Dart: convert map into query string

user_892029 0
Viewed 8961

I have a situation where I need to turn a Map into a query String (after the first ?). For instance if I have the following map:

Map json = {
    "email":  eml,
    "password": passwd
};

And a base URL:

String baseURL = "http://localhost:8080/myapp";

Then I need something that converts the json Map into the query string of the base URL:

String fullURL = parameterizeURL(baseURL, json);

// Prints: http://localhost:8080/myapp?email=blah&password=meh
// (if "blah" was entered as the email, and "meh" was entered as the password)
print(fullURL);

I found this query String-to-map library on Git, but I need the inverse of this! It would be great to get URL encoding in there as well.

I'm happy to make something homegrown but being so new to Dart I was wondering if there's anything on pub/Github/the etherspehere that does this already.

dart query-string url type-conversion map
9 Answers

TL;DR

String queryString = Uri(queryParameters: {'x': '1', 'y': '2'}).query;

print(queryString); // x=1&y=2
user_22895140 
final yourMap = {'x': '1', 'y': '2'};
final queryString = yourMap.toMap().entries.map((e) => '${e.key}=${e.value}').join('&');
print(queryString); // x=1&y=2
user_167707500

i wrote a recursive function to turn any Map<String, dynamic> to query String.

String getQueryString(Map params, {String prefix: '&', bool inRecursion: false}) {

    String query = '';

    params.forEach((key, value) {

        if (inRecursion) {
            key = '[$key]';
        }

        if (value is String || value is int || value is double || value is bool) {
            query += '$prefix$key=$value';
        } else if (value is List || value is Map) {
            if (value is List) value = value.asMap();
            value.forEach((k, v) {
                query += getQueryString({k: v}, prefix: '$prefix$key', inRecursion: true);
            });
        }
   });

   return query;
}

example:

Map<String, dynamic> params = {'aa': 1.1, 'bb': [2, [3, ['5', {'66': 777}]]]};
String query = getQueryString(params);
print(query);

this code will print:

&aa=1.1&bb[0]=2&bb[1][0]=3&bb[1][1][0]=5&bb[1][1][1][66]=777
user_102544310
user_6605720

I faced the same problem and wrote this function for me. Here it is in case someone needs it:

String makeQuery(Map<String, dynamic>? data) {
  var result = [];

  if (data != null) {
    data.forEach((key, value) {
      if (value != null && (value is! String || value.trim().isNotEmpty)) {
        result.add('$key=${value.toString()}');
      }
    });
  }

  return result.join('&');
}
user_9818200

I think that the easiest way to to generate a query string from a Map is to use Uri.replace. It's basically the same thing as using the Uri constructor, but it avoids needing to manually copy all of the other parts of the URL:

String baseURL = "http://localhost:8080/myapp";

Map json = {
  "email":  eml,
  "password": passwd
};

String fullURL = Uri.parse(baseURL).replace(queryParameters: json).toString();

I realize that I'm responding to an old question, but I feel compelled to additionally point out that you probably shouldn't be sending passwords via query strings.

user_1797150

This is my own function that will escape the parameters that have null value

String generateQueryString(Map<String, dynamic> params) {
    List queryString = [];
    params.forEach((key, value) {
      if (value != null) {
        queryString.add(key + '=' + value.toString());
      }
    });
    return queryString.join('&');
  }

  String query = generateQueryString({
    'CategoryId': '1',
    'MinAmount': 0,
    'MaxAmount': 2012,
    'Quantity': 1,
  });

  print(query); // CategoryId=1&MinAmount=0&MaxAmount=2012&Quantity=1
user_25831750
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