#Most efficient way to search for child parameters (recursive find?)

[JimAtCanon]

Hello All-

I have an application where I have a hierarchical set of JSON objects. Meaning that I have objects that in turn have child JSON objects and so on. I need to have the ability to allow the user to query the value of one of the objects using something akin to a file path. For example, example if my JSON object looks like:

{
         "One":1,
         "Two":2,
         "Child":{
                 "Child1":1
                 "Child2":2
                 }
         "Three":3
}

I want to provide a method that will return the value of any parameter by passing a 'path' to the parameter. Using the example above, if I wanted the value of the parameter "Child2", I could request it using the path 'Child/Child2', which would return the value 2. I have it working with the code below:

std::filesystem::path path(parameterPath);
for (const auto &parameterName : path) {
   nlohmann::json::iterator iterator = parameterValue.find(parameterName);
   if (iterator != parameterValue.end()) {
      parameterValue = *iterator; //  This makes a copy of the parameter, which is overkill, I just want a reference to it.
      }
     else {
         parameterValue.clear();
         break;
     }
}

However I suspect that this is inefficient because I am creating a copy of the parameters as I traverse the tree. I have also thought about iterators and pointers, but thought I would reach out to the community to to see if anyone has already solved this problem, hopefully in a more efficient manor.

Any suggestions?

Thanks!

Jim

[nlohmann]

The library supports JSON Pointer, see https://github.com/nlohmann/json#json-pointer-and-json-patch. You could write j["/Child/Child2"_json_pointer] to access the value you described with Child/Child2.

[nlohmann]

@JimAtCanon Does #1141 (comment) work for your use case?

[nlohmann]

@JimAtCanon Do you need further assistance?

[JimAtCanon]

Not on this topic, the JSON pointer worked. It would have been nice if there were an example of how to create a pointer with a string variable. All of the examples I found were using string constants postfixed with the '_json_pointer' it took me some digging to find the constructor for the json_pointer class. An example using string variables would have been helpful.

Thanks once again for an excellent library.

Jim

j_original["/baz/1"_json_pointer];

[nlohmann]

Thanks for checking back! And thanks for the hint - I shall add a paragraph to the documentation.