Add connection Class

bigchaindb/__init__.py

@@ -15,6 +15,7 @@ config = {
         'threads': None,  # if none, the value will be cpu_count * 2 + 1
     },
     'database': {
+        'backend': 'rethinkdb',
         'host': os.environ.get('BIGCHAINDB_DATABASE_HOST', 'localhost'),
         'port': 28015,
         'name': 'bigchain',

bigchaindb/backend/__init__.py

@@ -0,0 +1 @@
+from bigchaindb.backend.connection import connect  # noqa

bigchaindb/backend/connection.py

@@ -0,0 +1,15 @@
+from importlib import import_module
+
+BACKENDS = {
+    'rethinkdb': 'bigchaindb.backend.rethinkdb.connection.RethinkDBConnection'
+}
+
+
+def connect(backend, host, port, dbname):
+    module_name, _, class_name = BACKENDS[backend].rpartition('.')
+    Class = getattr(import_module(module_name), class_name)
+    return Class(host, port, dbname)
+
+
+class Connection:
+    pass

bigchaindb/backend/rethinkdb/connection.py

@@ -0,0 +1,64 @@
+import time
+import logging
+
+import rethinkdb as r
+
+import bigchaindb
+from bigchaindb.backend.connection import Connection
+
+logger = logging.getLogger(__name__)
+
+
+class RethinkDBConnection(Connection):
+    """This class is a proxy to run queries against the database,
+    it is:
+    - lazy, since it creates a connection only when needed
+    - resilient, because before raising exceptions it tries
+      more times to run the query or open a connection.
+    """
+
+    def __init__(self, host=None, port=None, db=None, max_tries=3):
+        """Create a new Connection instance.
+
+        Args:
+            host (str, optional): the host to connect to.
+            port (int, optional): the port to connect to.
+            db (str, optional): the database to use.
+            max_tries (int, optional): how many tries before giving up.
+        """
+
+        self.host = host or bigchaindb.config['database']['host']
+        self.port = port or bigchaindb.config['database']['port']
+        self.db = db or bigchaindb.config['database']['name']
+        self.max_tries = max_tries
+        self.conn = None
+
+    def run(self, query):
+        """Run a query.
+
+        Args:
+            query: the RethinkDB query.
+        """
+
+        if self.conn is None:
+            self._connect()
+
+        for i in range(self.max_tries):
+            try:
+                return query.run(self.conn)
+            except r.ReqlDriverError as exc:
+                if i + 1 == self.max_tries:
+                    raise
+                else:
+                    self._connect()
+
+    def _connect(self):
+        for i in range(self.max_tries):
+            try:
+                self.conn = r.connect(host=self.host, port=self.port,
+                                      db=self.db)
+            except r.ReqlDriverError as exc:
+                if i + 1 == self.max_tries:
+                    raise
+                else:
+                    time.sleep(2**i)

tests/backend/test_connection.py

@@ -0,0 +1,15 @@
+def test_get_connection_returns_the_correct_instance():
+    from bigchaindb.backend import connect
+    from bigchaindb.backend.connection import Connection
+    from bigchaindb.backend.rethinkdb.connection import RethinkDBConnection
+
+    config = {
+        'backend': 'rethinkdb',
+        'host': 'localhost',
+        'port': 28015,
+        'dbname': 'test'
+    }
+
+    conn = connect(**config)
+    assert isinstance(conn, Connection)
+    assert isinstance(conn, RethinkDBConnection)