org.vanilladb.core.query.algebra

Class ProjectScan

java.lang.Object

org.vanilladb.core.query.algebra.ProjectScan

All Implemented Interfaces:

Scan, Record

public class ProjectScan
extends Object
implements Scan

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

Constructor Summary

Constructors

Constructor and Description
ProjectScan(Scan s, Collection<String> fieldList) Creates a project scan having the specified underlying scan and field list.

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.
Constant	getVal(String fldName) Returns the value of the specified field.
boolean	hasField(String fldName) Returns true if the specified field is in the projection list.
boolean	next() Moves the scan to the next record.

Methods inherited from class java.lang.Object

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

Constructor Detail

ProjectScan

public ProjectScan(Scan s,
                   Collection<String> fieldList)

Creates a project scan having the specified underlying scan and field list.

Parameters:

s - the underlying scan

fieldList - the list of field names

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()

Description copied from interface: Scan

Moves the scan to the next record.

Specified by:

next in interface Scan

Returns:

false if there is no next record

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)

Returns true if the specified field is in the projection list.

Specified by:

hasField in interface Scan

Parameters:

fldName - the name of the field

Returns:

true if the scan has that field

See Also:

Scan.hasField(java.lang.String)