simpledb

Class SeqScan

java.lang.Object

simpledb.SeqScan

All Implemented Interfaces:

java.io.Serializable, DbIterator

public class SeqScan
extends java.lang.Object
implements DbIterator

SeqScan is an implementation of a sequential scan access method that reads each tuple of a table in no particular order (e.g., as they are laid out on disk).

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
private DbFileIterator	iterator
private static long	serialVersionUID
private java.lang.String	tableAlias
private int	tableId
private TransactionId	tid

Constructor Summary

Constructors

Constructor and Description
SeqScan(TransactionId tid, int tableid)
SeqScan(TransactionId tid, int tableid, java.lang.String tableAlias) Creates a sequential scan over the specified table as a part of the specified transaction.

Method Summary

Modifier and Type	Method and Description
void	close() Closes the iterator
java.lang.String	getAlias()
java.lang.String	getTableName()
TupleDesc	getTupleDesc() Returns the TupleDesc with field names from the underlying HeapFile, prefixed with the tableAlias string from the constructor.
boolean	hasNext() Returns true if the iterator still has tuples
Tuple	next() Return next tuple in the iterator
void	open() Opens the Scanner for reading
void	reset(int tableid, java.lang.String tableAlias) Reset the tableid, and tableAlias of this operator.
void	rewind() Rewinds the iterator to the start

Methods inherited from class java.lang.Object

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

Field Detail

serialVersionUID

private static final long serialVersionUID

See Also:

Constant Field Values

tid

private TransactionId tid

tableId

private int tableId

tableAlias

private java.lang.String tableAlias

iterator

private DbFileIterator iterator

Constructor Detail

SeqScan

public SeqScan(TransactionId tid,
               int tableid,
               java.lang.String tableAlias)

Creates a sequential scan over the specified table as a part of the specified transaction.

Parameters:

tid - The transaction this scan is running as a part of.

tableid - the table to scan.

tableAlias - the alias of this table (needed by the parser); the returned tupleDesc should have fields with name tableAlias.fieldName (note: this class is not responsible for handling a case where tableAlias or fieldName are null. It shouldn't crash if they are, but the resulting name can be null.fieldName, tableAlias.null, or null.null).

SeqScan

public SeqScan(TransactionId tid,
               int tableid)

Method Detail

getTableName

public java.lang.String getTableName()

Returns:

return the table name of the table the operator scans. This should be the actual name of the table in the catalog of the database

getAlias

public java.lang.String getAlias()

Returns:

Return the alias of the table this operator scans.

reset

public void reset(int tableid,
                  java.lang.String tableAlias)

Reset the tableid, and tableAlias of this operator.

Parameters:

tableid - the table to scan.

tableAlias - the alias of this table (needed by the parser); the returned tupleDesc should have fields with name tableAlias.fieldName (note: this class is not responsible for handling a case where tableAlias or fieldName are null. It shouldn't crash if they are, but the resulting name can be null.fieldName, tableAlias.null, or null.null).

open

public void open()
          throws DbException,
                 TransactionAbortedException

Opens the Scanner for reading

Specified by:

open in interface DbIterator

Throws:

DbException

TransactionAbortedException

getTupleDesc

public TupleDesc getTupleDesc()

Returns the TupleDesc with field names from the underlying HeapFile, prefixed with the tableAlias string from the constructor. This prefix becomes useful when joining tables containing a field(s) with the same name.

Specified by:

getTupleDesc in interface DbIterator

Returns:

the TupleDesc with field names from the underlying HeapFile, prefixed with the tableAlias string from the constructor.

hasNext

public boolean hasNext()
                throws TransactionAbortedException,
                       DbException

Returns true if the iterator still has tuples

Specified by:

hasNext in interface DbIterator

Returns:

boolean

Throws:

TransactionAbortedException

DbException

next

public Tuple next()
           throws java.util.NoSuchElementException,
                  TransactionAbortedException,
                  DbException

Return next tuple in the iterator

Specified by:

next in interface DbIterator

Returns:

Tuple

Throws:

java.util.NoSuchElementException

TransactionAbortedException

DbException

close

public void close()

Closes the iterator

Specified by:

close in interface DbIterator

rewind

public void rewind()
            throws DbException,
                   java.util.NoSuchElementException,
                   TransactionAbortedException

Rewinds the iterator to the start

Specified by:

rewind in interface DbIterator

Throws:

DbException

java.util.NoSuchElementException

TransactionAbortedException