Allow multiple plugin names

The :class:`.URL` object now allows query keys to be specified multiple
times where their values will be joined into a list.  This is to support
the plugins feature documented at :class:`.CreateEnginePlugin` which
documents that "plugin" can be passed multiple times. Additionally, the
plugin names can be passed to :func:`.create_engine` outside of the URL
using the new :paramref:`.create_engine.plugins` parameter.

Change-Id: Ifc48ad120bd6c6204eda567492caf79832aeeaa5
Fixes: #4170

4 files changed, 37 insertions, 5 deletions

diff --git a/lib/sqlalchemy/engine/__init__.py b/lib/sqlalchemy/engine/__init__.py
index 7ecc46a92..841dc405e 100644
--- a/lib/sqlalchemy/engine/__init__.py
+++ b/lib/sqlalchemy/engine/__init__.py
@@ -398,6 +398,11 @@ def create_engine(*args, **kwargs):
         up on getting a connection from the pool. This is only used
         with :class:`~sqlalchemy.pool.QueuePool`.
 
+    :param plugins: string list of plugin names to load.  See
+        :class:`.CreateEnginePlugin` for background.
+
+        .. versionadded:: 1.2.3
+
     :param strategy='plain': selects alternate engine implementations.
         Currently available are:
 
diff --git a/lib/sqlalchemy/engine/interfaces.py b/lib/sqlalchemy/engine/interfaces.py
index b9efce92e..9c3b24e9a 100644
--- a/lib/sqlalchemy/engine/interfaces.py
+++ b/lib/sqlalchemy/engine/interfaces.py
@@ -844,6 +844,16 @@ class CreateEnginePlugin(object):
         engine = create_engine(
           "mysql+pymysql://scott:tiger@localhost/test?plugin=myplugin")
 
+    Alternatively, the :paramref:`.create_engine.plugins" argument may be
+    passed as a list to :func:`.create_engine`::
+
+        engine = create_engine(
+          "mysql+pymysql://scott:tiger@localhost/test",
+          plugins=["myplugin"])
+
+    .. versionadded:: 1.2.3  plugin names can also be specified
+       to :func:`.create_engine` as a list
+
     The ``plugin`` argument supports multiple instances, so that a URL
     may specify multiple plugins; they are loaded in the order stated
     in the URL::
diff --git a/lib/sqlalchemy/engine/strategies.py b/lib/sqlalchemy/engine/strategies.py
index aff1dd360..4b6ee77fd 100644
--- a/lib/sqlalchemy/engine/strategies.py
+++ b/lib/sqlalchemy/engine/strategies.py
@@ -52,6 +52,7 @@ class DefaultEngineStrategy(EngineStrategy):
         plugins = u._instantiate_plugins(kwargs)
 
         u.query.pop('plugin', None)
+        kwargs.pop('plugins', None)
 
         entrypoint = u._get_entrypoint()
         dialect_cls = entrypoint.get_dialect_cls(u)
diff --git a/lib/sqlalchemy/engine/url.py b/lib/sqlalchemy/engine/url.py
index 483d40703..1662efe20 100644
--- a/lib/sqlalchemy/engine/url.py
+++ b/lib/sqlalchemy/engine/url.py
@@ -83,7 +83,12 @@ class URL(object):
         if self.query:
             keys = list(self.query)
             keys.sort()
-            s += '?' + "&".join("%s=%s" % (k, self.query[k]) for k in keys)
+            s += '?' + "&".join(
+                "%s=%s" % (
+                    k,
+                    element
+                ) for k in keys for element in util.to_list(self.query[k])
+            )
         return s
 
     def __str__(self):
@@ -130,6 +135,7 @@ class URL(object):
 
     def _instantiate_plugins(self, kwargs):
         plugin_names = util.to_list(self.query.get('plugin', ()))
+        plugin_names += kwargs.get('plugins', [])
 
         return [
             plugins.load(plugin_name)(self, kwargs)
@@ -230,10 +236,20 @@ def _parse_rfc1738_args(name):
         if components['database'] is not None:
             tokens = components['database'].split('?', 2)
             components['database'] = tokens[0]
-            query = (
-                len(tokens) > 1 and dict(util.parse_qsl(tokens[1]))) or None
-            if util.py2k and query is not None:
-                query = {k.encode('ascii'): query[k] for k in query}
+
+            if len(tokens) > 1:
+                query = {}
+
+                for key, value in util.parse_qsl(tokens[1]):
+                    if util.py2k:
+                        key = key.encode('ascii')
+                    if key in query:
+                        query[key] = util.to_list(query[key])
+                        query[key].append(value)
+                    else:
+                        query[key] = value
+            else:
+                query = None
         else:
             query = None
         components['query'] = query