Package com.apple.foundationdb.record.metadata.expressions

Class EmptyKeyExpression

java.lang.Object

com.apple.foundationdb.record.metadata.expressions.BaseKeyExpression

com.apple.foundationdb.record.metadata.expressions.EmptyKeyExpression

All Implemented Interfaces:

KeyExpression, KeyExpressionWithoutChildren, PlanHashable, QueryHashable

@API(MAINTAINED)
public class EmptyKeyExpression
extends BaseKeyExpression
implements KeyExpression, KeyExpressionWithoutChildren

A single empty key.

Nested Class Summary

Nested classes/interfaces inherited from class com.apple.foundationdb.record.metadata.expressions.BaseKeyExpression

BaseKeyExpression.IllegalSubKeyException, BaseKeyExpression.UnsplittableKeyExpressionException

Nested classes/interfaces inherited from interface com.apple.foundationdb.record.metadata.expressions.KeyExpression

KeyExpression.DeserializationException, KeyExpression.FanType, KeyExpression.InvalidExpressionException, KeyExpression.InvalidResultException, KeyExpression.NoSuchArgumentException, KeyExpression.SerializationException

Nested classes/interfaces inherited from interface com.apple.foundationdb.record.PlanHashable

PlanHashable.PlanHashKind

Nested classes/interfaces inherited from interface com.apple.foundationdb.record.QueryHashable

QueryHashable.QueryHashKind

Field Summary

Fields

Modifier and Type	Field	Description
static EmptyKeyExpression	EMPTY
static RecordMetaDataProto.KeyExpression	EMPTY_PROTO

Method Summary

Modifier and Type	Method	Description
boolean	createsDuplicates()	This states whether the given expression type is capable of evaluating more to more than one value when applied to a single record.
boolean	equals(Object o)
<M extends Message> List<Key.Evaluated>	evaluateMessage(FDBRecord<M> record, Message message)	Evaluate this expression against a record or a Protobuf message.
<S extends KeyExpressionVisitor.State> GraphExpansion	expand(ExpansionVisitor<S> visitor)	Expand this key expression into a data flow graph.
int	getColumnSize()	Returns the number of items in each KeyValue that will be returned.
GroupingKeyExpression	groupBy(KeyExpression groupByFirst, KeyExpression... groupByRest)
int	hashCode()
int	planHash(PlanHashable.PlanHashKind hashKind)	Return a hash similar to hashCode, but with the additional guarantee that is is stable across JVMs.
int	queryHash(QueryHashable.QueryHashKind hashKind)	Return a hash similar to hashCode, but with the additional guarantee that is is stable across JVMs.
RecordMetaDataProto.KeyExpression	toKeyExpression()
RecordMetaDataProto.Empty	toProto()
String	toString()
List<Descriptors.FieldDescriptor>	validate(Descriptors.Descriptor descriptor)	Validate this expression against a given record type descriptor.

Methods inherited from class com.apple.foundationdb.record.metadata.expressions.BaseKeyExpression

getSubKey, getSubKeyImpl, isPrefixKey

Methods inherited from class java.lang.Object

clone, finalize, getClass, notify, notifyAll, wait, wait, wait

Methods inherited from interface com.apple.foundationdb.record.metadata.expressions.KeyExpression

evaluate, evaluateSingleton, getSubKey, hasLosslessNormalization, hasProperInterfaces, hasRecordTypeKey, isPrefixKey, normalizeKeyForPositions, versionColumns

Methods inherited from interface com.apple.foundationdb.record.PlanHashable

planHash

Field Detail

EMPTY

public static final EmptyKeyExpression EMPTY

EMPTY_PROTO

public static final RecordMetaDataProto.KeyExpression EMPTY_PROTO

Method Detail

evaluateMessage

@Nonnull
public <M extends Message> List<Key.Evaluated> evaluateMessage(@Nullable
                                                               FDBRecord<M> record,
                                                               @Nullable
                                                               Message message)

Description copied from interface: KeyExpression

Evaluate this expression against a record or a Protobuf message. The message might be the Protobuf form of a record or a piece of that record. If the key expression is meaningful against a subrecord, it should evaluate against the message. Otherwise, it should evaluate against the record and ignore what part of that record is being considered. There should not be any reason to call this method outside of the implementation of another evaluateMessage. Under ordinary circumstances, if record is null, then message will be null. Otherwise, message will be record.getRecord() or some submessage of that, possibly null if the corresponding field is missing.

Specified by:

evaluateMessage in interface KeyExpression

Type Parameters:

M - the type of record

Parameters:

record - the record

message - the Protobuf message to evaluate against

Returns:

the evaluated keys for the given record

See Also:

KeyExpression.evaluate(com.apple.foundationdb.record.provider.foundationdb.FDBRecord<M>)

createsDuplicates

public boolean createsDuplicates()

Description copied from interface: KeyExpression

This states whether the given expression type is capable of evaluating more to more than one value when applied to a single record. In practice, this can happen if this expression is evaluated on a repeated field with FanType.FanOut set (either directly or indirectly).

Specified by:

createsDuplicates in interface KeyExpression

Returns:

true if this expression can evaluate to multiple values and false otherwise

validate

public List<Descriptors.FieldDescriptor> validate(@Nonnull
                                                  Descriptors.Descriptor descriptor)

Description copied from interface: KeyExpression

Validate this expression against a given record type descriptor.

Specified by:

validate in interface KeyExpression

Parameters:

descriptor - the descriptor for the record type or submessage

Returns:

a list of fields that this key applies to

getColumnSize

public int getColumnSize()

Description copied from interface: KeyExpression

Returns the number of items in each KeyValue that will be returned. For key expressions that support KeyExpression.FanType.Concatenate, this will the count of non-nested lists, i.e. this will be value of evaluate(r).get(i).toList().size() for any i or r.

Specified by:

getColumnSize in interface KeyExpression

Returns:

the number of elements that will be produced for every key

toProto

@Nonnull
public RecordMetaDataProto.Empty toProto()
                                  throws KeyExpression.SerializationException

Specified by:

toProto in interface KeyExpression

Throws:

KeyExpression.SerializationException

expand

@Nonnull
public <S extends KeyExpressionVisitor.State> GraphExpansion expand(@Nonnull
                                                                    ExpansionVisitor<S> visitor)

Description copied from interface: KeyExpression

Expand this key expression into a data flow graph. The returned graph represents an adequate representation of the key expression as composition of relational expressions and operators (RelationalExpressions). Note that implementors should defer to the visitation methods in the supplied visitor rather than encoding actual logic in an overriding method.

Specified by:

expand in interface KeyExpression

Type Parameters:

S - a type that reflects the state that visitor uses

Parameters:

visitor - a ExpansionVisitor that is created by the caller from a data structure that reflects the specific semantics of the key expression. Normally this visitor is directly created based on an index.

Returns:

a new GraphExpansion representing the query graph equivalent of this key expression using the supplied visitor

See Also:

QueryComponent.expand(com.apple.foundationdb.record.query.plan.temp.CorrelationIdentifier)

toKeyExpression

@Nonnull
public RecordMetaDataProto.KeyExpression toKeyExpression()

Specified by:

toKeyExpression in interface KeyExpression

groupBy

@Nonnull
public GroupingKeyExpression groupBy(@Nonnull
                                     KeyExpression groupByFirst,
                                     @Nonnull
                                     KeyExpression... groupByRest)

toString

public String toString()

Overrides:

toString in class Object

equals

public boolean equals(Object o)

Overrides:

equals in class Object

hashCode

public int hashCode()

Overrides:

hashCode in class Object

planHash

public int planHash(@Nonnull
                    PlanHashable.PlanHashKind hashKind)

Description copied from interface: PlanHashable

Return a hash similar to hashCode, but with the additional guarantee that is is stable across JVMs.

Specified by:

planHash in interface PlanHashable

Parameters:

hashKind - the "kind" of hash to calculate. Each kind of hash has a particular logic with regards to included and excluded items.

Returns:

a stable hash code

queryHash

public int queryHash(@Nonnull
                     QueryHashable.QueryHashKind hashKind)

Description copied from interface: QueryHashable

Return a hash similar to hashCode, but with the additional guarantee that is is stable across JVMs.

Specified by:

queryHash in interface QueryHashable

Parameters:

hashKind - the "kind" of hash to calculate. Each kind of hash has a particular logic with regards to included and excluded items.

Returns:

a stable hash code