ModSQL
Class ColumnValue

java.lang.Object
  |
  +--ModSQL.ColumnValue

All Implemented Interfaces:

Function

public class ColumnValue

extends Object

implements Function

This object is used to retrieve the value of specific of a database table.

Author:

chris.studholme@utoronto.ca

Field Summary

protected int	column Index of column within table.
private boolean	index_checked Set to true if an index was searched for.
private boolean	indexed Set to true if this column is indexed.
private TableReader	reader TableReader managing the table we get data from.
protected int	table Index of table in TableReader.
private int	type Column type (one of java.sql.Types values).
private Object	value Value of column (valid if value_valid==true).
private boolean	value_valid Set to true if the value is valid.

Fields inherited from interface ModSQL.Function

MATCH_BEGINS, MATCH_EQU, MATCH_GT, MATCH_GTE, MATCH_LT, MATCH_LTE, MATCH_NE

Constructor Summary

ColumnValue(TableReader reader, int table, int column)
Constructor.

Method Summary

void	addParameter(Function item) Adds a parameter to the list of parameters.
Object	evaluate(boolean aggregate) Return the value of the column in the current row.
Object	evaluate(int match_op, Object match_value) Return the value of the column in the current row.
void	evaluateOrder(int index, int order) Specify the order in which the parameters should be evaluated.
int	getMaxResultSize() Return the maximum number of characters that this function expects to return in a String object.
Function	getParameter(int index) Get a particular parameter.
int	getParameterCount() Number of parameters.
int	getSQLType() Return the SQL type of the value that this function expects to return.
void	invalidate() Invalidate cached value.
boolean	isAggregate() Determine if this function will return a value that is an aggregate of many database rows.
boolean	isConstant() Determine if this function returns a constant value.
void	optimize() This implementation only sets the type variable.
void	registerWith(Object o) This method is used by the TableReader object when ordering parameters.
void	reset() Reset aggregate function.
void	setValue(Object v) Set cached value and mark the value as valid.
String	toString() Returns "table_alias.column_name".

Methods inherited from class java.lang.Object

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

Field Detail

reader

private TableReader reader

TableReader managing the table we get data from.

table

protected int table

Index of table in TableReader.

column

protected int column

Index of column within table.

index_checked

private boolean index_checked

Set to true if an index was searched for.

indexed

private boolean indexed

Set to true if this column is indexed.

value_valid

private boolean value_valid

Set to true if the value is valid.

value

private Object value

Value of column (valid if value_valid==true).

type

private int type

Column type (one of java.sql.Types values).

Constructor Detail

ColumnValue

public ColumnValue(TableReader reader,
                   int table,
                   int column)

Constructor.

Parameters:

reader - TableReader managing table

table - index of table in reader

column - index of column in table

Method Detail

getParameterCount

public int getParameterCount()

Number of parameters. ColumnValue does not support parameters so this method always returns 0.

Specified by:

getParameterCount in interface Function

Returns:

0

getParameter

public Function getParameter(int index)

Get a particular parameter. ColumnValue does not support parameters.

Specified by:

getParameter in interface Function

Parameters:

index - index of parameter to get

Returns:

parameter (function)

Throws:

IndexOutOfBoundsException - in all cases

addParameter

public void addParameter(Function item)
                  throws SQLException

Adds a parameter to the list of parameters. ColumnValue does not support parameters.

Specified by:

addParameter in interface Function

Parameters:

item - function to add

Throws:

SQLException - in all cases

evaluateOrder

public void evaluateOrder(int index,
                          int order)

Specify the order in which the parameters should be evaluated. ColumnValue does not support parameters.

Specified by:

evaluateOrder in interface Function

Parameters:

index - index of parameter

order - number indicating order in which parameter is evaluated

Throws:

IndexOutOfBoundsException - in all cases

registerWith

public void registerWith(Object o)
                  throws SQLException

This method is used by the TableReader object when ordering parameters. The TableReader object will call this method with a TableReader.TableAccess object to find out which columns are accessed by each parameter and whether those columns are indexed or not.

Objects of any other type are ignored.

Specified by:

registerWith in interface Function

Parameters:

o - object to register with

Throws:

SQLException - if an error occurs

optimize

public void optimize()
              throws SQLException

This implementation only sets the type variable.

Specified by:

optimize in interface Function

Throws:

SQLException - if an error occurs

isConstant

public boolean isConstant()

Determine if this function returns a constant value. ColumnValues are never constant.

Specified by:

isConstant in interface Function

Returns:

false

isAggregate

public boolean isAggregate()

Determine if this function will return a value that is an aggregate of many database rows. ColumnValues are never aggregate.

Specified by:

isAggregate in interface Function

Returns:

false

getSQLType

public int getSQLType()
               throws SQLException

Return the SQL type of the value that this function expects to return. The data returned by the function must either be of this type, or null.

Specified by:

getSQLType in interface Function

Returns:

SQL type of data to be returned

Throws:

SQLException - if an error occurs

getMaxResultSize

public int getMaxResultSize()
                     throws SQLException

Return the maximum number of characters that this function expects to return in a String object. If the function does not expect to return a String object or if it cannot guess a maximum value, -1 should be returned.

Specified by:

getMaxResultSize in interface Function

Returns:

maximum size of String returned or -1 if unknown

Throws:

SQLException - if an error occurs

toString

public String toString()

Returns "table_alias.column_name". If the table does not have an alias, "table_name.column_name" is returned.

Overrides:

toString in class Object

Returns:

human readable description of column

invalidate

public void invalidate()

Invalidate cached value.

setValue

public void setValue(Object v)

Set cached value and mark the value as valid.

Parameters:

v - value to set

reset

public void reset()

Reset aggregate function. This method does nothing.

Specified by:

reset in interface Function

Following copied from interface: ModSQL.Function

Throws:

SQLException - if an error occurs

evaluate

public Object evaluate(boolean aggregate)
                throws SQLException,
                       EndOfTable

Return the value of the column in the current row. If the value of the column has been cached and is valid, that value is returned. Otherwise, a value is read from the TableReader, and if the TableReader is forced to advance to the next row in the database, EndOfTable may be thrown.

If aggregate is true, an exception is thrown.

Specified by:

evaluate in interface Function

Parameters:

aggregate - true to return final aggregate value

Returns:

result object

Throws:

SQLException - if an error occurs

EndOfTable - if the end of the table is reached

evaluate

public Object evaluate(int match_op,
                       Object match_value)
                throws SQLException,
                       EndOfTable

Return the value of the column in the current row. If the value of the column has been cached and is valid, that value is returned. Otherwise, a value is read from the TableReader, and if the TableReader is forced to advance to the next row in the database, EndOfTable may be thrown.

If the TableReader is read from and match_op is MATCH_EQU, an attempt is made to find a row in the database where the column constains match_value. An index may be used to speed up this search. This method makes no guarantee that such a value can be found and may return some other value (even in cases where the desired row exists).

Specified by:

evaluate in interface Function

Parameters:

match_op - how desired value is matched

match_value - value to match to

Returns:

result object

Throws:

SQLException - if an error occurs

EndOfTable - if the end of the table is reached