jsoncpp. find object in array by matching value

Question

I have this JSON object:

{"books":[
    {
      "author" : "Petr",
      "book_name" : "Test1",
      "pages" : 200,
      "year" : 2002
    },
    {
      "author" : "Petr",
      "book_name" : "Test2",
      "pages" : 0,
      "year" : 0
    },
    {
      "author" : "STO",
      "book_name" : "Rocks",
      "pages" : 100,
      "year" : 2002
    }
  ]
}   

For example, I need to find a book(s) which author key is equal to Petr. How can I do this? Right now I have this piece of code:

Json::Value findBook(){
    Json::Value root = getRoot();

    cout<<root["books"].toStyledString()<<endl; //Prints JSON array of books mentioned above

    string searchKey;
    cout<<"Enter search key: ";
    cin>>searchKey;

    string searchValue;
    cout<<"Enter search value: ";
    cin>>searchValue;

    Json::Value foundBooks = root["books"]???; // How can I get here a list of books where searchKey is equal to searchValue?
}

Thanks in advance.

Answer 1

Something like this should do:

std::vector<Json::Value> booksByPeter(const Json::Value& root) {
    std::vector<Json::Value> res;
    for (const Json::Value& book : root["books"])  // iterate over "books"
    {
        if (book["author"].asString() == "Petr")   // if by "Petr"
        {
            res.push_back(book);                   // take a copy
        }
    }
    return res;                                    // and return
}

If not C++11, will instead have to do:

const Json::Value& books = root["books"];
for (Json::ValueConstIterator it = books.begin(); it != books.end(); ++it)
{
    const Json::Value& book = *it;
    // rest as before
}

Answer 2

You can iterate over JSON arrays as STL containers:

std::vector<Json::Value> SearchInArray(const Json::Value &json, const std::string &key, const std::string &value)
{
    assert(json.isArray());
    std::vector<Json::Value> results;
    for (size_t i = 0; i != json.size(); i++)
        if (json[i][key].asString() == value)
            results.push_back(json[i]);
    return results;
}

Use it like this:

std::vector<Json::Value> results = SearchInArray(json["books"], "author", "Petr");