simpledb

Class Delete

java.lang.Object

simpledb.Operator

simpledb.Delete

All Implemented Interfaces:

java.io.Serializable, DbIterator

public class Delete
extends Operator

The delete operator. Delete reads tuples from its child operator and removes them from the table they belong to.

See Also:

Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
private static long	serialVersionUID

Constructor Summary

Constructors

Constructor and Description
Delete(TransactionId t, DbIterator child) Constructor specifying the transaction that this delete belongs to as well as the child to read from.

Method Summary

Methods

Modifier and Type	Method and Description
void	close() Closes this iterator.
protected Tuple	fetchNext() Deletes tuples as they are read from the child operator.
DbIterator[]	getChildren()
TupleDesc	getTupleDesc() Returns the TupleDesc associated with this DbIterator.
void	open() Opens the iterator.
void	rewind() Resets the iterator to the start.
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

Constructor Detail

Delete

public Delete(TransactionId t,
      DbIterator child)

Constructor specifying the transaction that this delete belongs to as well as the child to read from.

Parameters:

t - The transaction this delete runs in

child - The child operator from which to read tuples for deletion

Method Detail

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:

return the TupleDesc of the output tuples of this operator

open

public void open()
          throws DbException,
                 TransactionAbortedException

Description copied from interface: DbIterator

Opens the iterator. This must be called before any of the other methods.

Specified by:

open in interface DbIterator

Overrides:

open in class Operator

Throws:

DbException - when there are problems opening/accessing the database.

TransactionAbortedException

close

public void close()

Description copied from class: Operator

Closes this iterator. If overridden by a subclass, they should call super.close() in order for Operator's internal state to be consistent.

Specified by:

close in interface DbIterator

Overrides:

close in class Operator

rewind

public void rewind()
            throws DbException,
                   TransactionAbortedException

Description copied from interface: DbIterator

Resets the iterator to the start.

Throws:

DbException - when rewind is unsupported.

TransactionAbortedException

fetchNext

protected Tuple fetchNext()
                   throws TransactionAbortedException,
                          DbException

Deletes tuples as they are read from the child operator. Deletes are processed via the buffer pool (which can be accessed via the Database.getBufferPool() method.

Specified by:

fetchNext in class Operator

Returns:

A 1-field tuple containing the number of deleted records.

Throws:

TransactionAbortedException

DbException

See Also:

Database.getBufferPool(), BufferPool.deleteTuple(simpledb.TransactionId, 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)

Description copied from class: Operator

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