org.apache.cassandra.cql3.selection

Class Selector

java.lang.Object

org.apache.cassandra.cql3.selection.Selector

All Implemented Interfaces:

AssignmentTestable

Direct Known Subclasses:

SimpleSelector

public abstract class Selector
extends java.lang.Object
implements AssignmentTestable

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.

Nested classes/interfaces inherited from interface org.apache.cassandra.cql3.AssignmentTestable

AssignmentTestable.TestResult

Constructor Summary

Constructors

Constructor and Description
Selector()

Method Summary

Modifier and Type	Method and Description
abstract void	addInput(int protocolVersion, Selection.ResultSetBuilder rs) Add the current value from the specified ResultSetBuilder.
abstract java.nio.ByteBuffer	getOutput(int protocolVersion) Returns the selector output.
abstract AbstractType<?>	getType() Returns the Selector output type.
boolean	isAggregate() Checks if this Selector is creating aggregates.
abstract void	reset() Reset the internal state of this Selector.
AssignmentTestable.TestResult	testAssignment(java.lang.String keyspace, ColumnSpecification receiver)

Methods inherited from class java.lang.Object

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

Constructor Detail

Selector

public Selector()

Method Detail

addInput

public abstract void addInput(int protocolVersion,
                              Selection.ResultSetBuilder rs)
                       throws InvalidRequestException

Add the current value from the specified ResultSetBuilder.

Parameters:

protocolVersion - protocol version used for serialization

rs - the ResultSetBuilder

Throws:

InvalidRequestException - if a problem occurs while add the input value

getOutput

public abstract java.nio.ByteBuffer getOutput(int 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.

isAggregate

public boolean isAggregate()

Checks if this Selector is creating aggregates.

Returns:

true if this Selector is creating aggregates false otherwise.

reset

public abstract void reset()

Reset the internal state of this Selector.

testAssignment

public final AssignmentTestable.TestResult testAssignment(java.lang.String keyspace,
                                                          ColumnSpecification receiver)

Specified by:

testAssignment in interface AssignmentTestable

Returns:

whether this object can be assigned to the provided receiver. We distinguish between 3 values: - EXACT_MATCH if this object is exactly of the type expected by the receiver - WEAKLY_ASSIGNABLE if this object is not exactly the expected type but is assignable nonetheless - NOT_ASSIGNABLE if it's not assignable Most caller should just call the isAssignable() method on the result, though functions have a use for testing "strong" equality to decide the most precise overload to pick when multiple could match.