com.espertech.esper.view.std

Class UniqueByPropertyView

java.lang.Object

com.espertech.esper.view.ViewSupport

com.espertech.esper.view.std.UniqueByPropertyView

All Implemented Interfaces:

CloneableView, DataWindowView, EventCollection, GroupableView, View, Viewable, ViewDataVisitable, Iterable<EventBean>

public class UniqueByPropertyView
extends ViewSupport
implements CloneableView, DataWindowView

This view includes only the most recent among events having the same value for the specified field or fields. The view accepts the field name as parameter from which the unique values are obtained. For example, a trade's symbol could be used as a unique value. In this example, the first trade for symbol IBM would be posted as new data to child views. When the second trade for symbol IBM arrives the second trade is posted as new data to child views, and the first trade is posted as old data. Should more than one trades for symbol IBM arrive at the same time (like when batched) then the child view will get all new events in newData and all new events in oldData minus the most recent event. When the current new event arrives as old data, the the current unique event gets thrown away and posted as old data to child views. Iteration through the views data shows only the most recent events received for the unique value in the order that events arrived in. The type of the field returning the unique value can be any type but should override equals and hashCode() as the type plays the role of a key in a map storing unique values.

Field Summary

Fields

Modifier and Type	Field and Description
protected AgentInstanceViewFactoryChainContext	agentInstanceViewFactoryContext
protected Map<Object,EventBean>	mostRecentEvents

Fields inherited from class com.espertech.esper.view.ViewSupport

EMPTY_VIEW_ARRAY, parent

Constructor Summary

Constructors

Constructor and Description
UniqueByPropertyView(UniqueByPropertyViewFactory viewFactory, AgentInstanceViewFactoryChainContext agentInstanceViewFactoryContext)

Method Summary

Modifier and Type	Method and Description
View	cloneView() Duplicates the view.
ExprNode[]	getCriteriaExpressions() Returns the name of the field supplying the unique value to keep the most recent record for.
EventType	getEventType() Provides metadata information about the type of object the event collection contains.
protected Object	getUniqueKey(EventBean theEvent)
ViewFactory	getViewFactory()
boolean	isEmpty() Returns true if the view is empty.
Iterator<EventBean>	iterator() Allows iteration through all elements in this event collection.
String	toString()
void	update(EventBean[] newData, EventBean[] oldData) Notify that data has been added or removed from the Viewable parent.
void	visitView(ViewDataVisitor viewDataVisitor)

Methods inherited from class com.espertech.esper.view.ViewSupport

addView, addView, dumpChildViews, dumpUpdateParams, dumpUpdateParams, findDescendent, findViewIndex, getParent, getViews, hasViews, removeAllViews, removeView, removeView, setParent, updateChildren, updateChildren

Methods inherited from class java.lang.Object

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

Methods inherited from interface com.espertech.esper.view.View

getParent, setParent

Methods inherited from interface com.espertech.esper.view.Viewable

addView, getViews, hasViews, removeAllViews, removeView

Methods inherited from interface java.lang.Iterable

forEach, spliterator

Field Detail

mostRecentEvents

protected final Map<Object,EventBean> mostRecentEvents

agentInstanceViewFactoryContext

protected final AgentInstanceViewFactoryChainContext agentInstanceViewFactoryContext

Constructor Detail

UniqueByPropertyView

public UniqueByPropertyView(UniqueByPropertyViewFactory viewFactory,
                            AgentInstanceViewFactoryChainContext agentInstanceViewFactoryContext)

Method Detail

cloneView

public View cloneView()

Description copied from interface: CloneableView

Duplicates the view.

Expected to return a same view in initialized state for grouping.

Specified by:

cloneView in interface CloneableView

Returns:

cloned view

getCriteriaExpressions

public final ExprNode[] getCriteriaExpressions()

Returns the name of the field supplying the unique value to keep the most recent record for.

Returns:

expressions for unique value

getEventType

public final EventType getEventType()

Description copied from interface: EventCollection

Provides metadata information about the type of object the event collection contains.

Specified by:

getEventType in interface EventCollection

Returns:

metadata for the objects in the collection

update

public final void update(EventBean[] newData,
                         EventBean[] oldData)

Description copied from interface: View

Notify that data has been added or removed from the Viewable parent. The last object in the newData array of objects would be the newest object added to the parent view. The first object of the oldData array of objects would be the oldest object removed from the parent view.

If the call to update contains new (inserted) data, then the first argument will be a non-empty list and the second will be empty. Similarly, if the call is a notification of deleted data, then the first argument will be empty and the second will be non-empty. Either the newData or oldData will be non-null. This method won't be called with both arguments being null, but either one could be null. The same is true for zero-length arrays. Either newData or oldData will be non-empty. If both are non-empty, then the update is a modification notification.

When update() is called on a view by the parent object, the data in newData will be in the collection of the parent, and its data structures will be arranged to reflect that. The data in oldData will not be in the parent's data structures, and any access to the parent will indicate that that data is no longer there.

Specified by:

update in interface View

Parameters:

newData - is the new data that has been added to the parent view

oldData - is the old data that has been removed from the parent view

isEmpty

public boolean isEmpty()

Returns true if the view is empty.

Returns:

true if empty

iterator

public final Iterator<EventBean> iterator()

Description copied from interface: EventCollection

Allows iteration through all elements in this event collection. The iterator will return the elements in the collection in their natural order, or, if there is no natural ordering, in some unpredictable order.

Specified by:

iterator in interface EventCollection

Specified by:

iterator in interface Iterable<EventBean>

Returns:

an iterator which will go through all current elements in the collection.

toString

public final String toString()

Overrides:

toString in class Object

getUniqueKey

protected Object getUniqueKey(EventBean theEvent)

visitView

public void visitView(ViewDataVisitor viewDataVisitor)

Specified by:

visitView in interface ViewDataVisitable

getViewFactory

public ViewFactory getViewFactory()

Specified by:

getViewFactory in interface GroupableView