simpledb

Class Filter

java.lang.Object

simpledb.Operator

simpledb.Filter

All Implemented Interfaces:

java.io.Serializable, DbIterator

public class Filter
extends Operator

Filter is an operator that implements a relational select.

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
private DbIterator	iterator
private Predicate	predicate
private static long	serialVersionUID

Constructor Summary

Constructors

Constructor and Description
Filter(Predicate p, DbIterator child) Constructor accepts a predicate to apply and a child operator to read tuples to filter from.

Method Summary

Modifier and Type	Method and Description
void	close() Closes the iterator
protected Tuple	fetchNext() AbstractDbIterator.readNext implementation.
DbIterator[]	getChildren()
Predicate	getPredicate()
TupleDesc	getTupleDesc() Returns the TupleDesc associated with this DbIterator.
void	open() Opens the iterator for scanning
void	rewind() Rewinds the iterator
void	setChildren(DbIterator[] children) Set the children(child) of this operator.

Methods inherited from class simpledb.Operator

getEstimatedCardinality, hasNext, next, setEstimatedCardinality

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

predicate

private Predicate predicate

iterator

private DbIterator iterator

Constructor Detail

Filter

public Filter(Predicate p,
              DbIterator child)

Constructor accepts a predicate to apply and a child operator to read tuples to filter from.

Parameters:

p - The predicate to filter tuples with

child - The child operator

Method Detail

getPredicate

public Predicate getPredicate()

Returns:

Predicate

getTupleDesc

public TupleDesc getTupleDesc()

Description copied from interface: DbIterator

Returns the TupleDesc associated with this DbIterator.

Specified by:

getTupleDesc in interface DbIterator

Specified by:

getTupleDesc in class Operator

Returns:

The tuple descriptor of the tuples

open

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

Opens the iterator for scanning

Specified by:

open in interface DbIterator

Overrides:

open in class Operator

Throws:

DbException

java.util.NoSuchElementException

TransactionAbortedException

close

public void close()

Closes the iterator

Specified by:

close in interface DbIterator

Overrides:

close in class Operator

rewind

public void rewind()
            throws DbException,
                   TransactionAbortedException

Rewinds the iterator

Throws:

DbException

TransactionAbortedException

fetchNext

protected Tuple fetchNext()
                   throws java.util.NoSuchElementException,
                          TransactionAbortedException,
                          DbException

AbstractDbIterator.readNext implementation. Iterates over tuples from the child operator, applying the predicate to them and returning those that pass the predicate (i.e. for which the Predicate.filter() returns true.)

Specified by:

fetchNext in class Operator

Returns:

The next tuple that passes the filter, or null if there are no more tuples

Throws:

java.util.NoSuchElementException

TransactionAbortedException

DbException

See Also:

Predicate.filter(simpledb.Tuple)

getChildren

public DbIterator[] getChildren()

Specified by:

getChildren in class Operator

Returns:

return the children DbIterators of this operator. If there is only one child, return an array of only one element. For join operators, the order of the children is not important. But they should be consistent among multiple calls.

setChildren

public void setChildren(DbIterator[] children)

Set the children(child) of this operator. If the operator has only one child, children[0] should be used. If the operator is a join, children[0] and children[1] should be used.

Specified by:

setChildren in class Operator

Parameters:

children - the DbIterators which are to be set as the children(child) of this operator