From 2cf79c386f814d6d6d34f8ec1fc20c2dca7e1aee Mon Sep 17 00:00:00 2001
From: Calen Pennington <cale@edx.org>
Date: Wed, 18 Mar 2015 14:11:29 -0400
Subject: [PATCH] Pass parent to xblock on load

---
 xblock/core.py              |  5 ++---
 xblock/field_data.py        |  3 +++
 xblock/mixins.py            | 42 ++++++++++++++++++++++++++++++++++++-
 xblock/runtime.py           |  6 +++---
 xblock/test/test_runtime.py |  3 ++-
 5 files changed, 51 insertions(+), 8 deletions(-)

diff --git a/xblock/core.py b/xblock/core.py
index 9121ab282..069a32363 100644
--- a/xblock/core.py
+++ b/xblock/core.py
@@ -136,7 +136,7 @@ def load_tagged_classes(cls, tag, fail_silently=True):
             if tag in class_._class_tags:
                 yield name, class_
 
-    def __init__(self, runtime, field_data=None, scope_ids=UNSET):
+    def __init__(self, runtime, field_data=None, scope_ids=UNSET, *args, **kwargs):
         """
         Construct a new XBlock.
 
@@ -153,13 +153,12 @@ def __init__(self, runtime, field_data=None, scope_ids=UNSET):
 
             scope_ids (:class:`.ScopeIds`): Identifiers needed to resolve
                 scopes.
-
         """
         if scope_ids is UNSET:
             raise TypeError('scope_ids are required')
 
         # Provide backwards compatibility for external access through _field_data
-        super(XBlock, self).__init__(runtime=runtime, scope_ids=scope_ids, field_data=field_data)
+        super(XBlock, self).__init__(runtime=runtime, scope_ids=scope_ids, field_data=field_data, *args, **kwargs)
 
     def render(self, view, context=None):
         """Render `view` with this block's runtime and the supplied `context`"""
diff --git a/xblock/field_data.py b/xblock/field_data.py
index d4e971705..fbe4680e0 100644
--- a/xblock/field_data.py
+++ b/xblock/field_data.py
@@ -199,3 +199,6 @@ def has(self, block, name):
 
     def default(self, block, name):
         return self._source.default(block, name)
+
+    def __repr__(self):
+        return "ReadOnlyFieldData({!r})".format(self._source)
diff --git a/xblock/mixins.py b/xblock/mixins.py
index a2ddadec5..04f282bbe 100644
--- a/xblock/mixins.py
+++ b/xblock/mixins.py
@@ -332,12 +332,19 @@ def __init__(self, **kwargs):
         # A cache of the parent block, retrieved from .parent
         self._parent_block = None
         self._parent_block_id = None
+        self._child_cache = {}
+
+        for_parent = kwargs.pop('for_parent', None)
+
+        if for_parent is not None:
+            self._parent_block = for_parent
+            self._parent_block_id = for_parent.scope_ids.usage_id
 
         super(HierarchyMixin, self).__init__(**kwargs)
 
     def get_parent(self):
         """Return the parent block of this block, or None if there isn't one."""
-        if self._parent_block_id != self.parent:
+        if not self.has_cached_parent:
             if self.parent is not None:
                 self._parent_block = self.runtime.get_block(self.parent)
             else:
@@ -345,6 +352,39 @@ def get_parent(self):
             self._parent_block_id = self.parent
         return self._parent_block
 
+    @property
+    def has_cached_parent(self):
+        """Return whether this block has a cached parent block."""
+        return self.parent is not None and self._parent_block_id == self.parent
+
+    def get_child(self, usage_id):
+        """Return the child identified by ``usage_id``."""
+        if usage_id in self._child_cache:
+            return self._child_cache[usage_id]
+
+        child_block = self.runtime.get_block(usage_id, for_parent=self)
+        self._child_cache[usage_id] = child_block
+        return child_block
+
+    def get_children(self, usage_id_filter=None):
+        """
+        Return instantiated XBlocks for each of this blocks ``children``.
+        """
+        if not self.has_children:
+            return []
+
+        return [
+            self.get_child(usage_id)
+            for usage_id in self.children
+            if usage_id_filter is None or usage_id_filter(usage_id)
+        ]
+
+    def clear_child_cache(self):
+        """
+        Reset the cache of children stored on this XBlock.
+        """
+        self._child_cache.clear()
+
 
 class XmlSerializationMixin(ScopedStorageMixin):
     """
diff --git a/xblock/runtime.py b/xblock/runtime.py
index c215ab28b..4a91239b9 100644
--- a/xblock/runtime.py
+++ b/xblock/runtime.py
@@ -123,7 +123,7 @@ def __init__(self, kvs, **kwargs):
         self._kvs = kvs
 
     def __repr__(self):
-        return "<{0.__class__.__name__} {0._kvs!r}>".format(self)
+        return "{0.__class__.__name__}({0._kvs!r})".format(self)
 
     def _getfield(self, block, name):
         """
@@ -635,7 +635,7 @@ def construct_xblock_from_class(self, cls, scope_ids, field_data=None, *args, **
             *args, **kwargs
         )
 
-    def get_block(self, usage_id):
+    def get_block(self, usage_id, for_parent=None):
         """
         Create an XBlock instance in this runtime.
 
@@ -647,7 +647,7 @@ def get_block(self, usage_id):
         except NoSuchDefinition:
             raise NoSuchUsage(repr(usage_id))
         keys = ScopeIds(self.user_id, block_type, def_id, usage_id)
-        block = self.construct_xblock(block_type, keys)
+        block = self.construct_xblock(block_type, keys, for_parent=for_parent)
         return block
 
     def get_aside(self, aside_usage_id):
diff --git a/xblock/test/test_runtime.py b/xblock/test/test_runtime.py
index 99e6e5642..280a960c6 100644
--- a/xblock/test/test_runtime.py
+++ b/xblock/test/test_runtime.py
@@ -646,7 +646,8 @@ def test_basic(self):
         self.id_reader.get_block_type.assert_called_with(self.def_id)
         self.construct_block.assert_called_with(
             self.block_type,
-            ScopeIds(self.user_id, self.block_type, self.def_id, self.usage_id)
+            ScopeIds(self.user_id, self.block_type, self.def_id, self.usage_id),
+            for_parent=None,
         )
 
     def test_missing_usage(self):