From 30f55a50165e56d79dfc5f720616d4d9cc400b33 Mon Sep 17 00:00:00 2001
From: Mike Bayer <mike_mp@zzzcomputing.com>
Date: Wed, 7 May 2008 14:48:04 +0000
Subject: [PATCH] - added an example dynamic_dict/dynamic_dict.py, illustrating
 a simple way to place dictionary behavior on top of a dynamic_loader.

---
 CHANGES                               |  4 ++
 examples/dynamic_dict/dynamic_dict.py | 83 +++++++++++++++++++++++++++
 2 files changed, 87 insertions(+)
 create mode 100644 examples/dynamic_dict/dynamic_dict.py

diff --git a/CHANGES b/CHANGES
index 6c2de28789..8ec857dadd 100644
--- a/CHANGES
+++ b/CHANGES
@@ -69,6 +69,10 @@ CHANGES
       their operands and only operate on sets, frozensets or
       subclasses of the collection type. Previously, they would
       accept any duck-typed set.
+      
+    - added an example dynamic_dict/dynamic_dict.py, illustrating
+      a simple way to place dictionary behavior on top of 
+      a dynamic_loader.
 
 - sql
     - Added COLLATE support via the .collate(<collation>)
diff --git a/examples/dynamic_dict/dynamic_dict.py b/examples/dynamic_dict/dynamic_dict.py
new file mode 100644
index 0000000000..682def78c3
--- /dev/null
+++ b/examples/dynamic_dict/dynamic_dict.py
@@ -0,0 +1,83 @@
+"""Illustrates how to place a dictionary-like facade on top of a dynamic_loader, so
+that dictionary operations (assuming simple string keys) can operate upon a large 
+collection without loading the full collection at once.
+
+This is something that may eventually be added as a feature to dynamic_loader() itself.
+
+Similar approaches could be taken towards sets and dictionaries with non-string keys 
+although the hash policy of the members would need to be distilled into a filter() criterion.
+
+"""
+
+class MyProxyDict(object):
+    def __init__(self, parent, collection_name, keyname):
+        self.parent = parent
+        self.collection_name = collection_name
+        self.keyname = keyname
+        
+    def collection(self):
+        return getattr(self.parent, self.collection_name)
+    collection = property(collection)
+    
+    def keys(self):
+        # this can be improved to not query all columns
+        return [getattr(x, self.keyname) for x in self.collection.all()]
+        
+    def __getitem__(self, key):
+        x = self.collection.filter_by(**{self.keyname:key}).first()
+        if x:
+            return x
+        else:
+            raise KeyError(key)
+
+    def __setitem__(self, key, value):
+        try:
+            existing = self[key]
+            self.collection.remove(existing)
+        except KeyError:
+            pass
+        self.collection.append(value)
+
+from sqlalchemy.ext.declarative import declarative_base
+from sqlalchemy import *
+from sqlalchemy.orm import *
+
+Base = declarative_base(engine=create_engine('sqlite://'))
+
+class MyParent(Base):
+    __tablename__ = 'parent'
+    id = Column(Integer, primary_key=True)
+    name = Column(String(50))
+    _collection = dynamic_loader("MyChild", cascade="all, delete-orphan")
+    
+    def child_map(self):
+        return MyProxyDict(self, '_collection', 'key')
+    child_map = property(child_map)
+    
+class MyChild(Base):
+    __tablename__ = 'child'
+    id = Column(Integer, primary_key=True)
+    key = Column(String(50))
+    parent_id = Column(Integer, ForeignKey('parent.id'))
+
+    
+Base.metadata.create_all()
+
+sess = create_session(autoflush=True, transactional=True)
+
+p1 = MyParent(name='p1')
+sess.save(p1)
+
+p1.child_map['k1'] = k1 = MyChild(key='k1')
+p1.child_map['k2'] = k2 = MyChild(key='k2')
+
+
+assert p1.child_map.keys() == ['k1', 'k2']
+
+assert p1.child_map['k1'] is k1
+
+p1.child_map['k2'] = k2b = MyChild(key='k2')
+assert p1.child_map['k2'] is k2b
+
+assert sess.query(MyChild).all() == [k1, k2b]
+
-- 
2.47.3