Can we use make_expression with mutable reference to update multiple Json Object?

[mapleFU]

Currently, jsonpath_expression type has a reference template argument. However, make_expression doesn't support construct with a mutable reference.

So:

1. Is it design to just replacing built same json path when json_query multiple objects?
2. How can we pre-build a jsonpath expression, and use it both to build and replace?

[danielaparker]

I've added a make_update_expression to master. It can be used to update the JSON document as follows:

    auto expr = jsoncons::jsonpath::make_update_expression<json>("$.books[*]");

    auto callback = [](const std::string& /*path*/, json& book)
    {
        if (book.at("category") == "memoir" && !book.contains("price"))
        {
            book.try_emplace("price", 140.0);
        }
    };

    json doc = json::parse(input);

    expr.evaluate_and_update(doc, callback);

    std::cout << pretty_print(doc) << std::endl;

It can also be used to query a JSON document with a callback that takes a const json& as a parameter:

    auto callback2 = [](const std::string& /*path*/, const json& book)
    {
        if (book.at("category") == "memoir" && !book.contains("price"))
        {
        }
    };

    expr.evaluate(doc, callback2);

With this way of constructing a jsonpath_expression, the document passed by reference to evaluate and evaluate_and_update must be non const.

I'll investigate whether the jsonpath_expression returned by the make_expression function can be generalized to support both passing a const reference to evaluate, and to support evaluate_and_update with a non const reference.

[mapleFU]

Thanks! Waiting for new release

[danielaparker]

This is supported in 0.172.0, see jsonpath_expression::update

[mapleFU]

Thanks!