Package org.hibernate.search.engine.search.projection.spi

Interface ProjectionAccumulator<E,V,A,R>

Type Parameters:

E - The type of extracted values to accumulate before being transformed.

V - The type of values to accumulate obtained by transforming extracted values (E).

A - The type of the temporary storage for accumulated values, before and after being transformed.

R - The type of the final result containing values of type V.

public interface ProjectionAccumulator<E,V,A,R>

A variation on Collector suitable for projections on field values.

Compared to Collector:

• There is no concept of parallel execution.
• All operations are expected to be non-blocking, except for transformAll(Object, ProjectionConverter, FromDocumentValueConvertContext) and finish(Object).
• Values to accumulate are expected to be transformed exactly once after accumulation, changing their type from ProjectionAccumulator to ProjectionAccumulator. Clients are responsible for ensuring values to accumulate have been transformed upon calling finish(Object).

Nested Class Summary

Nested Classes

Modifier and Type	Interface	Description
static interface	ProjectionAccumulator.Provider<U,R>	Provides an accumulator for a given type of values to accumulate (T).

Method Summary

Modifier and Type	Method	Description
A	accumulate(A accumulated, E value)	Folds a new value in the given accumulated container.
default A	accumulateAll(A accumulated, Collection<E> values)	Folds a collection of new values in the given accumulated container.
A	createInitial()	Creates the initial accumulated container.
R	finish(A accumulated)	Finishes the accumulation, converting the accumulated container into the final result.
E	get(A accumulated, int index)	Retrieves the value at the given index.
static <V> ProjectionAccumulator.Provider<V,List<V>>	list()
static <V> ProjectionAccumulator.Provider<V,V>	single()
int	size(A accumulated)
A	transform(A accumulated, int index, V transformed)	Transforms the value at the given index, replacing it with the given transformed value.
default A	transformAll(A accumulated, ProjectionConverter<? super E,? extends V> converter, FromDocumentValueConvertContext context)	Transforms all values with the given converter and the given context.

Method Detail

single

static <V> ProjectionAccumulator.Provider<V,V> single()

list

static <V> ProjectionAccumulator.Provider<V,List<V>> list()

createInitial

A createInitial()

Creates the initial accumulated container.

This operation should be non-blocking.

Returns:

The initial accumulated container, to pass to the first call to accumulate(Object, Object).

accumulate

A accumulate(A accumulated,
             E value)

Folds a new value in the given accumulated container.

This operation should be non-blocking.

Parameters:

accumulated - The accumulated value so far. For the first call, this is a value returned by createInitial(). For the next calls, this is the value returned by the previous call to accumulate(Object, Object).

value - The value to accumulate.

Returns:

The new accumulated value.

accumulateAll

default A accumulateAll(A accumulated,
                        Collection<E> values)

Folds a collection of new values in the given accumulated container.

This operation should be non-blocking.

Parameters:

accumulated - The accumulated value so far. For the first call, this is a value returned by createInitial(). For the next calls, this is the value returned by the previous call to accumulate(Object, Object).

values - The values to accumulate.

Returns:

The new accumulated value.

size

int size(A accumulated)

Parameters:

accumulated - The accumulated value so far, returned by the last call to accumulate(Object, Object).

Returns:

The number of elements in the accumulated value.

get

E get(A accumulated,
      int index)

Retrieves the value at the given index.

This operation should be non-blocking.

Parameters:

accumulated - The accumulated value so far, returned by the last call to accumulate(Object, Object).

index - The index of the value to retrieve.

Returns:

The value at the given index.

transform

A transform(A accumulated,
            int index,
            V transformed)

Transforms the value at the given index, replacing it with the given transformed value.

This operation should be non-blocking.

Parameters:

accumulated - The accumulated value so far, returned by the last call to accumulate(Object, Object).

index - The index of the value being transformed.

transformed - The transformed value.

Returns:

The new accumulated value.

transformAll

default A transformAll(A accumulated,
                       ProjectionConverter<? super E,? extends V> converter,
                       FromDocumentValueConvertContext context)

Transforms all values with the given converter and the given context.

This operation may be blocking.

Parameters:

accumulated - The accumulated value so far, returned by the last call to accumulate(Object, Object).

converter - The projection converter (from F to V).

context - The context to be passed to the projection converter.

Returns:

The new accumulated value.

finish

R finish(A accumulated)

Finishes the accumulation, converting the accumulated container into the final result.

This operation may be blocking.

Parameters:

accumulated - The temporary storage created by createInitial(), then populated by successive calls to accumulate(Object, Object), then transformed by a single call to transformAll(Object, ProjectionConverter, FromDocumentValueConvertContext) or by successive calls to transform(Object, int, Object).

Returns:

The final result of the accumulation.