Project

java.lang.Object
- simpledb.Operator
- - simpledb.Project

All Implemented Interfaces:

java.io.Serializable, DbIterator
```
public class Project
extends Operator
```
Project is an operator that implements a relational projection.

See Also:

Serialized Form

Field Summary

Fields
Modifier and Type	Field and Description
`private DbIterator`	`child`
`private java.util.ArrayList<java.lang.Integer>`	`outFieldIds`
`private static long`	`serialVersionUID`
`private TupleDesc`	`td`

Constructor Summary

Constructors
Constructor and Description
`Project(java.util.ArrayList<java.lang.Integer> fieldList, java.util.ArrayList<Type> typesList, DbIterator child)` Constructor accepts a child operator to read tuples to apply projection to and a list of fields in output tuple
`Project(java.util.ArrayList<java.lang.Integer> fieldList, Type[] types, DbIterator child)`

Method Summary

All Methods Instance Methods Concrete Methods
Modifier and Type	Method and Description
`void`	`close()` Closes this iterator.
`protected Tuple`	`fetchNext()` Operator.fetchNext implementation.
`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
  - child
```
private DbIterator child
```
  - td
```
private TupleDesc td
```
  - outFieldIds
```
private java.util.ArrayList<java.lang.Integer> outFieldIds
```
- Constructor Detail
  - Project
```
public Project(java.util.ArrayList<java.lang.Integer> fieldList,
               java.util.ArrayList<Type> typesList,
               DbIterator child)
```
    Constructor accepts a child operator to read tuples to apply projection to and a list of fields in output tuple
    
    Parameters:
    
    fieldList - The ids of the fields child's tupleDesc to project out
    
    typesList - the types of the fields in the final projection
    
    child - The child operator
  - Project
```
public Project(java.util.ArrayList<java.lang.Integer> fieldList,
               Type[] types,
               DbIterator child)
```
- 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,
                 java.util.NoSuchElementException,
                 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.
    
    java.util.NoSuchElementException
    
    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 java.util.NoSuchElementException,
                          TransactionAbortedException,
                          DbException
```
    Operator.fetchNext implementation. Iterates over tuples from the child operator, projecting out the fields from the tuple
    
    Specified by:
    
    fetchNext in class Operator
    
    Returns:
    
    The next tuple, or null if there are no more tuples
    
    Throws:
    
    java.util.NoSuchElementException
    
    TransactionAbortedException
    
    DbException
  - 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

Class Project

Field Summary

Constructor Summary

Method Summary

Methods inherited from class simpledb.Operator

Methods inherited from class java.lang.Object

Field Detail

serialVersionUID

child

td

outFieldIds

Constructor Detail

Project

Project

Method Detail

getTupleDesc

open

close

rewind

fetchNext

getChildren

setChildren