public virtual IKeyAndValue GetSmallest(IBTreeNode node, bool delete)
{
if (!node.IsLeaf())
{
var childTreeNode = node.GetChildAt(0, true);
if (childTreeNode.GetNbKeys() == _degree - 1)
{
node = PrepareForDelete(node, childTreeNode, 0);
}
childTreeNode = node.GetChildAt(0, true);
return(GetSmallest(childTreeNode, delete));
}
var keyAndValue = node.GetKeyAndValueAt(0);
if (delete)
{
node.DeleteKeyAndValueAt(0, true);
_persister.SaveNode(node);
}
return(keyAndValue);
}
public virtual IKeyAndValue GetBiggest(IBTreeNode node, bool delete)
{
var lastKeyIndex = node.GetNbKeys() - 1;
var lastChildIndex = node.GetNbChildren() - 1;
if (lastChildIndex > lastKeyIndex)
{
var child = node.GetChildAt(lastChildIndex, true);
if (child.GetNbKeys() == _degree - 1)
{
node = PrepareForDelete(node, child, lastChildIndex);
}
lastChildIndex = node.GetNbChildren() - 1;
child = node.GetChildAt(lastChildIndex, true);
return(GetBiggest(child, delete));
}
var kav = node.GetKeyAndValueAt(lastKeyIndex);
if (delete)
{
node.DeleteKeyAndValueAt(lastKeyIndex, false);
_persister.SaveNode(node);
}
return(kav);
}
private IBTreeNode PrepareForDelete(IBTreeNode parent, IBTreeNode child, int childIndex)
{
BTreeValidator.ValidateNode(parent);
BTreeValidator.ValidateNode(child);
// case 3a
IBTreeNode leftSibling = null;
IBTreeNode rightSibling = null;
if (childIndex > 0 && parent.GetNbChildren() > 0)
{
leftSibling = parent.GetChildAt(childIndex - 1, false);
}
if (childIndex < parent.GetNbChildren() - 1)
{
rightSibling = parent.GetChildAt(childIndex + 1, false);
}
// case 3a left
if (leftSibling != null && leftSibling.GetNbKeys() >= _degree)
{
var elementToMoveDown = parent.GetKeyAndValueAt(childIndex - 1);
var elementToMoveUp = leftSibling.GetLastKeyAndValue();
parent.SetKeyAndValueAt(elementToMoveUp, childIndex - 1);
child.InsertKeyAndValue(elementToMoveDown.GetKey(), elementToMoveDown.GetValue());
if (leftSibling.GetNbChildren() > leftSibling.GetNbKeys())
{
// Take the last child of the left sibling and set it the
// first child of the 'child' (incoming parameter)
// child.setChildAt(leftSibling.getChildAt(leftSibling.getNbChildren()
// - 1, true), 0);
child.SetChildAt(leftSibling, leftSibling.GetNbChildren() - 1, 0, true);
child.IncrementNbChildren();
}
leftSibling.DeleteKeyAndValueAt(leftSibling.GetNbKeys() - 1, false);
if (!leftSibling.IsLeaf())
{
leftSibling.DeleteChildAt(leftSibling.GetNbChildren() - 1);
}
_persister.SaveNode(parent);
_persister.SaveNode(child);
_persister.SaveNode(leftSibling);
if (OdbConfiguration.IsBTreeValidationEnabled())
{
BTreeValidator.ValidateNode(parent, parent == _root);
BTreeValidator.ValidateNode(child, false);
BTreeValidator.ValidateNode(leftSibling, false);
BTreeValidator.CheckDuplicateChildren(leftSibling, child);
}
return(parent);
}
// case 3a right
if (rightSibling != null && rightSibling.GetNbKeys() >= _degree)
{
var elementToMoveDown = parent.GetKeyAndValueAt(childIndex);
var elementToMoveUp = rightSibling.GetKeyAndValueAt(0);
parent.SetKeyAndValueAt(elementToMoveUp, childIndex);
child.InsertKeyAndValue(elementToMoveDown.GetKey(), elementToMoveDown.GetValue());
if (rightSibling.GetNbChildren() > 0)
{
// Take the first child of the right sibling and set it the
// last child of the 'child' (incoming parameter)
child.SetChildAt(rightSibling, 0, child.GetNbChildren(), true);
child.IncrementNbChildren();
}
rightSibling.DeleteKeyAndValueAt(0, true);
_persister.SaveNode(parent);
_persister.SaveNode(child);
_persister.SaveNode(rightSibling);
if (OdbConfiguration.IsBTreeValidationEnabled())
{
BTreeValidator.ValidateNode(parent, parent == _root);
BTreeValidator.ValidateNode(child, false);
BTreeValidator.ValidateNode(rightSibling, false);
BTreeValidator.CheckDuplicateChildren(rightSibling, child);
}
return(parent);
}
// case 3b
var isCase3B = (leftSibling != null && leftSibling.GetNbKeys() == _degree - 1) ||
(rightSibling != null && rightSibling.GetNbKeys() >= _degree - 1);
var parentWasSetToNull = false;
if (isCase3B)
{
// choose left sibling to execute merge
if (leftSibling != null)
{
var elementToMoveDown = parent.GetKeyAndValueAt(childIndex - 1);
leftSibling.InsertKeyAndValue(elementToMoveDown.GetKey(), elementToMoveDown.GetValue());
leftSibling.MergeWith(child);
parent.DeleteKeyAndValueAt(childIndex - 1, true);
if (parent.GetNbKeys() == 0)
{
// this is the root
if (!parent.HasParent())
{
_root = leftSibling;
_root.SetParent(null);
_height--;
parentWasSetToNull = true;
}
else
{
const string errorMessage = "Unexpected empty node that is node the root!";
throw new BTreeNodeValidationException(errorMessage);
}
}
else
{
parent.SetChildAt(leftSibling, childIndex - 1);
}
if (parentWasSetToNull)
{
_persister.DeleteNode(parent);
}
else
{
_persister.SaveNode(parent);
BTreeValidator.ValidateNode(parent, parent == _root);
}
// child was merged with another node it must be deleted
_persister.DeleteNode(child);
_persister.SaveNode(leftSibling);
// Validator.validateNode(child, child == root);
BTreeValidator.ValidateNode(leftSibling, leftSibling == _root);
// Validator.checkDuplicateChildren(leftSibling, child);
return(parentWasSetToNull
? _root
: parent);
}
// choose right sibling to execute merge
{
var elementToMoveDown = parent.GetKeyAndValueAt(childIndex);
child.InsertKeyAndValue(elementToMoveDown.GetKey(), elementToMoveDown.GetValue());
child.MergeWith(rightSibling);
parent.DeleteKeyAndValueAt(childIndex, true);
if (parent.GetNbKeys() == 0)
{
// this is the root
if (!parent.HasParent())
{
_root = child;
_root.SetParent(null);
_height--;
parentWasSetToNull = true;
}
else
{
throw new BTreeNodeValidationException("Unexpected empty root node!");
}
}
else
{
parent.SetChildAt(child, childIndex);
}
if (parentWasSetToNull)
{
_persister.DeleteNode(parent);
}
else
{
_persister.SaveNode(parent);
BTreeValidator.ValidateNode(parent, parent == _root);
}
_persister.DeleteNode(rightSibling);
_persister.SaveNode(child);
BTreeValidator.ValidateNode(child, child == _root);
// Validator.validateNode(rightSibling, rightSibling ==
// root);
// Validator.checkDuplicateChildren(rightSibling, child);
return(parentWasSetToNull
? _root
: parent);
}
}
throw new BTreeNodeValidationException("Unexpected case in executing prepare for delete");
}
/// <summary>
/// Returns the value of the deleted key
/// </summary>
/// <param name="node"> </param>
/// <param name="keyAndValue"> </param>
/// <returns> </returns>
/// <exception cref="System.Exception">System.Exception</exception>
private object InternalDelete(IBTreeNode node, IKeyAndValue keyAndValue)
{
var positionOfKey = node.GetPositionOfKey(keyAndValue.GetKey());
var keyIsHere = positionOfKey > 0;
if (node.IsLeaf())
{
if (keyIsHere)
{
var deletedValue = node.DeleteKeyForLeafNode(keyAndValue);
GetPersister().SaveNode(node);
return(deletedValue);
}
// key does not exist
return(null);
}
int realPosition;
if (!keyIsHere)
{
// descend
realPosition = -positionOfKey - 1;
var childTreeNode = node.GetChildAt(realPosition, true);
if (childTreeNode.GetNbKeys() == _degree - 1)
{
node = PrepareForDelete(node, childTreeNode, realPosition);
return(InternalDelete(node, keyAndValue));
}
return(InternalDelete(childTreeNode, keyAndValue));
}
// Here,the node is not a leaf and contains the key
realPosition = positionOfKey - 1;
var currentKey = node.GetKeyAt(realPosition);
var currentValue = node.GetValueAsObjectAt(realPosition);
// case 2a
var leftNode = node.GetChildAt(realPosition, true);
if (leftNode.GetNbKeys() >= _degree)
{
var prevKeyAndValue = GetBiggest(leftNode, true);
node.SetKeyAndValueAt(prevKeyAndValue, realPosition);
BTreeValidator.ValidateNode(node, node == _root);
GetPersister().SaveNode(node);
return(currentValue);
}
// case 2b
var rightNode = node.GetChildAt(realPosition + 1, true);
if (rightNode.GetNbKeys() >= _degree)
{
var nextKeyAndValue = GetSmallest(rightNode, true);
node.SetKeyAndValueAt(nextKeyAndValue, realPosition);
BTreeValidator.ValidateNode(node, node == _root);
GetPersister().SaveNode(node);
return(currentValue);
}
// case 2c
// Here, both left and right part have degree-1 keys
// remove the element to be deleted from node (shifting left all
// right
// elements, link to right link does not exist anymore)
// insert the key to be deleted in left child and merge the 2 nodes.
// rightNode should be deleted
// if node is root, then leftNode becomes the new root and node
// should be deleted
//
node.DeleteKeyAndValueAt(realPosition, true);
leftNode.InsertKeyAndValue(currentKey, currentValue);
leftNode.MergeWith(rightNode);
// If node is the root and is empty
if (!node.HasParent() && node.GetNbKeys() == 0)
{
_persister.DeleteNode(node);
_root = leftNode;
leftNode.SetParent(null);
// The height has been decreased. No need to save btree here.
// The calling delete method will save it.
_height--;
}
else
{
node.SetChildAt(leftNode, realPosition);
// Node must only be validated if it is not the root
BTreeValidator.ValidateNode(node, node == _root);
}
_persister.DeleteNode(rightNode);
BTreeValidator.ValidateNode(leftNode, leftNode == _root);
GetPersister().SaveNode(node);
GetPersister().SaveNode(leftNode);
return(InternalDelete(leftNode, keyAndValue));
}
