Class IntersectionCursor<T>
- java.lang.Object
-
- com.apple.foundationdb.record.provider.foundationdb.cursors.MergeCursor<T,U,com.apple.foundationdb.record.provider.foundationdb.cursors.KeyedMergeCursorState<T>>
-
- com.apple.foundationdb.record.provider.foundationdb.cursors.IntersectionCursor<T>
-
- Type Parameters:
T
- the type of elements returned by the cursor
- All Implemented Interfaces:
RecordCursor<T>
,AutoCloseable
,Iterator<T>
@API(MAINTAINED) public class IntersectionCursor<T> extends MergeCursor<T,U,com.apple.foundationdb.record.provider.foundationdb.cursors.KeyedMergeCursorState<T>>
A cursor that implements an intersection of matching elements from a set of cursors all of whom are ordered compatibly. For every matching set, this will return the element from the first child cursor. If each cursor returns something slightly different and the use case requires accessing the different results from each child, then one should use theIntersectionMultiCursor
which returns a list of the child cursor values rather than just the first one.- See Also:
IntersectionMultiCursor
-
-
Nested Class Summary
-
Nested classes/interfaces inherited from interface com.apple.foundationdb.record.RecordCursor
RecordCursor.NoNextReason
-
-
Method Summary
All Methods Static Methods Instance Methods Concrete Methods Modifier and Type Method Description protected CompletableFuture<List<com.apple.foundationdb.record.provider.foundationdb.cursors.KeyedMergeCursorState<T>>>
computeNextResultStates()
Compute the next result states for the cursor based on the status of the existing states.static <M extends Message,S extends FDBRecord<M>>
IntersectionCursor<S>create(FDBRecordStoreBase<M> store, KeyExpression comparisonKey, boolean reverse, Function<byte[],RecordCursor<S>> left, Function<byte[],RecordCursor<S>> right, byte[] continuation)
Create an intersection cursor from two compatibly-ordered cursors.static <M extends Message,S extends FDBRecord<M>>
IntersectionCursor<S>create(FDBRecordStoreBase<M> store, KeyExpression comparisonKey, boolean reverse, List<Function<byte[],RecordCursor<S>>> cursorFunctions, byte[] continuation)
Create an intersection cursor from two or more compatibly-ordered cursors.static <T> IntersectionCursor<T>
create(Function<? super T,? extends List<Object>> comparisonKeyFunction, boolean reverse, Function<byte[],RecordCursor<T>> left, Function<byte[],RecordCursor<T>> right, byte[] continuation, FDBStoreTimer timer)
Create an intersection cursor from two compatibly-ordered cursors.static <T> IntersectionCursor<T>
create(Function<? super T,? extends List<Object>> comparisonKeyFunction, boolean reverse, List<Function<byte[],RecordCursor<T>>> cursorFunctions, byte[] continuation, FDBStoreTimer timer)
Create an intersection cursor from two or more compatibly-ordered cursors.protected static <T> List<com.apple.foundationdb.record.provider.foundationdb.cursors.KeyedMergeCursorState<T>>
createCursorStates(Function<byte[],RecordCursor<T>> left, Function<byte[],RecordCursor<T>> right, byte[] byteContinuation, Function<? super T,? extends List<Object>> comparisonKeyFunction)
protected static <T> List<com.apple.foundationdb.record.provider.foundationdb.cursors.KeyedMergeCursorState<T>>
createCursorStates(List<Function<byte[],RecordCursor<T>>> cursorFunctions, byte[] byteContinuation, Function<? super T,? extends List<Object>> comparisonKeyFunction)
protected Function<? super T,? extends List<Object>>
getComparisonKeyFunction()
com.apple.foundationdb.record.provider.foundationdb.cursors.IntersectionCursorContinuation
getContinuationObject()
Produce aRecordCursorContinuation
for this cursor.protected T
getNextResult(List<com.apple.foundationdb.record.provider.foundationdb.cursors.KeyedMergeCursorState<T>> cursorStates)
Determine the next result to return based on the results of the child cursors.protected RecordCursor.NoNextReason
mergeNoNextReasons()
Merges all of the cursors and whether they have stopped and returns the "weakest" reason for the result to stop.-
Methods inherited from class com.apple.foundationdb.record.provider.foundationdb.cursors.MergeCursor
accept, checkNextStateTimeout, close, getChildContinuations, getContinuation, getCursorStates, getExecutor, getNoNextReason, getStrongestNoNextReason, getTimer, getWeakestNoNextReason, next, onHasNext, onNext, whenAll, whenAny
-
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait
-
Methods inherited from interface java.util.Iterator
forEachRemaining, remove
-
Methods inherited from interface com.apple.foundationdb.record.RecordCursor
asIterator, asList, filter, filterAsync, filterAsyncInstrumented, filterAsyncInstrumented, filterInstrumented, filterInstrumented, first, flatMapPipelined, forEach, forEachAsync, forEachResult, forEachResultAsync, getCount, getNext, hasNext, limitRowsTo, limitTo, map, mapEffect, mapEffect, mapPipelined, orElse, reduce, skip, skipThenLimit
-
-
-
-
Method Detail
-
getNextResult
protected T getNextResult(@Nonnull List<com.apple.foundationdb.record.provider.foundationdb.cursors.KeyedMergeCursorState<T>> cursorStates)
Description copied from class:MergeCursor
Determine the next result to return based on the results of the child cursors. This will be called with the return value ofMergeCursor.computeNextResultStates()
.- Specified by:
getNextResult
in classMergeCursor<T,T,com.apple.foundationdb.record.provider.foundationdb.cursors.KeyedMergeCursorState<T>>
- Parameters:
cursorStates
- the list of cursors to be included in the result- Returns:
- a result somehow combining the results of the input cursors
-
create
@Nonnull public static <M extends Message,S extends FDBRecord<M>> IntersectionCursor<S> create(@Nonnull FDBRecordStoreBase<M> store, @Nonnull KeyExpression comparisonKey, boolean reverse, @Nonnull Function<byte[],RecordCursor<S>> left, @Nonnull Function<byte[],RecordCursor<S>> right, @Nullable byte[] continuation)
Create an intersection cursor from two compatibly-ordered cursors. As its comparison key function, it will evaluate the provided comparison key on each record from each cursor. This otherwise behaves exactly the same way as the overload of this function that takes a function to extract a comparison key.- Type Parameters:
M
- the type of the Protobuf record elements of the cursorS
- the type of record wrapping a record of typeM
- Parameters:
store
- record store from which records will be fetchedcomparisonKey
- the key expression used to compare records from different cursorsreverse
- whether records are returned in descending or ascending order by the comparison keyleft
- a function to produce the firstRecordCursor
from a continuationright
- a function to produce the secondRecordCursor
from a continuationcontinuation
- any continuation from a previous scan- Returns:
- a cursor containing all records in both child cursors
- See Also:
create(Function, boolean, Function, Function, byte[], FDBStoreTimer)
-
create
@Nonnull public static <T> IntersectionCursor<T> create(@Nonnull Function<? super T,? extends List<Object>> comparisonKeyFunction, boolean reverse, @Nonnull Function<byte[],RecordCursor<T>> left, @Nonnull Function<byte[],RecordCursor<T>> right, @Nullable byte[] continuation, @Nullable FDBStoreTimer timer)
Create an intersection cursor from two compatibly-ordered cursors. This cursor is identical to the cursor that would be produced by calling the overload ofcreate()
that takes a list of cursors.- Type Parameters:
T
- the type of elements returned by the cursor- Parameters:
comparisonKeyFunction
- the function expression used to compare elements from different cursorsreverse
- whether records are returned in descending or ascending order by the comparison keyleft
- a function to produce the firstRecordCursor
from a continuationright
- a function to produce the secondRecordCursor
from a continuationcontinuation
- any continuation from a previous scantimer
- the timer used to instrument events- Returns:
- a cursor containing all elements in both child cursors
- See Also:
create(Function, boolean, List, byte[], FDBStoreTimer)
-
create
@Nonnull public static <M extends Message,S extends FDBRecord<M>> IntersectionCursor<S> create(@Nonnull FDBRecordStoreBase<M> store, @Nonnull KeyExpression comparisonKey, boolean reverse, @Nonnull List<Function<byte[],RecordCursor<S>>> cursorFunctions, @Nullable byte[] continuation)
Create an intersection cursor from two or more compatibly-ordered cursors. As its comparison key function, it will evaluate the provided comparison key on each record from each cursor. This otherwise behaves exactly the same way as the overload of this function that takes a function to extract a comparison key.- Type Parameters:
M
- the type of the Protobuf record elements of the cursorS
- the type of record wrapping a record of typeM
- Parameters:
store
- record store from which records will be fetchedcomparisonKey
- the key expression used to compare records from different cursorsreverse
- whether records are returned in descending or ascending order by the comparison keycursorFunctions
- a list of functions to produceRecordCursor
s from a continuationcontinuation
- any continuation from a previous scan- Returns:
- a cursor containing all records in all child cursors
- See Also:
create(Function, boolean, List, byte[], FDBStoreTimer)
-
create
@Nonnull public static <T> IntersectionCursor<T> create(@Nonnull Function<? super T,? extends List<Object>> comparisonKeyFunction, boolean reverse, @Nonnull List<Function<byte[],RecordCursor<T>>> cursorFunctions, @Nullable byte[] continuation, @Nullable FDBStoreTimer timer)
Create an intersection cursor from two or more compatibly-ordered cursors. Note that this will throw an error if the list of cursors does not have at least two elements. The returned cursor will return all elements that appear in all of the provided cursors, preserving order. All cursors must return elements in the same order, and that order should be determined by the comparison key function, i.e., ifreverse
isfalse
, then the elements should be returned in ascending order by that key, and ifreverse
istrue
, they should be returned in descending order. Additionally, if the comparison key function evaluates to the same value when applied to two elements (possibly from different cursors), then those two elements should be equal. In other words, the value of the comparison key should be the only necessary data that need to be extracted from each element returned by the child cursors to perform the intersection. Additionally, the provided comparison key function should not have any side-effects and should produce the same output every time it is applied to the same input.The cursors are provided as a list of functions rather than a list of
RecordCursor
s. These functions should create a newRecordCursor
instance with a given continuation appropriate for that cursor type. The value of that continuation will be determined by this function from thecontinuation
parameter for the intersection cursor as a whole.- Type Parameters:
T
- the type of elements returned by this cursor- Parameters:
comparisonKeyFunction
- the function evaluated to compare elements from different cursorsreverse
- whether records are returned in descending or ascending order by the comparison keycursorFunctions
- a list of functions to produceRecordCursor
s from a continuationcontinuation
- any continuation from a previous scantimer
- the timer used to instrument events- Returns:
- a cursor containing all records in all child cursors
-
computeNextResultStates
@Nonnull protected CompletableFuture<List<com.apple.foundationdb.record.provider.foundationdb.cursors.KeyedMergeCursorState<T>>> computeNextResultStates()
Compute the next result states for the cursor based on the status of the existing states. This should return a (not necessarily proper) sublist of this cursor's cursor states. By default, this assumes the cursors return results in a compatible order based on their comparison key and loops until they all have matching values. Extenders of this class may choose an alternative approach depending on the semantics of that cursor.To indicate that the intersection cursor should stop, this function should either return an empty list of states or a list containing at least one state that does not have a next item.
- Specified by:
computeNextResultStates
in classMergeCursor<T,U,com.apple.foundationdb.record.provider.foundationdb.cursors.KeyedMergeCursorState<T>>
- Returns:
- the list of states included in the next result
-
getComparisonKeyFunction
@Nonnull protected Function<? super T,? extends List<Object>> getComparisonKeyFunction()
-
mergeNoNextReasons
@Nonnull protected RecordCursor.NoNextReason mergeNoNextReasons()
Merges all of the cursors and whether they have stopped and returns the "weakest" reason for the result to stop. It will returnRecordCursor.NoNextReason.SOURCE_EXHAUSTED
if any of the cursors are exhausted. If any of the cursors have stopped due to an in-band limit, it will return an in-band limit as well. Finally, if all of the stopped cursors have done so due to hitting an out-of-band limit, it will return an out-of-band limit as well. Note that, in practice, because an intersection cursor will returnfalse
fromonHasNext
if any of its child cursors have stopped, it is likely that there are only a small number (maybe one or two) cursors that have actually stopped when this method is called (e.g., the first cursor to exhaust its source or the first cursor to hit a limit imposed by the element scan limiter).- Specified by:
mergeNoNextReasons
in classMergeCursor<T,U,com.apple.foundationdb.record.provider.foundationdb.cursors.KeyedMergeCursorState<T>>
- Returns:
- the weakest reason for stopping
-
getContinuationObject
@Nonnull public com.apple.foundationdb.record.provider.foundationdb.cursors.IntersectionCursorContinuation getContinuationObject()
Description copied from class:MergeCursor
Produce aRecordCursorContinuation
for this cursor. The super-class itself handles constructing the byte array continuation from this continuation. Most continuations will be based on the continuations of this cursors child cursors. These can be retrieved by callingMergeCursor.getChildContinuations()
. This will only be called afterMergeCursor.computeNextResultStates()
has completed.- Specified by:
getContinuationObject
in classMergeCursor<T,U,com.apple.foundationdb.record.provider.foundationdb.cursors.KeyedMergeCursorState<T>>
- Returns:
- a
RecordCursorContinuation
for this cursor based on the state of its child cursors
-
createCursorStates
@Nonnull protected static <T> List<com.apple.foundationdb.record.provider.foundationdb.cursors.KeyedMergeCursorState<T>> createCursorStates(@Nonnull Function<byte[],RecordCursor<T>> left, @Nonnull Function<byte[],RecordCursor<T>> right, @Nullable byte[] byteContinuation, @Nonnull Function<? super T,? extends List<Object>> comparisonKeyFunction)
-
createCursorStates
@Nonnull protected static <T> List<com.apple.foundationdb.record.provider.foundationdb.cursors.KeyedMergeCursorState<T>> createCursorStates(@Nonnull List<Function<byte[],RecordCursor<T>>> cursorFunctions, @Nullable byte[] byteContinuation, @Nonnull Function<? super T,? extends List<Object>> comparisonKeyFunction)
-
-