tree ，hibernate, db hierarchical

tree 结构很常见，当persist 到数据库中。

有些操作，在db 中更好。

1。取得所有的叶子节点。

SELECT Name FROM Projects p WHERE NOT EXISTS( SELECT * FROM Projects WHERE Parent=p.VertexId)

2。multilevel operation ，用数据库的辅助表， 用triger 。

CREATE TABLE ProjectPaths(



VertexId INTEGER,



Depth INTEGER,



Path VARCHAR(300) 。







)

3. 用 hibernate 时，如果 stack over flow,考虑用 stack 代替recursive algrithm

public void traverseDepthFirst( AST ast )

{

//  Root AST node cannot be null or

//  traversal of its subtree is impossible.

if ( ast == null )

{

throw new IllegalArgumentException(

"node to traverse cannot be null!" );

}

//  Map to hold parents of each

//  AST node.  Unfortunately the AST

//  interface does not provide a method

//  for finding the parent of a node, so

//  we use the Map to save them.



Map parentNodes = new HashMap();



//  Start tree traversal with first child

//  of the specified root AST node.



AST currentNode = ast.getFirstChild();



//  Remember parent of first child.



parentNodes.put( currentNode , ast );



//  Iterate through nodes, simulating

//  recursive tree traversal, and add them

//  to queue in proper order for later

//  linear traversal.  This "flattens" the

//  into a linear list of nodes which can

//  be visited non-recursively.



while ( currentNode != null )

{

//  Visit the current node.



strategy.visit( currentNode );



//  Move down to current node's first child

//  if it exists.



AST childNode   = currentNode.getFirstChild();



//  If the child is not null, make it

//  the current node.



if ( childNode != null )

{

//  Remember parent of the child.



parentNodes.put( childNode , currentNode );



//  Make child the current node.



currentNode = childNode;



continue;

}



while ( currentNode != null )

{

//  Move to next sibling if any.



AST siblingNode = currentNode.getNextSibling();



if ( siblingNode != null )

{

//  Get current node's parent.

//  This is also the parent of the

//  sibling node.



AST parentNode  = (AST)parentNodes.get( currentNode );



//  Remember parent of sibling.



parentNodes.put( siblingNode , parentNode );



//  Make sibling the current node.



currentNode     = siblingNode;



break;

}

//  Move up to parent if no sibling.

//  If parent is root node, we're done.



currentNode = (AST)parentNodes.get( currentNode );



if ( currentNode.equals( ast ) )

{

currentNode = null;

}

}

}
 
 

参考:

http://wordhoard.northwestern.edu/userman/hibernatechanges.html

《Tansact Sql cookbook.》








西津渡