net.esper.view.std
Class GroupByView

java.lang.Object
  extended by net.esper.view.ViewSupport
      extended by net.esper.view.std.GroupByView
All Implemented Interfaces:
Iterable<EventBean>, CloneableView, EventCollection, View, Viewable

public final class GroupByView
extends ViewSupport
implements CloneableView

The group view splits the data in a stream to multiple subviews, based on a key index. The key is one or more fields in the stream. Any view that follows the GROUP view will be executed separately on each subview, one per unique key. The view takes a single parameter which is the field name returning the key value to group. This view can, for example, be used to calculate the average price per symbol for a list of symbols. The view treats its child views and their child views as prototypes. It dynamically instantiates copies of each child view and their child views, and the child view's child views as so on. When there are no more child views or the special merge view is encountered, it ends. The view installs a special merge view unto each leaf child view that merges the value key that was grouped by back into the stream using the group-by field name.


Field Summary
 
Fields inherited from class net.esper.view.ViewSupport
parent
 
Constructor Summary
GroupByView(StatementContext statementContext, String[] groupFieldNames)
          Constructor.
 
Method Summary
 View cloneView(StatementContext statementContext)
          Duplicates the view.
 EventType getEventType()
          Provides metadata information about the type of object the event collection contains.
 String[] getGroupFieldNames()
          Returns the field name that provides the key valie by which to group by.
 Iterator<EventBean> iterator()
          Allows iteration through all elements in this event collection.
protected static List<View> makeSubViews(GroupByView groupView, Object[] groupByValues, StatementContext statementContext)
          Instantiate subviews for the given group view and the given key value to group-by.
 void setParent(Viewable parent)
          Called when the View is added to a Viewable object.
 String toString()
           
 void update(EventBean[] newData, EventBean[] oldData)
          Notify that data has been added or removed from the Viewable parent.
 
Methods inherited from class net.esper.view.ViewSupport
addView, dumpChildViews, dumpUpdateParams, findDescendent, getParent, getViews, hasViews, removeView, updateChildren, updateChildren
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
 

Constructor Detail

GroupByView

public GroupByView(StatementContext statementContext,
                   String[] groupFieldNames)
Constructor.

Parameters:
groupFieldNames - is the fields from which to pull the values to group by
statementContext - contains required view services
Method Detail

cloneView

public View cloneView(StatementContext statementContext)
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
Parameters:
statementContext - is services for the view
Returns:
duplicated view

setParent

public void setParent(Viewable parent)
Description copied from interface: View
Called when the View is added to a Viewable object.

Specified by:
setParent in interface View
Overrides:
setParent in class ViewSupport
Parameters:
parent - is the parent that this view is a child of

getGroupFieldNames

public String[] getGroupFieldNames()
Returns the field name that provides the key valie by which to group by.

Returns:
field name providing group-by key.

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

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 Iterable<EventBean>
Specified by:
iterator in interface EventCollection
Returns:
an iterator which will go through all current elements in the collection.

toString

public final String toString()
Overrides:
toString in class Object

makeSubViews

protected static List<View> makeSubViews(GroupByView groupView,
                                         Object[] groupByValues,
                                         StatementContext statementContext)
Instantiate subviews for the given group view and the given key value to group-by. Makes shallow copies of each child view and its subviews up to the merge point. Sets up merge data views for merging the group-by key value back in.

Parameters:
groupView - is the parent view for which to copy subviews for
groupByValues - is the key values to group-by
statementContext - is the view services that sub-views may need
Returns:
a list of views that are copies of the original list, with copied children, with data merge views added to the copied child leaf views.