MergeView.java

/**************************************************************************************
 * Copyright (C) 2008 EsperTech, Inc. All rights reserved.                            *
 * http://esper.codehaus.org                                                          *
 * http://www.espertech.com                                                           *
 * ---------------------------------------------------------------------------------- *
 * The software in this package is published under the terms of the GPL license       *
 * a copy of which has been included with this distribution in the license.txt file.  *
 **************************************************************************************/
package com.espertech.esper.view.std;

import com.espertech.esper.client.EventBean;
import com.espertech.esper.client.EventType;
import com.espertech.esper.collection.IterablesListIterator;
import com.espertech.esper.core.context.util.AgentInstanceViewFactoryChainContext;
import com.espertech.esper.epl.expression.ExprNode;
import com.espertech.esper.view.CloneableView;
import com.espertech.esper.view.View;
import com.espertech.esper.view.ViewSupport;
import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import java.util.ArrayDeque;
import java.util.Arrays;
import java.util.Iterator;

/**
 * The merge view works together with a group view that splits the data in a stream to multiple subviews, based on
 * a key index. Every group view requires a merge view to merge the many subviews back into a single view.
 * Typically the last view in a chain containing a group view is a merge view.
 * The merge view has no other responsibility then becoming the single last instance in the chain
 * to which external listeners for updates can be attached to receive updates for the many subviews
 * that have this merge view as common child views.
 * The parent view of this view is generally the AddPropertyValueView that adds the grouped-by information
 * back into the data.
 */
public final class MergeView extends ViewSupport implements CloneableView, MergeViewMarker
{
    private final AgentInstanceViewFactoryChainContext agentInstanceContext;
    private final ArrayDeque<View> parentViews = new ArrayDeque<View>();
    private final ExprNode[] groupFieldNames;
    private final EventType eventType;

    /**
     * Constructor.
     * @param groupCriteria is the fields from which to pull the value to group by
     * @param resultEventType is passed by the factory as the factory adds the merged fields to an event type
     */
    public MergeView(AgentInstanceViewFactoryChainContext agentInstanceContext, ExprNode[] groupCriteria, EventType resultEventType)
    {
        this.agentInstanceContext = agentInstanceContext;
        this.groupFieldNames = groupCriteria;
        this.eventType = resultEventType;
    }

    public View cloneView()
    {
        return new MergeView(agentInstanceContext, groupFieldNames, eventType);
    }

    /**
     * Returns the field name that contains the values to group by.
     * @return field name providing group key value
     */
    public final ExprNode[] getGroupFieldNames()
    {
        return groupFieldNames;
    }

    /**
     * Add a parent data merge view.
     * @param parentView is the parent data merge view to add
     */
    public final void addParentView(AddPropertyValueView parentView)
    {
        parentViews.add(parentView);
    }

    public final EventType getEventType()
    {
        // The schema is the parent view's type, or the type plus the added field(s)
        return eventType;
    }

    public final void update(EventBean[] newData, EventBean[] oldData)
    {
        updateChildren(newData, oldData);
    }

    public final Iterator<EventBean> iterator()
    {
        // The merge data view has multiple parent views which are AddPropertyValueView
        ArrayDeque<Iterable<EventBean>> iterables = new ArrayDeque<Iterable<EventBean>>();

        for (View dataView : parentViews)
        {
            iterables.add(dataView);
        }

        return new IterablesListIterator(iterables);
    }

    public final String toString()
    {
        return this.getClass().getName() + " groupFieldName=" + Arrays.toString(groupFieldNames);
    }

    public void removeParentView(View view)
    {
        parentViews.remove(view);
    }

    private static final Log log = LogFactory.getLog(MergeView.class);
}