Merge pull request #21 from mattack108/master

Allow env variable for database connection

dataset/__init__.py

@@ -1,3 +1,4 @@
+import os
 # shut up useless SA warning:
 import warnings
 warnings.filterwarnings(
@@ -10,10 +11,11 @@ from dataset.freeze.app import freeze
 __all__ = ['Database', 'Table', 'freeze', 'connect']
 
 
-def connect(url, reflectMetadata=True):
+def connect(url=None, reflectMetadata=True):
     """
-    Opens a new connection to a database. *url* can be any valid `SQLAlchemy engine URL`_. Returns
-    an instance of :py:class:`Database <dataset.Database>`. Set *reflectMetadata* to False if you
+    Opens a new connection to a database. *url* can be any valid `SQLAlchemy engine URL`_.
+    If *url* is not defined it will try to use *DATABASE_URL* from environment variable.
+    Returns an instance of :py:class:`Database <dataset.Database>`. Set *reflectMetadata* to False if you
     don't want the entire database schema to be pre-loaded. This significantly speeds up
     connecting to large databases with lots of tables.
     ::
@@ -22,4 +24,5 @@ def connect(url, reflectMetadata=True):
 
     .. _SQLAlchemy Engine URL: http://docs.sqlalchemy.org/en/latest/core/engines.html#sqlalchemy.create_engine
     """
+    url = os.environ.get('DATABASE_URL', url)
     return Database(url, reflectMetadata)

docs/quickstart.rst

@@ -23,6 +23,11 @@ To connect to a database you need to identify it by its `URL <http://docs.sqlalc
    # connecting to a PostgreSQL database
    db = dataset.connect('postgresql://scott:tiger@localhost:5432/mydatabase')
 
+It is also possible to define the `URL` as an environment variable called `DATABASE_URL`
+so you can initialize database connection without explicitly passing an `URL`::
+
+   db = dataset.connect()
+
 Depending on which database you're using, you may also have to install
 the database bindings to support that database. SQLite is included in
 the Python core, but PostgreSQL requires ``psycopg2`` to be installed. 

test/test_persistence.py

@@ -1,3 +1,4 @@
+import os
 import unittest
 from datetime import datetime
 
@@ -9,11 +10,19 @@ from sample_data import TEST_DATA
 class DatabaseTestCase(unittest.TestCase):
 
     def setUp(self):
-        self.db = connect('sqlite:///:memory:')
+        os.environ['DATABASE_URL'] = 'sqlite:///:memory:'
+        self.db = connect()
         self.tbl = self.db['weather']
         for row in TEST_DATA:
             self.tbl.insert(row)
 
+    def tearDown(self):
+        # ensure env variable was unset
+        del os.environ['DATABASE_URL']
+
+    def test_valid_database_url(self):
+        assert self.db.url, os.environ['DATABASE_URL']
+
     def test_tables(self):
         assert self.db.tables == ['weather'], self.db.tables