saffron.rel
Class ExtenderAggregation

java.lang.Object
  |
  +--saffron.rel.ExtenderAggregation

All Implemented Interfaces:

Aggregation

public class ExtenderAggregation

extends Object

implements Aggregation

ExtenderAggregation is an aggregation which works by instantiating a user-defined aggregation (AggregationExtender), as opposed to generating custom code.

Two bugs with the current implementation of implementStart(saffron.opt.Implementor, saffron.rel.Rel, int[]) etc. First, the aggregation expression should be evaluated only once -- when the query starts -- and stored in a variable. I guess it should be added to the environment holding the query.

Second, we pass real expressions as the values of the dummy arguments to implementStart(saffron.opt.Implementor, saffron.rel.Rel, int[]) and implementResult(openjava.ptree.Expression). This is inefficient, but moreover, it is conceivable that the expressions will not be valid in the scope where start and result are executed.

Since:

3 February, 2002

Version:

$Id: //open/saffron/src/main/saffron/rel/ExtenderAggregation.java#2 $

Author:

jhyde

Field Summary

(package private) OJClass	aggClazz
(package private) Expression	aggExp
(package private) OJMethod	aggregateMethod
(package private) OJClass[]	argTypes
(package private) OJMethod	mergeMethod
(package private) OJMethod	nextMethod
(package private) OJMethod	resultMethod
(package private) OJMethod	startMethod

Constructor Summary

(package private)

ExtenderAggregation(Expression aggExp, Environment env, OJClass[] argTypes)

Method Summary

boolean	canMerge() Whether this aggregation can merge together two accumulators.
private static OJMethod	findMethod(OJClass aggClazz, String name, OJClass[] argTypes, int extra, OJClass desiredType, boolean fail)
OJClass[]	getParameterTypes()
OJClass	getReturnType()
void	implementMerge(Implementor implementor, Rel rel, Expression accumulator, Expression otherAccumulator) Generates (into the current statement list, gleaned by calling implementor's Implementor.getStatementList() method) code to merge two accumulators.
void	implementNext(Implementor implementor, Rel rel, Expression accumulator, int[] args) Generates (into the current statement list, gleaned by calling implementor's Implementor.getStatementList() method) the piece of code which gets called each time an extra row is seen.
Expression	implementResult(Expression accumulator) Generates the expression which gets called when a total is complete.
Expression	implementStart(Implementor implementor, Rel rel, int[] args) Generates the expression which gets called when a new total is created.
Expression	implementStartAndNext(Implementor implementor, Rel rel, int[] args) Generates code to create a new total and to add the first value.
static boolean	matches(OJClass aggClazz, OJClass[] argTypes) Returns whether this aggregation has an overloading which matches the given name and argument types.

Methods inherited from class java.lang.Object

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

Field Detail

aggExp

Expression aggExp

aggClazz

OJClass aggClazz

argTypes

OJClass[] argTypes

aggregateMethod

OJMethod aggregateMethod

startMethod

OJMethod startMethod

nextMethod

OJMethod nextMethod

mergeMethod

OJMethod mergeMethod

resultMethod

OJMethod resultMethod

Constructor Detail

ExtenderAggregation

ExtenderAggregation(Expression aggExp,
                    Environment env,
                    OJClass[] argTypes)

Method Detail

matches

public static boolean matches(OJClass aggClazz,
                              OJClass[] argTypes)

Returns whether this aggregation has an overloading which matches the given name and argument types.

findMethod

private static OJMethod findMethod(OJClass aggClazz,
                                   String name,
                                   OJClass[] argTypes,
                                   int extra,
                                   OJClass desiredType,
                                   boolean fail)

getReturnType

public OJClass getReturnType()

Specified by:

getReturnType in interface Aggregation

getParameterTypes

public OJClass[] getParameterTypes()

Specified by:

getParameterTypes in interface Aggregation

canMerge

public boolean canMerge()

Description copied from interface: Aggregation

Whether this aggregation can merge together two accumulators. count can (you just add the accumulators); avg and Nth cannot.

Specified by:

canMerge in interface Aggregation

implementStart

public Expression implementStart(Implementor implementor,
                                 Rel rel,
                                 int[] args)

Description copied from interface: Aggregation

Generates the expression which gets called when a new total is created. For sum(x), this looks like new saffron.runtime.Holder.int_Holder(0).

Specified by:

implementStart in interface Aggregation

implementStartAndNext

public Expression implementStartAndNext(Implementor implementor,
                                        Rel rel,
                                        int[] args)

Description copied from interface: Aggregation

Generates code to create a new total and to add the first value. For sum(x), this looks like new saffron.runtime.Holder.int_Holder(x).

Specified by:

implementStartAndNext in interface Aggregation

implementNext

public void implementNext(Implementor implementor,
                          Rel rel,
                          Expression accumulator,
                          int[] args)

Description copied from interface: Aggregation

Generates (into the current statement list, gleaned by calling implementor's Implementor.getStatementList() method) the piece of code which gets called each time an extra row is seen. For sum(x), this looks like ((saffron.runtime.Holder.int_Holder) accumulator).value += x.

Specified by:

implementNext in interface Aggregation

Parameters:

implementor - a callback object which knows how to generate things

rel - the relational expression which is generating this code

accumulator - the expression which holds the total

args - the ordinals of the fields of the child row which are arguments to this aggregation

implementMerge

public void implementMerge(Implementor implementor,
                           Rel rel,
                           Expression accumulator,
                           Expression otherAccumulator)

Description copied from interface: Aggregation

Generates (into the current statement list, gleaned by calling implementor's Implementor.getStatementList() method) code to merge two accumulators. For sum(x), this looks like ((saffron.runtime.Holder.int_Holder) accumulator).value += ((saffron.runtime.Holder.int_Holder) other).value.

The method is only called if Aggregation.canMerge() returns true.

Specified by:

implementMerge in interface Aggregation

Parameters:

implementor - a callback object which knows how to generate things

rel - the relational expression which is generating this code

accumulator - the expression which holds the total

otherAccumulator - accumulator to merge in

implementResult

public Expression implementResult(Expression accumulator)

Description copied from interface: Aggregation

Generates the expression which gets called when a total is complete. For sum(x), this looks like ((saffron.runtime.Holder.int_Holder) accumulator).value.

Specified by:

implementResult in interface Aggregation