalize; db["names"].insert_one(std::move(document)); document = bsoncxx::builder::stream::document{} << "name" << "Mark" << bsoncxx::builder::stream::finalize; db["names"].insert_one(std::move(document)); auto cursor = db["names"].find({}); for (auto&& doc : cursor) { std::cout << bsoncxx::to_json(doc) << std::endl; } return 0; }
Output (as expected):
{
"_id" : {
"$oid" : "57b8b1209853f297f00005c1"
},
"name" : "George"
}
{
"_id" : {
"$oid" : "57b8b1209853f297f00005c2"
},
"name" : "Mark"
}
Now, if I insert into the code cursor.begin(); right after the find():
auto cursor = db["names"].find({});
cursor.begin();
for (auto&& doc : cursor) {
std::cout << bsoncxx::to_json(doc) << std::endl;
}
Then my output is (unexpectedly missing the "George" entry):
{
"_id" : {
"$oid" : "57b8b1c99853f26e68007472"
},
"name" : "Mark"
}
My objective was to test if the cursor was empty (there is no .empty()) so I tried to use:
if ( cursor.begin() == cursor.end() ) but that seemingly advances the iterator?
- is duplicated by
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CXX-1337 Tailable cursor don't resume
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- Closed
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- is related to
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CDRIVER-1886 Expose mongoc_cursor_t 'sent' field
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- Closed
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- related to
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- Closed
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