parent-child-relationship.markdown

type	post
title	Parent Child Relationship
categories	SBP
parent	modeling-your-data.html
weight	100

{{% ssummary %}}Constructing Parent-Child Relationships with GigaSpaces Data-Grid{{% /ssummary %}}

Parent-Child Relationship

In some cases, you might want to store objects within the space that include references to other space objects -- i.e. an object graph. With such object relationships, you might want to fetch a parent object that is associated with a child object(s) holds a specific data (join).

{{% tip %}} See the Modeling your data section for details about when you should construct strong relationship between parent-child objects (embed) and when you should not embed child objects within their parent but have the ID of child objects placed within the parent object. {{% /tip %}}

The example below demonstrates how ID operations handle relationships between objects. This example using the readByIds batch operation to retrieve multiple space objects using on their ID:

ReadByIdsResult<Child> childrenObjResult = space.readByIds(Child.class,childrenIDs);

The example writes 10000 parent-child graphs into the space. Two types of graphs will be created with this example:

• 5 graphs with the following values for the child objects: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9.
• 9955 graphs with the following values for the child objects: 0, 10, 20, 30, 40, 50, 60, 70, 80, 90.

The example demonstrates a simple approach locating all the parent objects that have two child objects with values of 1 and 2 -- effectively a join operation using ID operations. This will return 5 matching graphs.

{{% tip %}} The full example source code can be downloaded here. {{% /tip %}}

{{%tabs%}} {{%tab " Child Class "%}}

package com.j_spaces.examples.parentchild;

import com.gigaspaces.annotation.pojo.SpaceClass;
import com.gigaspaces.annotation.pojo.SpaceId;
import com.gigaspaces.annotation.pojo.SpaceIndex;
import com.gigaspaces.annotation.pojo.SpaceRouting;
import com.gigaspaces.metadata.index.SpaceIndexType;
;

@SpaceClass
public class Child {

	private String parentID;
	private Long data;
	private String id;

	public Child(){}

	public Child(String id, String _parentID)
	{
		this.parentID = _parentID;
		this.id = id;
	}

	public String toString()
	{
		return "ID:" + id + " data:" + data;
	}

	@SpaceIndex(type=SpaceIndexType.BASIC)
	public Long getData() {
		return data;
	}

	public void setData(Long data) {
		this.data= data;
	}

	@SpaceId (autoGenerate = false)
	public String getId() {
		return id;
	}

	public void setId(String id) {
		this.id = id;
	}

	@SpaceIndex(type=SpaceIndexType.BASIC)
	@SpaceRouting
	public String getParentID() {
		return parentID;
	}

	public void setParentID(String parentID) {
		this.parentID = parentID;
	}
}

{{%/tab%}}

{{%tab " Parent class "%}}

package com.j_spaces.examples.parentchild;

import java.rmi.RemoteException;

import org.openspaces.core.GigaSpace;

import net.jini.core.entry.UnusableEntryException;
import net.jini.core.transaction.TransactionException;

import com.gigaspaces.annotation.pojo.SpaceClass;
import com.gigaspaces.annotation.pojo.SpaceId;
import com.gigaspaces.annotation.pojo.SpaceIndex;
import com.gigaspaces.annotation.pojo.SpaceRouting;
import com.gigaspaces.client.ReadByIdsResult;
import com.gigaspaces.metadata.index.SpaceIndexType;

@SpaceClass
public class Parent  {

	private String childrenIDs[];
	private transient Child children[];
	private Long data;
	private String id;

	static final String ChildClassName = Child.class.getName();

	public Parent() {
	}

	public Parent(String id) {
		this.id = id;
	}

	public String _getChildrenDetails(GigaSpace space) throws
		RemoteException,
		TransactionException,
		UnusableEntryException
	{
		String ret="";
		Child[] childs = _getChildren(space);
		for (int i=0;i<childs.length ; i++)
		{
			ret = ret + childs[i].toString() + " | ";
		}
		return ret;

	}

	public Child[] _getChildren(GigaSpace space) throws
		RemoteException,
		TransactionException,
		UnusableEntryException
	{
		if (children == null)
		{
			ReadByIdsResult<Child> childrenObjResult = space.readByIds(Child.class,childrenIDs);
			children = childrenObjResult.getResultsArray();
		}
		return children;
	}

	public String _getChildrenIDs()
	{
		String res ="";
		for (int i=0 ; i< childrenIDs.length; i++)
		{
			res =res +childrenIDs[i] + "\n";
		}
		return res;
	}

	@SpaceIndex(type=SpaceIndexType.BASIC)
	public Long getData() {
		return data;
	}

	public void setData(Long data) {
		this.data = data;
	}

	public String[] getChildrenIDs() {
		return childrenIDs;
	}

	public void setChildrenIDs(String[] _childrenIDs ) {
		this.childrenIDs = _childrenIDs ;
	}

	@SpaceId(autoGenerate=false)
	@SpaceRouting
	public String getId() {
		return id;
	}

	public void setId(String id) {
		this.id = id;
	}

}

{{%/tab%}}

{{%tab " Application "%}}

package com.j_spaces.examples.parentchild;

import java.rmi.RemoteException;
import java.util.HashSet;
import java.util.Set;

import org.openspaces.core.GigaSpace;
import org.openspaces.core.GigaSpaceConfigurer;
import org.openspaces.core.space.UrlSpaceConfigurer;
import net.jini.core.entry.UnusableEntryException;
import net.jini.core.transaction.TransactionException;
import com.gigaspaces.client.ReadByIdsResult;

public class ParentChildMain {

	static GigaSpace space;
	static int max_graphs = 10000;
	static int matching_graphs = 5;

	public static void main(String[] args) {
		try {

			 UrlSpaceConfigurer urlSpaceConfigurer = new UrlSpaceConfigurer("/./mySpace");
			 space = new GigaSpaceConfigurer(urlSpaceConfigurer.space()).gigaSpace();

			System.out.println("Write " + max_graphs+ " parent/child graphs.\nWe will have 2 types of graphs:" +
					"\n" +  matching_graphs+
						" graphs that got the following values for the child objects:0,1,2,3,4,5,6,7,8,9" +
					"\nand another "  +(max_graphs - matching_graphs) +
						" graphs with the following values for the child objects:0,10,20,30,40,50,60,70,80,90");

			go();

		} catch (Exception e) {
			e.printStackTrace();
		}		}

		static public void go() throws Exception
		{
			for (int i = 0; i < max_graphs; i++) {
				Parent parent = new Parent(i +"");
				Child _children[] = new Child[10];
				String _childrenIDs[] = new String[10];
				for (int j = 0; j < 10; j++) {
					_children[j] = new Child(i + "_" + j,parent.getId());
					if (i% (max_graphs/matching_graphs) ==0)
						_children[j].setData(new Long(j));
					else
						_children[j].setData (new Long(j * 10));

					_childrenIDs[j] = _children[j].getId();
				}
				parent.setChildrenIDs (_childrenIDs);

				space.write(parent);
				space.writeMultiple(_children);
			}

			findMatchingGraph(1,2);
			findMatchingGraph(3,4);
			findMatchingGraph(5,6);
			findMatchingGraph(7,8);
	}

	static void findMatchingGraph(long value1, long value2) throws Exception
	{
		System.out.println("-----------------------------------------------------------------");
		System.out.println("Find all the parent objects that got 2 child objects with values " +
			value1 +" and " + value2+ "");
		System.out.println("Both child objects have the same parent object");
		Long startTime = System.nanoTime();
		Object childrenResults1[] = findChildrenByValue(new Long(value1));
		Set<String> parentIDs1 = getParentIDsSet(childrenResults1);

		Object childrenResults2[] = findChildrenByValue(new Long(value2));
		Set<String> parentIDs2 = getParentIDsSet(childrenResults2);

		Set<String> resultSet = AND(parentIDs1, parentIDs2);

		Parent parents[] = getParentsfromIDs(resultSet);
		Long endTime = System.nanoTime();
		System.out.println(" --->> Found " + parents.length +
			" matching Parent objects in " + (double)(((double)endTime - (double)startTime)/1000) + " micro second");

		for (int i = 0; i < parents.length; i++) {
			System.out.println("Found Parent Object:" + parents[i]
					+ " - ID:" + parents[i].getId() + " - His children objects are:\n\t"
					+ parents[i]._getChildrenDetails(space));
		}

	}

	static public Object[] findChildrenByValue(Long value) throws
		RemoteException,
		TransactionException,
		UnusableEntryException {
		Child childTemplate = new Child();
		childTemplate.setData(value);
		return space.readMultiple(childTemplate , Integer.MAX_VALUE);
	}

	static public Set<String> getParentIDsSet(Object entries[]) {
		HashSet<String> result = new HashSet<String>();
		for (int i = 0; i < entries.length; i++) {
			result.add(((Child) entries[i]).getParentID());
		}
		return result;
	}

	static public Parent[] getParentsfromIDs(Set ids) throws
		UnusableEntryException,
		RemoteException,
		TransactionException
	{
		ReadByIdsResult<Parent> parentObjResult = space.readByIds(Parent.class,ids.toArray());
		return parentObjResult.getResultsArray();
	}

	// find union between set1 and set2
	static public Set<String> AND(Set<String> set1, Set<String> set2) {
		HashSet<String> result = new HashSet<String>(set1);
		result.retainAll(set2);
		return result;
	}
}

{{%/tab%}}

{{%/tabs%}}

Expected output

Write 10000 parent/child graphs.
We will have 2 types of graphs:
5 graphs that got the following values for the child objects:0,1,2,3,4,5,6,7,8,9
and another 9995 graphs with the following values for the child objects:0,10,20,30,40,50,60,70,80,90
-----------------------------------------------------------------
Find all the parent objects that got 2 child objects with values 1 and 2
Both child objects have the same parent object
 --->> Found 5 matching Parent objects in 623.38 micro second
Found Parent Object:com.j_spaces.examples.parentchild.Parent@335053 - ID:8000 - His children objects are:
	ID:8000_0 data:0 | ID:8000_1 data:1 | ID:8000_2 data:2 | ....
Found Parent Object:com.j_spaces.examples.parentchild.Parent@1c0cd80 - ID:0 - His children objects are:
	ID:0_0 data:0 | ID:0_1 data:1 | ID:0_2 data:2 | ...
Found Parent Object:com.j_spaces.examples.parentchild.Parent@f3c5c4 - ID:6000 - His children objects are:
	ID:6000_0 data:0 | ID:6000_1 data:1 | ID:6000_2 data:2 | ...
Found Parent Object:com.j_spaces.examples.parentchild.Parent@3ce725 - ID:4000 - His children objects are:
	ID:4000_0 data:0 | ID:4000_1 data:1 | ID:4000_2 data:2 | ...
Found Parent Object:com.j_spaces.examples.parentchild.Parent@6b6ac8 - ID:2000 - His children objects are:
	ID:2000_0 data:0 | ID:2000_1 data:1 | ID:2000_2 data:2 | ...