Method readImpl

src/DataStreams/MongoDBBlockInputStream.cpp:310–366

Block MongoDBBlockInputStream::readImpl()
{
    if (all_read)
        return {};

    MutableColumns columns(description.sample_block.columns());
    const size_t size = columns.size();

    for (const auto i : collections::range(0, size))
        columns[i] = description.sample_block.getByPosition(i).column->cloneEmpty();

    size_t num_rows = 0;
    while (num_rows < max_block_size)
    {
        Poco::MongoDB::ResponseMessage & response = cursor->next(*connection);

        for (auto & document : response.documents())
        {
            ++num_rows;

            for (const auto idx : collections::range(0, size))
            {
                const auto & name = description.sample_block.getByPosition(idx).name;

                if (strict_check_names && !document->exists(name))
                    throw Exception(fmt::format("Column {} is absent in MongoDB collection", backQuote(name)), ErrorCodes::NOT_FOUND_COLUMN_IN_BLOCK);

                const Poco::MongoDB::Element::Ptr value = document->get(name);

                if (value.isNull() || value->type() == Poco::MongoDB::ElementTraits<Poco::MongoDB::NullValue>::TypeId)
                    insertDefaultValue(*columns[idx], *description.sample_block.getByPosition(idx).column);
                else
                {
                    if (description.types[idx].second)
                    {
                        ColumnNullable & column_nullable = assert_cast<ColumnNullable &>(*columns[idx]);
                        insertValue(column_nullable.getNestedColumn(), description.types[idx].first, *value, name);
                        column_nullable.getNullMapData().emplace_back(0);
                    }
                    else
                        insertValue(*columns[idx], description.types[idx].first, *value, name);
                }
            }
        }

        if (response.cursorID() == 0)
        {
            all_read = true;
            break;
        }
    }

    if (num_rows == 0)
        return {};

    return description.sample_block.cloneWithColumns(std::move(columns));
}