FileScanOperator Class Reference

Sample implementation of a record file scan operator. More...

#include <FileScanOperator.h>

Inherits IScanOperator.

List of all members.

Public Member Functions
	FileScanOperator (const char *relation, int nAttributes, const RelationAttributeInfo attributes[])
ReturnCode	openExecution ()
	Notifies the operator that query execution is about to begin.
ReturnCode	closeExecution ()
	Notifies the operator that query execution has completed.
ReturnCode	getNextRecord (Record *record)
	Gets the next record.
int	getArity ()
	Gets the number of attributes of this operator.
void	getSchema (RelationAttributeInfo attributes[])
	Gets the list of attributes of this operator.
void	printSubtree (int indent)
	Prints this operator and its subtree.
ReturnCode	openScan (int nAttribute, ComparisonOp op, const TypedValue *value)
	Opens a scan with a given comparison operator and value.
ReturnCode	closeScan ()
	Closes the scan, performing any necessary cleanup.

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Detailed Description

Sample implementation of a record file scan operator.

Sample implementation of a record file scan operator. You are free to use the class as is, change it as you see fit, or ignore it completely.

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Member Function Documentation

ReturnCode FileScanOperator::openExecution

(

)

[virtual]

Notifies the operator that query execution is about to begin.

This method is intended to be invoked once, before the first invocation of getNextRecord, to give the operator implementation a chance to perform any necessary initialization before query execution gets underway. The operator should call openExecution on any children when this method is invoked, even if it does nothing else. Returns RC_OK on success, and other error codes on failure.

Implements IQueryOperator.

ReturnCode FileScanOperator::closeExecution

(

)

[virtual]

Notifies the operator that query execution has completed.

This method is intended to be invoked once, after the last invocation of getNextRecord, to signal to the operator that query execution has completed (so that any necessary cleanup can be performed). The operator should call closeExecution on any children when this method is invoked, even if it does nothing else.

Implements IQueryOperator.

ReturnCode FileScanOperator::getNextRecord

(

Record *

record

)

[virtual]

Gets the next record.

Parameters:

record

Record object to hold the returned record

This method is called each time the parent operator requires another record. The intention is that at the top level, QueryEngine invokes getNextRecord repeatedly on the root operator in the tree to retrieve the answers to a query. Each operator will in turn call getNextRecord on its children, while performing whatever operator-specific processing of those records is required. At the bottom of the tree, file scan or index scan operators return records from disk in their getNextRecord implementations. Returns RC_OK on success, RC_EOF if there are no more records, and other RC error codes otherwise.

The record parameter is managed by the caller, who must ensure that it is the right size returned records. (The buffer must be at least recordSize in length, where recordSize is the sum of the lengths of the attributes of this operator.)

The rationale for using a Record object, rather than simply a data buffer, is to support query plans involving updates (where the operator at the top of the execution plan needs to know the RecordID of a record matching the specified selection conditions). Unary operators, such as projection and selection, should probably preserve the RecordID of tuples passing up through them. For binary operators such as join, the returned RecordID is not meaningful and may be arbitrary.

Implements IQueryOperator.

int FileScanOperator::getArity

(

)

[virtual]

Gets the number of attributes of this operator.

Returns the number of attributes in records returned by this operator

Implements IQueryOperator.

void FileScanOperator::getSchema

(

RelationAttributeInfo

attributes[]

)

[virtual]

Gets the list of attributes of this operator.

Parameters:

attributes

The list of attributes to be filled in

Gets the list of attributes of this operator. The attributes array is managed by the caller and must be of length equal to getArity().

Implements IQueryOperator.

void FileScanOperator::printSubtree

(

int

indent

)

[virtual]

Prints this operator and its subtree.

Parameters:

indent

The level of indentation

Prints this operator and its subtree to standard output. This is an optional method that you may find useful to implement for debugging purposes. It should print whatever information is deemed relevant, then call printSubtree for each child node with an incremented indent parameter.

Implements IQueryOperator.

ReturnCode FileScanOperator::openScan	(	int	nAttribute,
		ComparisonOp	op,
		const TypedValue *	value
	)			[virtual]

Opens a scan with a given comparison operator and value.

Parameters:

	nAttribute	Which column is to be used in the comparison
	op	The comparison being performed
	value	The constant value being compared against

Opens a scan with a given comparison operator and value. For each tuple obtained from the left child of the NestedLoopsJoinOperator, openScan will be called on the right child with the value taken from the tuple.

Implements IScanOperator.

ReturnCode FileScanOperator::closeScan

(

)

[virtual]

Closes the scan, performing any necessary cleanup.

Closes the scan, performing any necessary cleanup.

Implements IScanOperator.

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The documentation for this class was generated from the following files:

• FileScanOperator.h
• FileScanOperator.cpp