org.vanilladb.core.query.algebra

Class SelectScan

java.lang.Object

org.vanilladb.core.query.algebra.SelectScan

All Implemented Interfaces:

Scan, UpdateScan, Record

public class SelectScan
extends Object
implements UpdateScan

The scan class corresponding to the select relational algebra operator. All methods except next delegate their work to the underlying scan.

Constructor Summary

Constructors

Constructor and Description
SelectScan(Scan s, Predicate pred) Creates a select scan having the specified underlying scan and predicate.

Method Summary

Modifier and Type	Method and Description
void	beforeFirst() Positions the scan before its first record.
void	close() Closes the scan and its subscans, if any.
void	delete() Deletes the current record from the scan.
RecordId	getRecordId() Returns the RecordId of the current record.
Constant	getVal(String fldName) Returns the value of the specified field.
boolean	hasField(String fldName) Returns true if the scan has the specified field.
void	insert() Inserts a new record somewhere in the scan.
void	moveToRecordId(RecordId rid) Positions the scan so that the current record has the specified record ID .
boolean	next() Move to the next record satisfying the predicate.
void	setVal(String fldname, Constant val) Modifies the field value of the current record.

Methods inherited from class java.lang.Object

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

Constructor Detail

SelectScan

public SelectScan(Scan s,
                  Predicate pred)

Creates a select scan having the specified underlying scan and predicate.

Parameters:

s - the scan of the underlying query

pred - the selection predicate

Method Detail

beforeFirst

public void beforeFirst()

Description copied from interface: Scan

Positions the scan before its first record.

Specified by:

beforeFirst in interface Scan

next

public boolean next()

Move to the next record satisfying the predicate. The method repeatedly calls next on the underlying scan until a suitable record is found, or the underlying scan contains no more records.

Specified by:

next in interface Scan

Returns:

false if there is no next record

See Also:

Scan.next()

close

public void close()

Description copied from interface: Scan

Closes the scan and its subscans, if any.

Specified by:

close in interface Scan

getVal

public Constant getVal(String fldName)

Description copied from interface: Record

Returns the value of the specified field.

Specified by:

getVal in interface Record

Parameters:

fldName - the name of the field

Returns:

the value of that field

hasField

public boolean hasField(String fldName)

Description copied from interface: Scan

Returns true if the scan has the specified field.

Specified by:

hasField in interface Scan

Parameters:

fldName - the name of the field

Returns:

true if the scan has that field

setVal

public void setVal(String fldname,
                   Constant val)

Description copied from interface: UpdateScan

Modifies the field value of the current record.

Specified by:

setVal in interface UpdateScan

Parameters:

fldname - the name of the field

val - the new value, expressed as a Constant

delete

public void delete()

Description copied from interface: UpdateScan

Deletes the current record from the scan.

Specified by:

delete in interface UpdateScan

insert

public void insert()

Description copied from interface: UpdateScan

Inserts a new record somewhere in the scan.

Specified by:

insert in interface UpdateScan

getRecordId

public RecordId getRecordId()

Description copied from interface: UpdateScan

Returns the RecordId of the current record.

Specified by:

getRecordId in interface UpdateScan

Returns:

the RecordId of the current record

moveToRecordId

public void moveToRecordId(RecordId rid)

Description copied from interface: UpdateScan

Positions the scan so that the current record has the specified record ID .

Specified by:

moveToRecordId in interface UpdateScan

Parameters:

rid - the RecordId of the desired record