Class SubstituteExpressionVisitor

java.lang.Object

org.apache.derby.impl.sql.compile.SubstituteExpressionVisitor

All Implemented Interfaces:

Visitor

class SubstituteExpressionVisitor
extends Object
implements Visitor

Replaces a source expression with a target expression.

Field Summary

Fields

Modifier and Type	Field	Description
private Class<?>	skipOverClass
private ValueNode	source
private ValueNode	target

Constructor Summary

Constructors

Constructor	Description
SubstituteExpressionVisitor(ValueNode s, ValueNode t, Class<?> skipThisClass)

Method Summary

Modifier and Type	Method	Description
(package private) ValueNode	getSource()	used by GroupByNode to process expressions by complexity level.
boolean	skipChildren(Visitable node)	Method that is called to indicate whether we should skip all nodes below this node for traversal.
boolean	stopTraversal()	Method that is called to see if query tree traversal should be stopped before visiting all nodes.
Visitable	visit(Visitable node)	This is the default visit operation on a QueryTreeNode.
boolean	visitChildrenFirst(Visitable node)	Method that is called to see if visit() should be called on the children of node before it is called on node itself.

Methods inherited from class Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Details

source

private ValueNode source

target

private ValueNode target

skipOverClass

private Class<?> skipOverClass

Constructor Details

SubstituteExpressionVisitor

SubstituteExpressionVisitor(ValueNode s,
 ValueNode t,
 Class<?> skipThisClass)

Method Details

getSource

ValueNode getSource()

used by GroupByNode to process expressions by complexity level.

visit

public Visitable visit(Visitable node)
                throws StandardException

Description copied from interface: Visitor

This is the default visit operation on a QueryTreeNode. It just returns the node. This will typically suffice as the default visit operation for most visitors unless the visitor needs to count the number of nodes visited or something like that.

Visitors will overload this method by implementing a version with a signature that matches a specific type of node. For example, if I want to do something special with aggregate nodes, then that Visitor will implement a visit(AggregateNode node) method which does the aggregate specific processing.

Specified by:

visit in interface Visitor

Parameters:

node - the node to process

Returns:

a query tree node. Often times this is the same node that was passed in, but Visitors that replace nodes with other nodes will use this to return the new replacement node.

Throws:

StandardException - may be throw an error as needed by the visitor (i.e. may be a normal error if a particular node is found, e.g. if checking a group by, we don't expect to find any ColumnReferences that aren't under an AggregateNode -- the easiest thing to do is just throw an error when we find the questionable node).

stopTraversal

public boolean stopTraversal()

Description copied from interface: Visitor

Method that is called to see if query tree traversal should be stopped before visiting all nodes. Useful for short circuiting traversal if we already know we are done.

Specified by:

stopTraversal in interface Visitor

Returns:

true/false

skipChildren

public boolean skipChildren(Visitable node)

Description copied from interface: Visitor

Method that is called to indicate whether we should skip all nodes below this node for traversal. Useful if we want to effectively ignore/prune all branches under a particular node.

Differs from stopTraversal() in that it only affects subtrees, rather than the entire traversal.

Specified by:

skipChildren in interface Visitor

Parameters:

node - the node to process

Returns:

true/false

visitChildrenFirst

public boolean visitChildrenFirst(Visitable node)

Description copied from interface: Visitor

Method that is called to see if visit() should be called on the children of node before it is called on node itself. If this method always returns true, the visitor will walk the tree bottom-up. If it always returns false, the tree is visited top-down.

Specified by:

visitChildrenFirst in interface Visitor

Parameters:

node - the top node of a sub-tree about to be visited

Returns:

true if node's children should be visited before node, false otherwise