json_replace.md

jsoncons::jsonpath::json_replace

#include <jsoncons_ext/jsonpath/json_query.hpp>

template<class Json, class T>
void json_replace(Json& root, 
                  const typename Json::string_view_type& path, 
                  T&& new_value)

Searches for all values that match a JSONPath expression and replaces them with the specified value

Parameters

root	JSON value
path	JSONPath expression string
new_value	The value to use as replacement

Exceptions

Throws a jsonpath_error if JSONPath evaluation fails.

Examples

Change the price of a book

Input JSON file booklist.json:

{ "store": {
    "book": [ 
      { "category": "reference",
        "author": "Nigel Rees",
        "title": "Sayings of the Century",
        "price": 8.95
      },
      { "category": "fiction",
        "author": "Evelyn Waugh",
        "title": "Sword of Honour",
        "price": 12.99
      },
      { "category": "fiction",
        "author": "Herman Melville",
        "title": "Moby Dick",
        "isbn": "0-553-21311-3",
        "price": 8.99
      }
    ]
  }
}

#include <jsoncons/json.hpp>
#include <jsoncons_ext/jsonpath/jsonpath.hpp>

using namespace jsoncons;
using namespace jsoncons::jsonpath;

int main()
{
    std::ifstream is("input/booklist.json");
    json booklist;
    is >> booklist;

    // Change the price of "Moby Dick"
    json_replace(booklist,"$.store.book[?(@.isbn == '0-553-21311-3')].price",10.0);
    std::cout << pretty_print(booklist) << std::endl;

}

Output:

{
    "store": {
        "book": [
            {
                "author": "Nigel Rees",
                "category": "reference",
                "price": 8.95,
                "title": "Sayings of the Century"
            },
            {
                "author": "Evelyn Waugh",
                "category": "fiction",
                "price": 12.99,
                "title": "Sword of Honour"
            },
            {
                "author": "Herman Melville",
                "category": "fiction",
                "isbn": "0-553-21311-3",
                "price": 10.0,
                "title": "Moby Dick"
            }
        ]
    }
}