Can you change a bsoncxx object (document/value/element)? - c++

Question

I'm using the mongocxx driver and I am considering keeping the query results given in BSON as a data holder in a couple of objects instead of parsing the BSON to retrieve the values and then discard it.
This would make some sense "if" I can edit the BSON on the fly. I couldn't find anything in the bsoncxx driver documentation besides the builder that would allow me to manipulate a bsoncxx document/value/view/element after it's been constructed.
As an example, imagine that I have something like this
fruit["orange"];
where fruit is a bsoncxx::document::element
I can get the value by using one of the .get_xxx operators.
What I can't find is something like
fruit["orange"] = "ripe";
Is there a way of doing this, or the idea behind the builder is "just" to create a query to give to the database?

Answer 1

There was a question with same theme, see here
So, bsoncxx objects seem to be immutable, and we have to re-create them if we need to edit them.. :(
I've written a really bad solution which re-creates document from scratch
But this is a solution, I guess.
std::string bsoncxx_string_viewToString(core::v1::string_view gotStringView) {
std::stringstream convertingStream;
convertingStream << gotStringView;
return std::move(convertingStream.str());
}
std::string b_utf8ToString(bsoncxx::types::b_utf8 gotB_utf8) {
return std::move(bsoncxx_string_viewToString(core::v1::string_view(gotB_utf8)));
}
template <typename T>
bsoncxx::document::value editBsoncxx(bsoncxx::document::view documentToEdit, std::string keyToEdit, T newValue, bool appendValueIfKeyNotExist = true) {
auto doc = bsoncxx::builder::stream::document{};
std::string currentKey;
for (auto i : documentToEdit) {
currentKey = bsoncxx_string_viewToString(i.key());
if (currentKey == keyToEdit) {
doc << keyToEdit << newValue;
appendValueIfKeyNotExist = false;
} else {
doc << currentKey << i.get_value();
}
}
if (appendValueIfKeyNotExist) // Maybe this would be better with documentToEdit.find(key), but I don't know how to check if iterator is past-the-end
//If there is a way to check if bsoncxx contains key, we can achieve ~o(log(n)) [depending on 'find key' implementation] which is better than o(n)
doc << keyToEdit << newValue;
return doc.extract();
}
Usage:
auto doc = document{} << "foo0" << "bar0" << "foo1" << 1 << "foo2" << 314 << finalize;
std::cout << bsoncxx::to_json(doc) << std::endl << std::endl;
doc = editBsoncxx<std::string> (doc.view(), "foo1", "edited"); //replace "foo1" with string "edited"
doc = editBsoncxx<int>(doc.view(), "baz_noappend", 123, false); //do nothing if key "baz_noappend" is not found. <- if key-existance algorythm will be applied, we'd spend about o(lob(n)) here, not o(n)
doc = editBsoncxx<int>(doc.view(), "baz_append", 123, true); //key will not be found => it'll be appended which is default behaviour
std::cout << bsoncxx::to_json(doc) << std::endl;
Result:
{
"foo0" : "bar0",
"foo1" : 1,
"foo2" : 314
}
{
"foo0" : "bar0",
"foo1" : "edited",
"foo2" : 314,
"baz_append" : 123
}
So, in your case you can use
fruit = editBsoncxx<std::string>(fruit.view(), "orange", "ripe");
But, again, see already-mentioned related question you're right when saying that
the idea behind the builder is "just" to create a query to give to the database?
I think, the solution will be "do not edit documents".
also you can write something like type-converter from bsoncxx to other json storing fomat (for example, rapidjson)
Beware of {value:"valid_json"}: bsoncxx::to_json does not add backslashes to quote signs in values => injection can be made.