How to connect to heroku postgresql from dart app?

Question

I host my dart server in heroku. I provisioned heroku postgres for this app. I referenced the library postgres to access the data.

In this library the constructor for object PostgreSQLConnection requires three parameters: url, port and db name.

Heroku gives me just one connection string. I tried to pass different parts of this string to the constructor, but it failed:

SocketException: Failed host lookup: 'postgres://isbmdx...

This is my code:

import 'package:postgres/postgres.dart';

class DataAccess {
  static Future<Object> ProcessRequest() async {
    var valueFromHeroku =
        Platform.environment["DATABASE_URL"];

    var dbPort = 5432;
    var dbName = "d8hqb682glgsf0";

    var connection = PostgreSQLConnection(valueFromHeroku, dbPort, dbName);
    await connection.open();

    ...
  }
}

Any ideas?

Answer 1

您尝试使用外部道具并在云Web控制台中进行配置，例如DATABASE_URL = $（heroku config：get DATABASE_URL -your-app）your_process

Answer 2

The format of the connection string provided via DATABASE_URL in heroku is the following:

postgres://<USER>:<PASSWORD>@<DATABASE_HOST>:<PORT>/<DATABASE_NAME>

This is how the string can be parsed in dart:

class PostgresInstance {
  final String host;
  final int port;
  final String database;
  final String user;
  final String password;

  PostgresInstance(
      this.host, this.port, this.database, this.user, this.password);

  factory PostgresInstance.fromString(String connectionString) {
    RegExp pattern = RegExp(
        "^postgres:\\\/\\\/(?<user>[^:]*):(?<pass>[^@]*)@(?<host>[^:]*):(?<port>[^\\\/]*)\\\/(?<db>[^\/]*)\$");
    RegExpMatch match = pattern.firstMatch(connectionString);
    if (match == null)
      throw Exception("Could not parse Postgres connection string.");
    int port = int.parse(match.namedGroup('port'));

    return PostgresInstance(
      match.namedGroup('host'),
      port,
      match.namedGroup('db'),
      match.namedGroup('user'),
      match.namedGroup('pass'),
    );
  }
}

Here is the test to validate correctness:

  test('Parse connection string', () async {
    String conn = "postgres://user:password@a.bc.d:5555/db";
    PostgresInstance i = PostgresInstance.fromString(conn);
    expect(i.host, "a.bc.d");
    expect(i.port, 5555);
    expect(i.database, "db");
    expect(i.password, "password");
    expect(i.user, "user");
  });