org.mmbase.module.core
Class ClusterNode

java.lang.Object
  org.mmbase.module.core.MMObjectNode
      org.mmbase.module.core.VirtualNode
          org.mmbase.module.core.ClusterNode

All Implemented Interfaces:

SizeMeasurable

public class ClusterNode

extends VirtualNode

ClusterNode combines fields of different nodes in a single "virtual" node.
This corresponds to the way that an SQL "join" select statement combines fields of different tables in result rows.

The individual fields are retrieved from a set of related nodes using a multilevel query, i.e. a query joining tables using the relations between the tables.

This class overrides a number of methods, allowing direct access to data in the nodes which form the 'virtual' node.
In future releases, data will NOT be stored directkly in this node anymore. Instead, it will be stored in the underlying MMObjectNodes. For reasons of optiomalization, however, we cannot do this right now. MMObjectNode will need a status field that allows us to recognize whether it is fully loaded, partially loaded, or being edited. This can then be checked in 'retrievevalue'. In addition, to prevent caching conflicts, nodes will need to maintain their references. This allows for a secure caching mechanism.
Among other things, this allows one to change values in a multilevel node, or to access functionality that would otherwise be restricted to 'real' nodes.

Version:

$Id: ClusterNode.java,v 1.14.2.1 2004/06/18 12:37:22 michiel Exp $

Author:

Pierre van Rooden

See Also:

ClusterBuilder

Field Summary

protected java.util.Hashtable

nodes Holds the name - value pairs of related nodes in this virtual node.

Fields inherited from class org.mmbase.module.core.MMObjectNode

alias, changed, initializing, parent, prefix, properties, relatedCache, relationsCache, VALUE_NULL, values, virtual

Constructor Summary

ClusterNode(MMObjectBuilder parent)
Main contructor.

ClusterNode(MMObjectBuilder parent, int nrofnodes)
Main contructor.

Method Summary

boolean	commit() commit : commits the node to the database or other storage system.
MMObjectBuilder	getBuilder() Returns the actual builder of the node.
protected java.lang.String	getBuilderName(java.lang.String fieldName) Determines the builder name of a specified fieldname, i.e.
byte[]	getByteValue(java.lang.String fieldName) Get a binary value of a certain field.
MMObjectNode	getRealNode(java.lang.String builderName) Obtain the 'real' nodes, associated with a specified objectbuilder.
java.util.Enumeration	getRelations() Return the relations of this node.
java.lang.String	getStringValue(java.lang.String fieldName) Get a value of a certain field.
java.lang.Object	getValue(java.lang.String fieldName) Get a value of a certain field.
boolean	isChanged() Tests whether one of the values of this node was changed since the last commit/insert.
boolean	setValue(java.lang.String fieldName, java.lang.Object fieldValue) Sets a key/value pair in the main values of this node.
void	storeValue(java.lang.String fieldName, java.lang.Object fieldValue) Stores a value in the values hashtable.
void	testValidData() Tests whether the data in a node is valid (throws an exception if this is not the case).

Methods inherited from class org.mmbase.module.core.VirtualNode

getAge, getRelationCount, getRelationCount, hasRelations, insert

Methods inherited from class org.mmbase.module.core.MMObjectNode

clearChanged, commit, defaultEquals, delPropertiesCache, delRelationsCache, equals, finish, getAlias, getAllRelations, getBooleanValue, getByteSize, getByteSize, getChanged, getContext, getDBState, getDBType, getDoubleValue, getFloatValue, getFunctionValue, getGUIIndicator, getIntegerValue, getIntValue, getLongValue, getName, getNodeValue, getNumber, getOType, getPossibleContexts, getProperties, getProperty, getRelatedNodes, getRelatedNodes, getRelatedNodes, getRelatedNodes, getRelationCacheHits, getRelationCacheMiss, getRelationNodes, getRelations, getRelations, getTableName, getValues, getXMLValue, hashCode, insert, insertDone, isVirtual, preEdit, putProperty, remove, removeRelations, retrieveValue, sendFieldChangeSignal, setAlias, setContext, setValue, setValue, setValue, setValue, setValue, start, toString, toXML, toXML

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Field Detail

nodes

protected java.util.Hashtable nodes

Holds the name - value pairs of related nodes in this virtual node.

Constructor Detail

ClusterNode

public ClusterNode(MMObjectBuilder parent)

Main contructor.

Parameters:

parent - the node's parent, generally an instance of the ClusterBuilder builder.

ClusterNode

public ClusterNode(MMObjectBuilder parent,
                   int nrofnodes)

Main contructor.

Parameters:

parent - the node's parent, generally an instance of the ClusterBuilder builder.

Method Detail

testValidData

public void testValidData()
                   throws InvalidDataException

Tests whether the data in a node is valid (throws an exception if this is not the case). The call is performed on all loaded 'real' nodes. If a 'real' node has not previously been forcably loaded, it is assumed to be correct.

Overrides:

testValidData in class MMObjectNode

Throws:

InvalidDataException - If the data was unrecoverably invalid (the references did not point to existing objects)

commit

public boolean commit()

commit : commits the node to the database or other storage system. This can only be done on a existing (inserted) node. it will use the changed Vector as its base of what to commit/changed

Overrides:

commit in class VirtualNode

Returns:

true if the commit was succesfull, false is it failed

getRealNode

public MMObjectNode getRealNode(java.lang.String builderName)

Obtain the 'real' nodes, associated with a specified objectbuilder.

Returns:

the node, or null if it does not exist or is unknown

storeValue

public void storeValue(java.lang.String fieldName,
                       java.lang.Object fieldValue)

Stores a value in the values hashtable. If the value is not stored in the virtualnode, the 'real' node is used instead.

Overrides:

storeValue in class MMObjectNode

Parameters:

fieldValue - the value to assign

fieldName - the name of the field to change

setValue

public boolean setValue(java.lang.String fieldName,
                        java.lang.Object fieldValue)

Sets a key/value pair in the main values of this node. Note that if this node is a node in cache, the changes are immediately visible to everyone, even if the changes are not committed. The fieldname is added to the (public) 'changed' vector to track changes.

Overrides:

setValue in class MMObjectNode

Parameters:

fieldValue - the value to assign

fieldName - the name of the field to change

Returns:

always true

getBuilderName

protected java.lang.String getBuilderName(java.lang.String fieldName)

Determines the builder name of a specified fieldname, i.e. "news" in "news.title",

Returns:

the buidler name of the field

getBuilder

public MMObjectBuilder getBuilder()

Description copied from class: MMObjectNode

Returns the actual builder of the node. Note that it is possible that, due to optimization, a node is currently associated with another (parent) builder, i.e. a posrel node may be associated with a insrel builder. This method returns the actual builder. The node may miss vital information (not retrieved from the database) to act as a node of such a builder - if you need actual status you need to reload it.

Overrides:

getBuilder in class MMObjectNode

Returns:

the builder of this node

getValue

public java.lang.Object getValue(java.lang.String fieldName)

Get a value of a certain field.

Overrides:

getValue in class MMObjectNode

Parameters:

fieldName - the name of the field who's data to return

Returns:

the field's value as an Object

getStringValue

public java.lang.String getStringValue(java.lang.String fieldName)

Get a value of a certain field. The value is returned as a String. Non-string values are automatically converted to String.

Overrides:

getStringValue in class MMObjectNode

Parameters:

fieldName - the name of the field who's data to return

Returns:

the field's value as a String

getByteValue

public byte[] getByteValue(java.lang.String fieldName)

Get a binary value of a certain field.

Overrides:

getByteValue in class MMObjectNode

Parameters:

fieldName - the name of the field who's data to return

Returns:

the field's value as an byte [] (binary/blob field)

isChanged

public boolean isChanged()

Tests whether one of the values of this node was changed since the last commit/insert.

Overrides:

isChanged in class MMObjectNode

Returns:

true if changes have been made, false otherwise

getRelations

public java.util.Enumeration getRelations()

Return the relations of this node. This is not allowed on a cluster node

Overrides:

getRelations in class VirtualNode

Returns:

empty Enumeration

Throws:

RuntimeException