new ProxyEngine dispatches to multiple engines; contributed by jason pellerin

diff --git a/lib/sqlalchemy/ext/proxy.py b/lib/sqlalchemy/ext/proxy.py
new file mode 100644 (file)
index 0000000..ae5f40c
--- /dev/null
+++ b/lib/sqlalchemy/ext/proxy.py
@@ -0,0 +1,146 @@
+try:
+    from threading import local
+except ImportError:
+    from sqlalchemy.util import ThreadLocal as local
+
+from sqlalchemy import sql
+from sqlalchemy.engine import create_engine
+from sqlalchemy.types import TypeEngine
+
+import thread
+
+class ProxyEngine(object):
+    """
+    SQLEngine proxy. Supports lazy and late initialization by
+    delegating to a real engine (set with connect()), and using proxy
+    classes for TableImpl, ColumnImpl and TypeEngine.
+    """
+
+    def __init__(self):
+        # create the local storage for uri->engine map and current engine
+        self.storage = local()
+        self.storage.connection = {}
+        self.storage.engine = None
+        self.tables = {}
+            
+    def connect(self, uri, opts=None, **kwargs):
+        """Establish connection to a real engine.
+        """
+        key = "%s(%s,%s)" % (uri, repr(opts), repr(kwargs))
+        try:
+            map = self.storage.connection
+        except AttributeError:
+            self.storage.connection = {}
+            self.storage.engine = None
+            map = self.storage.connection
+        try:
+            self.engine = map[key]
+        except KeyError:
+            map[key] = create_engine(uri, opts, **kwargs)
+            self.storage.engine = map[key]
+            
+    def get_engine(self):
+        if self.storage.engine is None:
+            raise AttributeError('No connection established')
+        return self.storage.engine
+
+    def set_engine(self, engine):
+        self.storage.engine = engine
+        
+    engine = property(get_engine, set_engine)
+            
+    def hash_key(self):
+        return "%s(%s)" % (self.__class__.__name__, id(self))
+
+    def oid_column_name(self):
+        # NOTE: setting up mappers fails unless the proxy engine returns
+        # something for oid column name, and the call happens too early
+        # to proxy, so effecticely no oids are allowed when using
+        # proxy engine
+        return None
+    
+    def columnimpl(self, column):
+        """Proxy point: return a ProxyColumnImpl
+        """
+        return ProxyColumnImpl(self, column)
+
+    def tableimpl(self, table):
+        """Proxy point: return a ProxyTableImpl
+        """
+        return ProxyTableImpl(self, table)
+        
+    def type_descriptor(self, typeobj):
+        """Proxy point: return a ProxyTypeEngine 
+        """
+        return ProxyTypeEngine(self, typeobj)
+
+    def __getattr__(self, attr):
+        # call get_engine() to give subclasses a chance to change
+        # connection establishment behavior
+        if self.get_engine() is not None:
+            return getattr(self.engine, attr)
+        raise AttributeError('No connection established in ProxyEngine: '
+                             ' no access to %s' % attr)
+
+class ProxyColumnImpl(sql.ColumnImpl):
+    """Proxy column; defers engine access to ProxyEngine
+    """
+    def __init__(self, engine, column):
+        sql.ColumnImpl.__init__(self, column)
+        self._engine = engine
+
+    engine = property(lambda self: self._engine.engine)
+
+class ProxyTableImpl(sql.TableImpl):
+    """Proxy table; defers engine access to ProxyEngine
+    """
+    def __init__(self, engine, table):
+        sql.TableImpl.__init__(self, table)
+        self._engine = engine
+
+    engine = property(lambda self: self._engine.engine)
+
+class ProxyTypeEngine(object):
+    """Proxy type engine; defers engine access to ProxyEngine
+    """
+    def __init__(self, engine, typeobj):
+        self._engine = engine
+        self.typeobj = typeobj
+        
+    engine = property(lambda self: self._engine.engine)    
+
+    def __getattr__(self, attr):
+        # NOTE:
+        # profiling so far indicates that caching the type_descriptor
+        # results is more trouble than it's worth
+        return getattr(self.engine.type_descriptor(self.typeobj), attr)
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