T- the type of the table aggregation result
ACC- the type of the table aggregation accumulator. The accumulator is used to keep the aggregated values which are needed to compute an aggregation result. TableAggregateFunction represents its state using accumulator, thereby the state of the TableAggregateFunction must be put into the accumulator.
@PublicEvolving public abstract class TableAggregateFunction<T,ACC> extends UserDefinedAggregateFunction<T,ACC>
There is another method that can be optional to have:
All these methods must be declared publicly, not static, and named exactly as the names
mentioned above. The method
UserDefinedAggregateFunction.createAccumulator() is defined in
UserDefinedAggregateFunction functions, while other methods are explained below.
Processes the input values and update the provided accumulator instance. The method accumulate can be overloaded with different custom types and arguments. A TableAggregateFunction requires at least one accumulate() method. param: accumulator the accumulator which contains the current aggregated results param: [user defined inputs] the input value (usually obtained from a new arrived data). public void accumulate(ACC accumulator, [user defined inputs])
Retracts the input values from the accumulator instance. The current design assumes the inputs are the values that have been previously accumulated. The method retract can be overloaded with different custom types and arguments. param: accumulator the accumulator which contains the current aggregated results param: [user defined inputs] the input value (usually obtained from a new arrived data). public void retract(ACC accumulator, [user defined inputs])
Called every time when an aggregation result should be materialized. The returned value could be either an early and incomplete result (periodically emitted as data arrive) or the final result of the aggregation. param: accumulator the accumulator which contains the current aggregated results param: out the collector used to output data. public void emitValue(ACC accumulator, Collector<T> out)
Called every time when an aggregation result should be materialized. The returned value could be either an early and incomplete result (periodically emitted as data arrive) or the final result of the aggregation. Different from emitValue, emitUpdateWithRetract is used to emit values that have been updated. This method outputs data incrementally in retract mode, i.e., once there is an update, we have to retract old records before sending new updated ones. The emitUpdateWithRetract method will be used in preference to the emitValue method if both methods are defined in the table aggregate function, because the method is treated to be more efficient than emitValue as it can output values incrementally. param: accumulator the accumulator which contains the current aggregated results param: out the retractable collector used to output data. Use collect method to output(add) records and use retract method to retract(delete) records. public void emitUpdateWithRetract(ACC accumulator, RetractableCollector<T> out)
|Modifier and Type||Class and Description|
Collects a record and forwards it.
|Constructor and Description|
|Modifier and Type||Method and Description|
Returns the kind of function this definition describes.
Returns the logic for performing type inference of a call to this function definition.
createAccumulator, getAccumulatorType, getResultType
close, functionIdentifier, open, toString
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
public final FunctionKind getKind()
public TypeInference getTypeInference(DataTypeFactory typeFactory)
The type inference process is responsible for inferring unknown types of input arguments, validating input arguments, and producing result types. The type inference process happens independent of a function body. The output of the type inference is used to search for a corresponding runtime implementation.
Instances of type inference can be created by using
BuiltInFunctionDefinitions for concrete usage examples.
The type inference for user-defined functions is automatically extracted using reflection. It
does this by analyzing implementation methods such as
eval() or accumulate() and the generic
parameters of a function class if present. If the reflective information is not sufficient, it can
be supported and enriched with
Note: Overriding this method is only recommended for advanced users. If a custom type inference is specified, it is the responsibility of the implementer to make sure that the output of the type inference process matches with the implementation method:
The implementation method must comply with each
by the type inference. For example, if
is an expected argument type, the method must accept a call
Regular Java calling semantics (including type widening and autoboxing) are applied when calling
an implementation method which means that the signature can be
The runtime will take care of converting the data to the data format specified by the
DataType.getConversionClass() coming from the type inference logic.
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