com.apple.foundationdb.record.metadata.expressions

Class ListKeyExpression

java.lang.Object

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

com.apple.foundationdb.record.metadata.expressions.ListKeyExpression

All Implemented Interfaces:

KeyExpression, KeyExpressionWithChildren, PlanHashable

@API(value=MAINTAINED)
public class ListKeyExpression
extends BaseKeyExpression
implements KeyExpressionWithChildren

Combine keys from zero or more child keys.

Form a cross-product similar to ThenKeyExpression, but producing lists containing each child's evaluation result rather than concatenating. When converted to a Tuple, the nth child corresponds to tuple.getNestedTuple(n), which is less compact on disk but easier to find the child boundaries in.

Consider the expressions concat(field("child_1").nest(field("field_1")), field("child_2").nest(concat(field("field_1"), field("field_2"))) and concat(field("child_1").nest(concat(field("field_1"), field("field_2"))), field("child_2").nest(field("field_1"))). These might produce values like [[1.1, 2.1, 2.2]] and [[1.1, 1.2, 2.1]], respectively. Recovering the first child's contribution means remembering it or at least its KeyExpression.getColumnSize(), to know where the boundary is.

Contrast list(field("child_1").nest(field("field_1")), field("child_2").nest(concat(field("field_1"), field("field_2"))) and list(field("child_1").nest(concat(field("field_1"), field("field_2"))), field("child_2").nest(field("field_1"))). These would produce [[[1.1], [2.1, 2.2]]] and [[[1.1, 1.2], [2.1]]], respectively.

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

Constructor Summary

Constructors

Constructor and Description
ListKeyExpression(List<KeyExpression> exprs)
ListKeyExpression(RecordMetaDataProto.List list)

Method Summary

Modifier and Type	Method and 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.
List<KeyExpression>	getChildren()
int	getColumnSize() Returns the number of items in each KeyValue that will be returned.
KeyExpression	getSubKeyImpl(int start, int end)
int	hashCode()
boolean	hasRecordTypeKey() Check whether a key expression uses record type key in some way.
List<KeyExpression>	normalizeKeyForPositions() Get key in normalized form for comparing field-by-field.
int	planHash() Return a hash similar to hashCode, but with the additional guarantee that is is stable across JVMs.
RecordMetaDataProto.KeyExpression	toKeyExpression()
RecordMetaDataProto.List	toProto()
String	toString()
List<Descriptors.FieldDescriptor>	validate(Descriptors.Descriptor descriptor) Validate this expression against a given record type descriptor.
int	versionColumns() Returns the number of version columns produced by this key expression.

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

getSubKey, 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, fromProto, getSubKey, hasProperInterfaces, isPrefixKey

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

combineHashes, iterablePlanHash, objectPlanHash, objectsPlanHash, planHash, planHash, planHashUnordered, stringHashUnordered

Constructor Detail

ListKeyExpression

public ListKeyExpression(@Nonnull
                         List<KeyExpression> exprs)

ListKeyExpression

public ListKeyExpression(@Nonnull
                         RecordMetaDataProto.List list)
                  throws KeyExpression.DeserializationException

Throws:

KeyExpression.DeserializationException

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()

Returns the number of items in each KeyValue that will be returned. Note that this is exactly the number of child expressions, rather than the sum of their sizes, because each one becomes a separate nested tuple.

Specified by:

getColumnSize in interface KeyExpression

Returns:

the number of elements that will be produced for every key

toProto

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

Specified by:

toProto in interface KeyExpression

Throws:

KeyExpression.SerializationException

toKeyExpression

@Nonnull
public RecordMetaDataProto.KeyExpression toKeyExpression()

Specified by:

toKeyExpression in interface KeyExpression

normalizeKeyForPositions

@Nonnull
public List<KeyExpression> normalizeKeyForPositions()

Description copied from interface: KeyExpression

Get key in normalized form for comparing field-by-field. Does not take account of fan-type, so only valid when this has already been taken care of, such as individual index entries.

Specified by:

normalizeKeyForPositions in interface KeyExpression

Returns:

a list of key expressions in order

versionColumns

public int versionColumns()

Description copied from interface: KeyExpression

Returns the number of version columns produced by this key expression.

Specified by:

versionColumns in interface KeyExpression

Returns:

the number of version columns

hasRecordTypeKey

public boolean hasRecordTypeKey()

Description copied from interface: KeyExpression

Check whether a key expression uses record type key in some way.

Specified by:

hasRecordTypeKey in interface KeyExpression

Returns:

true if record type key is used

getSubKeyImpl

public KeyExpression getSubKeyImpl(int start,
                                   int end)

Overrides:

getSubKeyImpl in class BaseKeyExpression

getChildren

@Nonnull
public List<KeyExpression> getChildren()

Specified by:

getChildren in interface KeyExpressionWithChildren

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()

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

Returns:

a stable hash code