Changes between Initial Version and Version 1 of CookBookTreeStructure

Timestamp:

Apr 2, 2006, 1:27:42 PM (20 years ago)

Author:

boxed@…

Comment:

--

CookBookTreeStructure

@@ +1 @@
+First of all there needs to be support for a pre-commit handler if you're using the 0.9x versions of django. The patch for this is:
+{{{
+Index: django/core/meta/__init__.py
+===================================================================
+--- django/core/meta/__init__.py        (revision 2013)
++++ django/core/meta/__init__.py        (working copy)
+@@ -1026,6 +1026,11 @@
+             ','.join(placeholders)), db_values)
+         if opts.has_auto_field and not pk_set:
+             setattr(self, opts.pk.attname, db.get_last_insert_id(cursor, opts.db_table, opts.pk.column))
++
++    # Run any pre-commit hooks.
++    if hasattr(self, '_pre_commit'):
++        self._pre_commit(opts, cursor)
++    
+     db.db.commit()
+     # Run any post-save hooks.
+     if hasattr(self, '_post_save'):
+@@ -1696,6 +1701,7 @@
+     man.save = curry(manipulator_save, opts, klass, add, change)
+     man.get_related_objects = curry(manipulator_get_related_objects, opts, klass, add, change)
+     man.flatten_data = curry(manipulator_flatten_data, opts, klass, add, change)
++    man.Klass = klass
+     for field_name_list in opts.unique_together:
+         setattr(man, 'isUnique%s' % '_'.join(field_name_list), curry(manipulator_validator_unique_together, field_name_list, opts))
+     for f in opts.fields:
+}}}
+
+Create helper methods for iterating through the parents (like in [wiki:CookBookCategoryDataModel A "category" data model] but I made it more general to avoid code duplication):
+{{{
+def foo_recurse_list(obj, parent_field, value_field):
+    parent_list = []
+    try:
+        if getattr(obj, 'parent_'+parent_field+'_id'):
+            p = getattr(obj, 'get_parent_'+parent_field)()
+            if value_field:
+                f = getattr(p, value_field)
+                parent_list.append(f)
+            else:
+                parent_list.append(p)
+            more = recurse_list(p, parent_field, value_field)
+            parent_list.extend(more)
+    finally:
+        return parent_list
+
+def recurse_list(obj, parent_field, value_field):
+    parent_list = foo_recurse_list(obj, parent_field, value_field)
+    parent_list.reverse()
+    return parent_list
+}}}
+
+In your model you will have a foreign key pointing to the parent element of each element and a character field that will be used to store the structure (called "cache_hierarchy" in my code). Then add a _pre_commit handler like this:
+{{{
+    def _pre_commit(self, opts, cursor):
+        # TODO: import above and remove this import line when django gets the no-magic patches
+        from where_ever_you_put_the_code_above import recurse_list
+        parent_list = recurse_list(self, 'your_model_name_here', 'id')
+        if self.id in parent_list:
+            raise 'Cannot be a child of itself'
+        
+        parent_list.append(self.id)
+
+        self.cache_hierarchy = '/'.join([str(i) for i in parent_list])
+        
+        cursor.execute("UPDATE %s SET cache_hierarchy = %%s WHERE id=%%s" % (db.quote_name(opts.db_table)), [self.cache_hierarchy, self.id])
+}}}