org.apache.cassandra.cql3.selection

Class Selector

java.lang.Object

org.apache.cassandra.cql3.selection.Selector

Direct Known Subclasses:

SimpleSelector, TermSelector

public abstract class Selector
extends java.lang.Object

A Selector is used to convert the data returned by the storage engine into the data requested by the user. They correspond to the <selector> elements from the select clause.

Since the introduction of aggregation, Selectors cannot be called anymore by multiple threads as they have an internal state.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
static class	Selector.Factory A factory for Selector instances.
static class	Selector.InputRow A row of data that need to be processed by a Selector
static class	Selector.Kind The Selector kinds.
protected static class	Selector.SelectorDeserializer
static class	Selector.Serializer

Field Summary

Fields

Modifier and Type	Field and Description
static Selector.Serializer	serializer The Selector serializer.

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	Selector(Selector.Kind kind)

Method Summary

Modifier and Type	Method and Description
abstract void	addFetchedColumns(ColumnFilter.Builder builder) Add to the provided builder the column (and potential subselections) to fetch for this selection.
abstract void	addInput(ProtocolVersion protocolVersion, Selector.InputRow input) Add the current value from the specified ResultSetBuilder.
abstract java.nio.ByteBuffer	getOutput(ProtocolVersion protocolVersion) Returns the selector output.
abstract AbstractType<?>	getType() Returns the Selector output type.
boolean	isTerminal() A selector is terminal if it doesn't require any input for it's output to be computed, i.e.
Selector.Kind	kind() Returns the Selector kind.
abstract void	reset() Reset the internal state of this Selector.
protected abstract void	serialize(DataOutputPlus out, int version)
protected abstract int	serializedSize(int version)
protected static int	sizeOf(AbstractType<?> type)
void	validateForGroupBy() Checks that this selector is valid for GROUP BY clause.
protected static void	writeType(DataOutputPlus out, AbstractType<?> type)

Methods inherited from class java.lang.Object

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

Field Detail

serializer

public static final Selector.Serializer serializer

The Selector serializer.

Constructor Detail

Selector

protected Selector(Selector.Kind kind)

Method Detail

kind

public final Selector.Kind kind()

Returns the Selector kind.

Returns:

the Selector kind

addFetchedColumns

public abstract void addFetchedColumns(ColumnFilter.Builder builder)

Add to the provided builder the column (and potential subselections) to fetch for this selection.

Parameters:

builder - the builder to add columns and subselections to.

addInput

public abstract void addInput(ProtocolVersion protocolVersion,
                              Selector.InputRow input)

Add the current value from the specified ResultSetBuilder.

Parameters:

protocolVersion - protocol version used for serialization

input - the input row

Throws:

InvalidRequestException - if a problem occurs while adding the input row

getOutput

public abstract java.nio.ByteBuffer getOutput(ProtocolVersion protocolVersion)
                                       throws InvalidRequestException

Returns the selector output.

Parameters:

protocolVersion - protocol version used for serialization

Returns:

the selector output

Throws:

InvalidRequestException - if a problem occurs while computing the output value

getType

public abstract AbstractType<?> getType()

Returns the Selector output type.

Returns:

the Selector output type.

reset

public abstract void reset()

Reset the internal state of this Selector.

isTerminal

public boolean isTerminal()

A selector is terminal if it doesn't require any input for it's output to be computed, i.e. if getOutput(org.apache.cassandra.transport.ProtocolVersion) result doesn't depend of addInput(org.apache.cassandra.transport.ProtocolVersion, org.apache.cassandra.cql3.selection.Selector.InputRow). This is typically the case of a constant value or functions on constant values.

validateForGroupBy

public void validateForGroupBy()

Checks that this selector is valid for GROUP BY clause.

serializedSize

protected abstract int serializedSize(int version)

serialize

protected abstract void serialize(DataOutputPlus out,
                                  int version)
                           throws java.io.IOException

Throws:

java.io.IOException

writeType

protected static void writeType(DataOutputPlus out,
                                AbstractType<?> type)
                         throws java.io.IOException

Throws:

java.io.IOException

sizeOf

protected static int sizeOf(AbstractType<?> type)