Interface ScanController
-
- All Superinterfaces:
GenericScanController
,RowCountable
- All Known Subinterfaces:
ScanControllerRowSource
,ScanManager
- All Known Implementing Classes:
B2IForwardScan
,B2IMaxScan
,BTreeForwardScan
,BTreeMaxScan
,BTreeScan
,GenericScanController
,HeapCompressScan
,HeapScan
,MergeScan
,MergeScanRowSource
,Scan
,SortBufferRowSource
,SortBufferScan
,SortScan
public interface ScanController extends GenericScanController
A scan is the mechanism for iterating over the rows in a conglomerate, the scan controller is the interface through which access clients control the underlying scan. An instance of a scan controller can be thought of as an open scan.Scans are opened from a TransactionController.
A ScanController can handle partial rows. Partial rows are described in RowUtil.
A scan controller is opened with a FormatableBitSet that describes the columns that need to be returned on a fetch call. This FormatableBitSet need not include any columns referenced in the qualifers, start and/or stop keys.- See Also:
TransactionController.openScan(long, boolean, int, int, int, org.apache.derby.iapi.services.io.FormatableBitSet, org.apache.derby.iapi.types.DataValueDescriptor[], int, org.apache.derby.iapi.store.access.Qualifier[][], org.apache.derby.iapi.types.DataValueDescriptor[], int)
,GenericScanController
,RowCountable
,RowUtil
-
-
Method Summary
All Methods Instance Methods Abstract Methods Modifier and Type Method Description boolean
delete()
Delete the row at the current position of the scan.void
didNotQualify()
A call to allow client to indicate that current row does not qualify.boolean
doesCurrentPositionQualify()
Returns true if the current position of the scan still qualifies under the set of qualifiers passed to the openScan().void
fetch(DataValueDescriptor[] destRow)
Fetch the (partial) row at the current position of the Scan.void
fetchLocation(RowLocation destRowLocation)
Fetch the location of the current position in the scan.boolean
fetchNext(DataValueDescriptor[] destRow)
Fetch the (partial) row at the next position of the Scan.void
fetchWithoutQualify(DataValueDescriptor[] destRow)
The same as fetch, except that the qualifiers passed to the openScan() will not be applied. destRow will contain the current row even if it has been changed and no longer qualifies.boolean
isCurrentPositionDeleted()
Returns true if the current position of the scan is at a deleted row.boolean
isHeldAfterCommit()
Return true is the scan has been closed after a commit, but was opened with holdability and can be reopened using positionAtRowLocation.boolean
next()
Move to the next position in the scan.boolean
positionAtRowLocation(RowLocation rl)
Positions the scan at row location and locks the row.boolean
replace(DataValueDescriptor[] row, FormatableBitSet validColumns)
Replace the (partial) row at the current position of the scan.-
Methods inherited from interface org.apache.derby.iapi.store.access.GenericScanController
close, getScanInfo, isKeyed, isTableLocked, newRowLocationTemplate, reopenScan, reopenScanByRowLocation
-
Methods inherited from interface org.apache.derby.iapi.store.access.RowCountable
getEstimatedRowCount, setEstimatedRowCount
-
-
-
-
Field Detail
-
GE
static final int GE
GE is used to position a scan at values greater than or or equal to the given key in the scan. This positioning argument refers to the order within the scan (not necessarily actual compare calls on the datatypes). "greater" than is interpreted in terms of the current conglomerate and scan. For instance, a btree may be ordered ascending on an int, in that case a 2 is "greater" than 1 in a forward scan on that index, and 1 is "greater" than 2 in a backward scan. If the btree was ordered descending on an int then 1 is "greater" than 2 in a forward scan on that index, and 2 is "greater" than 1 in a backward scan.- See Also:
TransactionController.openScan(long, boolean, int, int, int, org.apache.derby.iapi.services.io.FormatableBitSet, org.apache.derby.iapi.types.DataValueDescriptor[], int, org.apache.derby.iapi.store.access.Qualifier[][], org.apache.derby.iapi.types.DataValueDescriptor[], int)
, Constant Field Values
-
GT
static final int GT
GT is used to position a scan at values greater than the given key. This positioning argument refers to the order within the scan (not necessarily actual compare calls on the datatypes). "greater" than is interpreted in terms of the current conglomerate and scan. For instance, a btree may be ordered ascending on an int, in that case a 2 is "greater" than 1 in a forward scan on that index, and 1 is "greater" than 2 in a backward scan. If the btree was ordered descending on an int then 1 is "greater" than 2 in a forward scan on that index, and 2 is "greater" than 1 in a backward scan.- See Also:
TransactionController.openScan(long, boolean, int, int, int, org.apache.derby.iapi.services.io.FormatableBitSet, org.apache.derby.iapi.types.DataValueDescriptor[], int, org.apache.derby.iapi.store.access.Qualifier[][], org.apache.derby.iapi.types.DataValueDescriptor[], int)
, Constant Field Values
-
NA
static final int NA
NA - argument is unused in call. For some scans the key is set to null to indicate no start or stop position, in those cases the position operator is ignored.- See Also:
TransactionController.openScan(long, boolean, int, int, int, org.apache.derby.iapi.services.io.FormatableBitSet, org.apache.derby.iapi.types.DataValueDescriptor[], int, org.apache.derby.iapi.store.access.Qualifier[][], org.apache.derby.iapi.types.DataValueDescriptor[], int)
, Constant Field Values
-
-
Method Detail
-
delete
boolean delete() throws StandardException
Delete the row at the current position of the scan.- Returns:
- true if the delete was successful, false if the current position is no longer valid (ie. if it was already deleted).
- Throws:
StandardException
- Standard exception policy.
-
didNotQualify
void didNotQualify() throws StandardException
A call to allow client to indicate that current row does not qualify.Indicates to the ScanController that the current row does not qualify for the scan. If the isolation level of the scan allows, this may result in the scan releasing the lock on this row.
Note that some scan implimentations may not support releasing locks on non-qualifying rows, or may delay releasing the lock until sometime later in the scan (ie. it may be necessary to keep the lock until either the scan is repositioned on the next row or page).
This call should only be made while the scan is positioned on a current valid row.
- Throws:
StandardException
- Standard exception policy.
-
doesCurrentPositionQualify
boolean doesCurrentPositionQualify() throws StandardException
Returns true if the current position of the scan still qualifies under the set of qualifiers passed to the openScan(). When called this routine will reapply all qualifiers against the row currently positioned and return true if the row still qualifies. If the row has been deleted or no longer passes the qualifiers then this routine will return false. This case can come about if the current scan or another scan on the same table in the same transaction deleted the row or changed columns referenced by the qualifier after the next() call which positioned the scan at this row. Note that for comglomerates which don't support update, like btree's, there is no need to recheck the qualifiers. The results of a fetch() performed on a scan positioned on a deleted row are undefined, note that this can happen even if next() has returned true (for instance the client can delete the row, or if using read uncommitted another thread can delete the row after the next() call but before the fetch).- Throws:
StandardException
- Standard exception policy.
-
isHeldAfterCommit
boolean isHeldAfterCommit() throws StandardException
Return true is the scan has been closed after a commit, but was opened with holdability and can be reopened using positionAtRowLocation.- Throws:
StandardException
- Standard exception policy.- See Also:
positionAtRowLocation(org.apache.derby.iapi.types.RowLocation)
-
fetch
void fetch(DataValueDescriptor[] destRow) throws StandardException
Fetch the (partial) row at the current position of the Scan. The value in the destRow storable row is replaced with the value of the row at the current scan position. The columns of the destRow row must be of the same type as the actual columns in the underlying conglomerate. The number of elements in fetch must be compatible with the number of scan columns requested at the openScan call time.
A fetch can return a sub-set of the scan columns requested at scan open time by supplying a destRow will less elements than the number of requested columns. In this case the N leftmost of the requested columns are fetched, where N = destRow.length. In the case where all columns are rested and N = 2 then columns 0 and 1 are returned. In the case where the openScan FormatableBitSet requested columns 1, 4 and 7, then columns 1 and 4 would be fetched when N = 2.
The results of a fetch() performed on a scan after next() has returned false are undefined. A fetch() performed on a scan positioned on a deleted row will throw a StandardException with state = SQLState.AM_RECORD_NOT_FOUND. Note that this can happen even if next() has returned true (for instance the client can delete the row, or if using read uncommitted another thread can delete the row after the next() call but before the fetch).- Parameters:
destRow
- The row into which the value of the current position in the scan is to be stored.- Throws:
StandardException
- Standard exception policy.- See Also:
RowUtil
-
fetchWithoutQualify
void fetchWithoutQualify(DataValueDescriptor[] destRow) throws StandardException
The same as fetch, except that the qualifiers passed to the openScan() will not be applied. destRow will contain the current row even if it has been changed and no longer qualifies.- Parameters:
destRow
- The row into which the value of the current position in the scan is to be stored.- Throws:
StandardException
- Standard exception policy.
-
fetchNext
boolean fetchNext(DataValueDescriptor[] destRow) throws StandardException
Fetch the (partial) row at the next position of the Scan. If there is a valid next position in the scan then the value in the destRow storable row is replaced with the value of the row at the current scan position. The columns of the destRow row must be of the same type as the actual columns in the underlying conglomerate. The resulting contents of destRow after a fetchNext() which returns false is undefined. The result of calling fetchNext(row) is exactly logically equivalent to making a next() call followed by a fetch(row) call. This interface allows implementations to optimize the 2 calls if possible.- Parameters:
destRow
- The destRow row into which the value of the next position in the scan is to be stored.- Returns:
- True if there is a next position in the scan, false if there isn't.
- Throws:
StandardException
- Standard exception policy.- See Also:
fetch(org.apache.derby.iapi.types.DataValueDescriptor[])
,RowUtil
-
fetchLocation
void fetchLocation(RowLocation destRowLocation) throws StandardException
Fetch the location of the current position in the scan. The destination location is replaced with the location corresponding to the current position in the scan. The destination location must be of the correct actual type to accept a location from the underlying conglomerate location. The results of a fetchLocation() performed on a scan after next() has returned false are undefined. The results of a fetchLocation() performed on a scan positioned on a deleted row are undefined, note that this can happen even if next() has returned true (for instance the client can delete the row, or if using read uncommitted another thread can delete the row after the next() call but before the fetchLocation).- Throws:
StandardException
- Standard exception policy.
-
isCurrentPositionDeleted
boolean isCurrentPositionDeleted() throws StandardException
Returns true if the current position of the scan is at a deleted row. This case can come about if the current scan or another scan on the same table in the same transaction deleted the row after the next() call which positioned the scan at this row. The results of a fetch() performed on a scan positioned on a deleted row are undefined.- Throws:
StandardException
- Standard exception policy.
-
next
boolean next() throws StandardException
Move to the next position in the scan. If this is the first call to next(), the position is set to the first row. Returns false if there is not a next row to move to. It is possible, but not guaranteed, that this method could return true again, after returning false, if some other operation in the same transaction appended a row to the underlying conglomerate.- Returns:
- True if there is a next position in the scan, false if there isn't.
- Throws:
StandardException
- Standard exception policy.
-
positionAtRowLocation
boolean positionAtRowLocation(RowLocation rl) throws StandardException
Positions the scan at row location and locks the row. If the scan is not opened, it will be reopened if this is a holdable scan and there has not been any operations which causes RowLocations to be invalidated.- Parameters:
rl
- RowLocation for the new position for the scan. The RowLocation submitted should be a RowLocation which has previously been returned by this ScanController.- Returns:
- true if the scan has been positioned at the RowLocation. false if the scan could not be positioned.
- Throws:
StandardException
- Standard exception policy.
-
replace
boolean replace(DataValueDescriptor[] row, FormatableBitSet validColumns) throws StandardException
Replace the (partial) row at the current position of the scan.- Returns:
- true if the replace was successful, false if the current position is no longer valid (ie. if it was deleted).
- Throws:
StandardException
- Standard exception policy.- See Also:
RowUtil
-
-