com.espertech.esper.common.client.hook.aggmultifunc

Interface AggregationMultiFunctionHandler

public interface AggregationMultiFunctionHandler

Part of the aggregation multi-function extension API, this class represents one of more aggregation function expression instances. This class is responsible for providing a state reader (called accessor) for returning value from aggregation state, and for providing return type information of the accessor, and for providing state factory information.

Note the information returned by getReturnType() must match the value objects returned by accessors provided by getAccessorMode().

For example, assuming you have an EPL statement such as select search(), query() from MyEvent then you would likely use one handler class and two handler objects (one for search and one for query).

Method Summary

Modifier and Type	Method and Description
AggregationMultiFunctionAccessorMode	getAccessorMode() Describes to the compiler how it should manage code for providing aggregation accessors.
AggregationMultiFunctionAgentMode	getAgentMode() Describes to the compiler how it should manage code for providing aggregation agents.
AggregationMultiFunctionStateKey	getAggregationStateUniqueKey() Return a state-key object that determines how the runtimeshares aggregation state between multiple aggregation functions that may appear in the same EPL statement.
EPType	getReturnType() Provide return type.
AggregationMultiFunctionStateMode	getStateMode() Describes to the compiler how it should manage code for providing aggregation state.
AggregationMultiFunctionTableReaderMode	getTableReaderMode() Describes to the compiler how it should manage code for providing table column reader.

Method Detail

getReturnType

EPType getReturnType()

Provide return type.

The accessor return values must match the return type declared herein.

Use EPTypeHelper.singleValue(Class) (Class)} to indicate that the accessor returns a single value. The accessor should return the single value upon invocation of AggregationMultiFunctionAccessor.getValue(AggregationMultiFunctionState, EventBean[], boolean, ExprEvaluatorContext). The accessor should return a null value for all other accessor methods.

Use EPTypeHelper.collectionOfEvents(EventType) to indicate that the accessor returns a collection of events. The accessor should return a value in AggregationMultiFunctionAccessor.getEnumerableEvents(AggregationMultiFunctionState, EventBean[], boolean, ExprEvaluatorContext). The accessor can also return an array of underlying event objects in AggregationMultiFunctionAccessor.getValue(AggregationMultiFunctionState, EventBean[], boolean, ExprEvaluatorContext). The accessor should return a null value for all other accessor methods.

Use EPTypeHelper.singleEvent(EventType) to indicate that the accessor returns a single event. The accessor should return a value in AggregationMultiFunctionAccessor.getEnumerableEvent(AggregationMultiFunctionState, EventBean[], boolean, ExprEvaluatorContext). The accessor can also return the underlying event object in AggregationMultiFunctionAccessor.getValue(AggregationMultiFunctionState, EventBean[], boolean, ExprEvaluatorContext). The accessor should return a null value for all other accessor methods.

Use EPTypeHelper.collectionOfSingleValue(Class) to indicate that the accessor returns a collection of single values (scalar, object etc.). The accessor should return a java.util.Collection in AggregationMultiFunctionAccessor.getValue(AggregationMultiFunctionState, EventBean[], boolean, ExprEvaluatorContext). The accessor should return a null value for all other accessor methods.

Use EPTypeHelper.array(Class) to indicate that the accessor returns an array of single values. The accessor should return an array in AggregationMultiFunctionAccessor.getValue(AggregationMultiFunctionState, EventBean[], boolean, ExprEvaluatorContext). The accessor should return a null value for all other accessor methods.

Returns:

expression result type

getAggregationStateUniqueKey

AggregationMultiFunctionStateKey getAggregationStateUniqueKey()

Return a state-key object that determines how the runtimeshares aggregation state between multiple aggregation functions that may appear in the same EPL statement.

The runtimeapplies equals-semantics to determine state sharing. If two AggregationMultiFunctionStateKey instances are equal (implement hashCode and equals) then the runtimeshares a single aggregation state instance for the two aggregation function expressions.

If your aggregation function never needs shared state simple return new AggregationStateKey(){}.

If your aggregation function always shares state simple declare private static final AggregationStateKey MY_KEY = new AggregationStateKey() {}; and return MY_KEY; (if using multiple handlers declare the key on the factory level).

Returns:

state key

getStateMode

AggregationMultiFunctionStateMode getStateMode()

Describes to the compiler how it should manage code for providing aggregation state.

Returns:

mode object

getAccessorMode

AggregationMultiFunctionAccessorMode getAccessorMode()

Describes to the compiler how it should manage code for providing aggregation accessors.

Returns:

mode object

getAgentMode

AggregationMultiFunctionAgentMode getAgentMode()

Describes to the compiler how it should manage code for providing aggregation agents.

Returns:

mode object

getTableReaderMode

AggregationMultiFunctionTableReaderMode getTableReaderMode()

Describes to the compiler how it should manage code for providing table column reader.

Returns:

mode object