Remove an element from an existing bsoncxx document

[Rustam Abdullaev]

I have a bsoncxx document that I need to clone except for its _id (ObjectId).

How can I do that?

The following does not work:

    bsoncxx::document::value clone(bsoncxx::document::view doc)
    {
      bsoncxx::builder::stream::document builder;
      for (auto& el : doc) {
        if (el.type != bsoncxx::type::k_oid) {
          builder << el.key() << el;
        }
      }
      return builder << finalize;
    }

[Andrew Morrow]

Hi -

I wouldn't use the stream builder for that, it really isn't designed for that sort of work. Try using the basic builder instead:

    bsoncxx::document::value clone(bsoncxx::document::view doc)
    {

      bsoncxx::builder::basic::document builder;

      for (auto& el : doc) {
        if (el.type != bsoncxx::type::k_oid) {

          builder.append(kvp(el.key(), el.value()));
        }
      }
      return builder.extract();
    }

You could also generalize this a bit:

    template<typename Predicate>

    bsoncxx::document::value filter(bsoncxx::document::view doc, const Predicate& predicate)
    {
      bsoncxx::builder::basic::document builder;
      for (auto& el : doc) {
        if (!predicate(el)) {
          builder.append(kvp(el.key(), el.value()));
        }
      }
      return builder.extract();
    }

Then you could call it like:

bsoncxx::document::value doc = ...

auto id_filtered = filter(doc, [](const auto& el) { return el.type == bsoncxx::type::k_oid; });

Above code is untested but should get across the idea.

Thanks,

Andrew

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[Rustam]

That doesn't work.

error C2039: 'value': is not a member of 'bsoncxx::v_noabi::document::element'

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[Andrew Morrow]

Looks like it is called get_value: https://github.com/mongodb/mongo-cxx-driver/blob/fc9a44325e03bb8bb166e814caeb23413b4ba7af/src/bsoncxx/document/element.hpp#L358

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[Andrew Morrow]

Here is a complete example:

#include <cstdlib>

#include <iostream>

#include <bsoncxx/builder/basic/document.hpp>

#include <bsoncxx/builder/basic/kvp.hpp>

#include <bsoncxx/types.hpp>

#include <bsoncxx/types/value.hpp>

#include <bsoncxx/json.hpp>

template<typename Predicate>

bsoncxx::document::value filter(bsoncxx::document::view doc, const Predicate& predicate) {

    using namespace bsoncxx::builder;

    basic::document builder;

    for (auto& el : doc) {

        if (!predicate(el)) {

            builder.append(basic::kvp(el.key(), el.get_value()));

        }

    }

    return builder.extract();

}

int main(int, char**) {

    using namespace bsoncxx::builder;

 

    auto doc_builder = basic::document{};

    doc_builder.append(basic::kvp("foo", "bar"));

    doc_builder.append(basic::kvp("baz", bsoncxx::types::b_bool{false}));

    doc_builder.append(basic::kvp("garply", bsoncxx::types::b_double{3.14159}));

    auto doc = doc_builder.extract();

    std::cout << "Original: " << bsoncxx::to_json(doc) << std::endl;

    auto doc_filtered = filter(

        doc.view(), [](const bsoncxx::document::element& el) {

            return el.key() == "foo";

    });

    std::cout << "Filtered: " << bsoncxx::to_json(doc_filtered) << std::endl;

    return EXIT_SUCCESS;

}

Running it gives:

Original: { "foo" : "bar", "baz" : false, "garply" : 3.1415899999999998826 }

Filtered: { "baz" : false, "garply" : 3.1415899999999998826 }

On Fri, Dec 15, 2017 at 3:43 PM, Rustam Abdullaev <rust...@gmail.com> wrote:

No luck:

error C2664: 'void bsoncxx::v_noabi::builder::basic::sub_document::append_(bsoncxx::v_noabi::builder::concatenate_doc)': cannot convert argument 1 from 'boost::string_view' to 'bsoncxx::v_noabi::builder::concatenate_doc'
note: No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
note: see reference to function template instantiation 'void bsoncxx::v_noabi::builder::basic::sub_document::append<boost::string_view,bsoncxx::v_noabi::types::value>(Arg &&,bsoncxx::v_noabi::types::value &&)' being compiled

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