C++ | bsoncxx::builder::stream | How to $push arrays in an array

[Guillaume]

Hi.

Using MongoDB C++, I would like to update existing documents in order to append subarrays to an existing array "myArrays". We assume that "myArrays" has always at least one subarray present before the update.

The structure of my documents is:

{
  "myArrays": [
      [
        1,
        2,
        3
      ]
  ]
}

Now, Lets assume that I have a 2D vector:

std::vector<std::vector<int>> arrays; // the first one contains { 4, 5, 6 } and the second one { 7, 8, 9 }

I would like to update a given document (selected by its _id) with bsoncxx::builder::stream in order to obtain this:

{
  "myArrays": [
      [
        1,
        2,
        3
      ],
      [
        4,
        5,
        6
      ],
      [
        7,
        8,
        9
      ]
  ]
}

Obviously, I need to use the collection.update() method as well as $push (and probably $each) but so far I have failed to implement this function.

Could you please help me?

Thank you!

[Isabella Siu]

Hi,

This is a example of how I implemented it:

#include <bsoncxx/builder/stream/array.hpp>

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

#include <bsoncxx/builder/stream/helpers.hpp>

#include <mongocxx/client.hpp>

#include <mongocxx/instance.hpp>

#include <mongocxx/uri.hpp>

int main() {

  mongocxx::instance inst{};

  mongocxx::client conn{mongocxx::uri{}};

  auto db = conn["test"];

  std::vector<std::vector<int>> arrays;

  std::vector<int> v1;

  v1.push_back(4);

  v1.push_back(5);

  v1.push_back(6);

  arrays.push_back(v1);

  std::vector<int> v2;

  v2.push_back(7);

  v2.push_back(8);

  v2.push_back(9);

  arrays.push_back(v2);

  using bsoncxx::builder::stream::document;

  using bsoncxx::builder::stream::array;

  using bsoncxx::builder::stream::open_array;

  using bsoncxx::builder::stream::close_array;

  using bsoncxx::builder::stream::open_document;

  using bsoncxx::builder::stream::close_document;

  auto arr = array{};

  for (int i = 0; i < arrays.size(); i++) {

    arr << open_array;

    for (int j = 0; j < arrays[i].size(); j++) {

      arr << arrays[i][j];

    }

    arr << close_array;

  }

  document filter_builder, update_builder;

  filter_builder << "_id" << 1;

  update_builder << "$push" << open_document << "myArrays" << open_document

                 << "$each" << arr.view() << close_document << close_document;

  db["array_thing"].update_one(filter_builder.view(), update_builder.view());

}

I hope it helps!

[Guillaume]

It seems to work!

Thank you very much Isabella.