Is it possible to have a source json where you copy a subkey to a new json?

[jasonmnemonic]

Hi Daniel.

Thanks for the great library and hard work. It is a cool library. ;-)

A question on json and maybe anyone can answer this (thanks):

Say, I have a source json:

{
        "nameid":1,
        "name":"platypus",
        "postcode":1,
        "previous-postcode":
            {
                "postcode1":0,
                "postcode2": 5,
                "postcode3": 9
            }
}

When I make a new jsoncons::json originalJsonDoc using json::parse to parse the string above. Next, I create a new jsoncons:json newJsonDoc that is empty.

In my new json, I am interested to newJsonDoc[ "previous-postcode" ] = jsonRoot[ "previous-postcode" ].to_string(); but this returns me a string like {"previous-postcode": "{ \"postcode1\":0, \"postcode2\":5, \"postcode2\":9 }"}.

Is there a way to do something like newJsonDoc[ "previous-postcode" ] = jsonRoot[ "previous-postcode" ] so that when I dump-pretty, I will get {"previous-postcode": {"postcode1":0, "postcode2":5, "postcode3":9 }}.

I think there is a way but I am having trouble to locate it.

Thank you! ;-)

[danielaparker]

The assignment

newJsonDoc["previous-postcode"] = jsonRoot["previous-postcode"];

should have worked, but there seems to be a defect for the assignment overload such that this doesn't compile. For non const json values, the bracket notation actually returns a proxy, and the assignment operator on the proxy appears to have an issue with overloads. I need to look at that.

But you can do either of these:

newJsonDoc["previous-postcode"] = originalJsonDoc.at("previous-postcode");

newJsonDoc.try_emplace("previous-postcode", originalJsonDoc.at("previous-postcode"));

Both will give you

{"previous-postcode":{"postcode1":0,"postcode2":5,"postcode3":9}}

(The second is more efficient.)

[jasonmnemonic]

Thanks Daniel for the fast reply! :-)

Another question, will both the operations .at and .try_emplace cause a move operation? I mean I would like the keep the original json structure unchanged (not removed).

Ta.

[danielaparker]

No. For a move operation, you would have to explicitly write

newJsonDoc["previous-postcode"] = std::move(originalJsonDoc.at("previous-postcode"));

newJsonDoc.try_emplace("previous-postcode", std::move(originalJsonDoc.at("previous-postcode")));

[jasonmnemonic]

Thanks Dan. Sorry, I think I asked a wrong question.

I mean if I want to avoid a move operation where I want to copy contents i.e. after doing newJsonDoc.try_emplace("previous-postcode", originalJsonDoc.at("previous-postcode")); I would like the "previous-postcode" node to still exist in originalJsonDoc.

I had a look at the code, I think newJsonDoc["previous-postcode"] = originalJsonDoc.at("previous-postcode"); or try-emplace should be OK the operator= initialises from the other.

If I read it wrongly, please correct me. Thank you.

[danielaparker]

Regarding "I would like the "previous-postcode" node to still exist in originalJsonDoc", it will,

newJsonDoc["previous-postcode"] = originalJsonDoc.at("previous-postcode");

newJsonDoc.try_emplace("previous-postcode", originalJsonDoc.at("previous-postcode"));

make copies, they do not move.