Merging json objects

[Batlan]

Hi,
I want to merge two json objects and need to ensure that the existing object is updated if a corresponding key exists in the second object.
Looking through the documentation, I found exactly what I was looking for, namely the update(j) method.

Unfortunately when using it, I realised that it doesn't fulfill my expectations. This is due to the fact that the update(j) method replaces the entire key if it is found in the update structure, instead of iterating over it in case this key contains a json subtree.

Example:

 json o1 = R"( {"one": "an element", "two": {"name": "an object", "type": "object", "aka": "glipglop"}, "three": 3})"_json;
 json o2 = R"( {"one": "an elephant", "two": {"name": "Fred", "type": "fred"}, "four": 4})"_json;
 o1.update(o2);
std::cout << o1 << '\n';

results in

{“one”: “an elephant”, “two”: {“name”: “Fred”, “type”: “fred”}, “three”: 3, “four”: 4}

instead of the expected

{“one”: “an elephant”, “two”: {“name”: “Fred”, “type”: “fred”, "aka": "glipglop"}, “three”: 3, “four”: 4}

Is the current result the expected behaviour of the update(j) function? If yes, what's the best way to achieve my expected result?

[nlohmann]

Right now, update is not implemented recursively: https://github.com/nlohmann/json/blob/develop/include/nlohmann/json.hpp#L5906-L5929

I think your expected behavior would be possible by recursively call update on all children.

[nlohmann]

Do you need further assistance with this issue?

[Batlan]

Thanks for fast reply at the time.
Unfortunately I thought I could quick fix a bug with the update function, now I will have to do it implement it myself using your suggestion and test it more thoroughly :-)