无法将元素添加到 bsoncxx 文档

Question

无法将元素添加到 bsoncxx 文档

    auto doc = bsoncxx::builder::basic::document{};

    const char* key = "asd";
    const char* value = "123";

    doc.append(kvp(key, value));

bsoncxx::v_noabi::builder::basic::sub_document::append_(bsoncxx::v_noabi::builder::concatenate_doc)': cannot convert argument 1 from '_Ty' to 'bsoncxx::v_noabi::builder::concatenate_doc'
1>          with
1>          [
1>              _Ty=std::tuple<const char *&,const char *&>
1>          ]

但此代码有效

    auto doc = bsoncxx::builder::basic::document{};

    const char* key = "asd";
    const char* value = "123";

    doc.append(kvp("asd", value));

mongo cxx 驱动 v3.3.1

Answer 1

您的初始代码不起作用，因为 sub_document::append_ 没有针对 const char* 的专门化（模板只有 enabled for std::string and string_view）。

你的第二个例子确实有效，因为有一个 for string literals.

错误跟踪的以下部分提供了更多信息：

1>    c:\mongo-cxx-driver\include\bsoncxx\v_noabi\bsoncxx\builder\basic\sub_document.hpp(46):
    note: No user-defined-conversion operator available that can perform this conversion, or the operator cannot be called
1>    c:\c++\workspace\test.cpp(207):
    note: see reference to function template instantiation 'void bsoncxx::v_noabi::builder::basic::sub_document::append<std::tuple<const char *&,const char *&>,>(Arg &&)' being compiled

要使其正常工作，您只需将其作为 std::string 传递（最好直接将密钥构建为 std::string）：

auto doc = bsoncxx::builder::basic::document{};

const char* key = "asd";                  // or: std::string keyStr("asd");
const char* value = "123";

doc.append(kvp(std::string(key), value)); // or: doc.append(kvp(keyStr,value));

如果你真的想使用 const char* 你可以在 bsoncxx/builder/basic/sub_document.hpp:

添加 append_ 的特化

template <typename K, typename V>
BSONCXX_INLINE typename std::enable_if<
    std::is_same<typename std::decay<K>::type, const char *>::value>::type
append_(std::tuple<K, V>&& t) {
        _core->key_owned(std::forward<K>(std::get<0>(t)));
        impl::value_append(_core, std::forward<V>(std::get<1>(t)));
}

希望对您有所帮助！

Answer 2

这段代码有效

#include <bsoncxx/stdx/string_view.hpp>

    auto doc = bsoncxx::builder::basic::document{};

    bsoncxx::stdx::string_view key = "asd";
    const char* value = "123";

    doc.append(kvp(key, value));

无法将元素添加到 bsoncxx 文档

Can't add element to bsoncxx document

c++

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