PostgreSQL database driver for Dart

Basic usage

Obtaining a connection

var uri = 'postgres://username:password@localhost:5432/database';
connect(uri).then((conn) {
    // ...
});

SSL connections

Set the sslmode to require by appending this to the connection uri. This driver only supports sslmode=require, if sslmode is ommitted the driver will always connect without using SSL.

var uri = 'postgres://username:password@localhost:5432/database?sslmode=require';
connect(uri).then((conn) {
    // ...
});

Querying

conn.query('select color from crayons').toList().then((rows) {
    for (var row in rows) {
        print(row.color); // Refer to columns by name,
        print(row[0]);    // Or by column index.
    }
});

Executing

conn.execute("update crayons set color = 'pink'").then((rowsAffected) {
    print(rowsAffected);
});

Query Parameters

Query parameters can be provided using a map. Strings will be escaped to prevent SQL injection vulnerabilities.

conn.query('select color from crayons where id = @id', {'id': 5})
  .toList()
    .then((result) { print(result); });

conn.execute('insert into crayons values (@id, @color)',
             {'id': 1, 'color': 'pink'})
    .then((_) { print('done.'); });

Closing the connection

You must remember to call Connection.close() when you're done. This won't be done automatically for you.

Conversion of Postgresql datatypes.

Below is the mapping from Postgresql types to Dart types. All types which do not have an explicit mapping will be returned as a String in Postgresql's standard text format. This means that it is still possible to handle all types, as you can parse the string yourself.

     Postgresql type                 Dart type
    boolean                         bool
    int2, int4, int8                int
    float4, float8                  double
    numeric                         String
    timestamp, timestamptz, date    Datetime
    json, jsonb                     Map/List
    All other types                 String

Mapping the results of a query to an object

class Crayon {
    String color;
    int length;
}

conn.query('select color, length from crayons')
    .map((row) => new Crayon()
                         ..color = row.color
                         ..length = row.length)
    .toList()
    .then((List<Crayon> crayons) {
        for (var c in crayons) {
            print(c is Crayon);
            print(c.color);
            print(c.length);
        }
    });

Or for an immutable object:

class ImmutableCrayon {
    ImmutableCrayon(this.color, this.length);
    final String color;
    final int length;
}

conn.query('select color, length from crayons')
  .map((row) => new ImmutableCrayon(row.color, row.length))
     .toList()
    .then((List<ImmutableCrayon> crayons) {
        for (var c in crayons) {
            print(c is ImmutableCrayon);
            print(c.color);
            print(c.length);
        }
    });

Query queueing

Queries are queued and executed in the order in which they were queued.

So if you're not concerned about handling errors, you can write code like this:

conn.execute("create table crayons (color text, length int)");
conn.execute("insert into crayons values ('pink', 5)");
conn.query("select color from crayons").single.then((crayon) {
    print(crayon.color); // prints 'pink'
});

Query streaming

Connection.query() returns a Stream of results. You can use each row as soon as it is received, or you can wait till they all arrive by calling Stream.toList().

Connection pooling

In server applications, a connection pool can be used to avoid the overhead of obtaining a connection for each request.

import 'package:postgresql/pool.dart';

main() {
  var uri = 'postgres://username:password@localhost:5432/database';
  var pool = new Pool(uri, minConnections: 2, maxConnections: 5);
  pool.messages.listen(print);
  pool.start().then((_) {
    print('Min connections established.');
    pool.connect().then((conn) { // Obtain connection from pool
      conn.query("select 'oi';")
        .toList()
        .then(print)
        .then((_) => conn.close()) // Return connection to pool
        .catchError((err) => print('Query error: $err'));
    });
  });
}

Example program

Add postgresql to your pubspec.yaml file, and run pub install.

name: postgresql_example
dependencies:
  postgresql: any

import 'package:postgresql/postgresql.dart';

void main() {
  var uri = 'postgres://testdb:password@localhost:5432/testdb';
  var sql = "select 'oi'"; 
  connect(uri).then((conn) {
    conn.query(sql).toList()
        .then((result) {
            print('result: $result');
        })
        .whenComplete(() {
            conn.close();
        });
  });
}

Testing

To run the unit tests you will need to create a database, and edit 'test/config.yaml' accordingly.

Creating a database for testing

Change to the postgres user and run the administration commands.

sudo su postgres
createuser --pwprompt testdb
  Enter password for new role: password
  Enter it again: password
  Shall the new role be a superuser? (y/n) n
  Shall the new role be allowed to create databases? (y/n) n
  Shall the new role be allowed to create more new roles? (y/n) n
createdb --owner testdb testdb
exit

Check that it worked by logging in.