public interface PlugInAggregationMultiFunctionFactory extends Serializable
This API allows adding one or more related aggregation functions that can share state, share parameters or exhibit related behavior.
Please use ConfigurationPlugInAggregationMultiFunction
to register this factory class in the engine together with one or more function names.
The engine instantiates a single instance of this class at the time it encounters the first aggregation multi-function in a given statement at the time of statement parsing or compilation from statement object model.
At the time of statement parsing, each aggregation multi-function encountered during parsing
of EPL statement text results in an invocation to addAggregationFunction(PlugInAggregationMultiFunctionDeclarationContext). The same
upon statement compilation for statement object model.
For multiple aggregation functions, the order in which such calls occur is not well defined
and should not be relied on by the implementation.
The engine invokes validateGetHandler(PlugInAggregationMultiFunctionValidationContext)
at the time of expression node validation. Validation occurs after statement parsing
and when type information is established.
For multiple aggregation functions, the order in which such calls occur is not well defined
and should not be relied on by the implementation.
Usually a single PlugInAggregationMultiFunctionHandler handler class can handle the needs
of all related aggregation functions.
Usually you have a single handler class and return one handler object for each
aggregation function expression, where the handler object takes the validation context as a parameter.
Use multiple different handler classes when your aggregation
functions have sufficiently different execution contexts or behaviors. Your application may want to use the
expression and type information available in
PlugInAggregationMultiFunctionValidationContext to decide what behavior to provide.
The function class must be Serializable only when used with EsperHA.
| Modifier and Type | Method and Description |
|---|---|
void |
addAggregationFunction(PlugInAggregationMultiFunctionDeclarationContext declarationContext)
Called for each instance of use of any of the aggregation functions at declaration discovery time
and before any expression validation takes place.
|
PlugInAggregationMultiFunctionHandler |
validateGetHandler(PlugInAggregationMultiFunctionValidationContext validationContext)
Called for each instance of use of any of the aggregation functions at validation time
after all declared aggregation have been added.
|
void addAggregationFunction(PlugInAggregationMultiFunctionDeclarationContext declarationContext)
declarationContext - contextPlugInAggregationMultiFunctionHandler validateGetHandler(PlugInAggregationMultiFunctionValidationContext validationContext)
validationContext - validationContext