ModSQL
Class IndirectFunction

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

All Implemented Interfaces:

Function

final class IndirectFunction

extends Object

implements Function

Wrapper for some other function. This class is typically used to hold column names before the names can be looked up. It may also be used to make a function appear in two seperate locations (such as SELECT expressions appearing in the ORDER BY clause).

Author:

chris.studholme@utoronto.ca

Field Summary

private String	description Text description of function (usually a column name).
private boolean	force_aggregate Make the function appear as an aggregate regardless of whether it is or not (used for GROUP BY columns).
private Object	last_value Last value returned by function (used for forced aggregates).
private Function	value Function being wrapped.

Fields inherited from interface ModSQL.Function

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

Constructor Summary

IndirectFunction(String description)
Constructor.

Method Summary

void	addParameter(Function item) Adds a parameter to the list of parameters.
Object	evaluate(boolean aggregate) Evaluate the function and return the result.
Object	evaluate(int match_op, Object match_value) Calls the equivalent evaluate() method for the underlying function.
void	evaluateOrder(int index, int order) Specify the order in which the parameters should be evaluated.
String	getDescription() Get text description of function.
Function	getFunction() Get function being wrapped.
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() Get the number of parameters.
int	getSQLType() Return the SQL type of the value that this function expects to return.
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() If the function has been set, it is optimized.
void	registerWith(Object o) This method responds to two objects: FunctionProvider to lookup the description if the function has not been set yet, and Select.GroupByList to check for GROUP BY columns that need to be forced to aggregate.
void	reset() Calls reset() for the underlying function and set the last value returned by evaluate() to null.
String	toString() Returns string version of function or description if function is not set yet.

Methods inherited from class java.lang.Object

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

Field Detail

description

private String description

Text description of function (usually a column name).

value

private Function value

Function being wrapped.

force_aggregate

private boolean force_aggregate

Make the function appear as an aggregate regardless of whether it is or not (used for GROUP BY columns).

last_value

private Object last_value

Last value returned by function (used for forced aggregates).

Constructor Detail

IndirectFunction

public IndirectFunction(String description)

Constructor.

Parameters:

description - text description of function (column name)

Method Detail

toString

public String toString()

Returns string version of function or description if function is not set yet.

Overrides:

toString in class Object

Returns:

human readable description of function

getDescription

public String getDescription()

Get text description of function.

Returns:

text description of function

getFunction

public Function getFunction()

Get function being wrapped.

Returns:

function being wrapped (null if not set)

getParameterCount

public int getParameterCount()

Get the number of parameters. Returns 0 as parameters cannot be indirectly accessed.

Specified by:

getParameterCount in interface Function

Returns:

number of parameters

getParameter

public Function getParameter(int index)

Get a particular parameter. Throws an exception as parameters cannot be indirectly accessed.

Specified by:

getParameter in interface Function

Parameters:

index - index of parameter to get

Returns:

parameter (function)

Throws:

IndexOutOfBoundsException - always

addParameter

public void addParameter(Function item)
                  throws SQLException

Adds a parameter to the list of parameters. Throws an exception as parameters cannot be indirectly accessed.

Specified by:

addParameter in interface Function

Parameters:

item - function to add

Throws:

SQLException - always

evaluateOrder

public void evaluateOrder(int index,
                          int order)

Specify the order in which the parameters should be evaluated. Throws an exception as parameters cannot be indirectly accessed.

Specified by:

evaluateOrder in interface Function

Parameters:

index - index of parameter

order - number indicating order in which parameter is evaluated

Throws:

IndexOutOfBoundsException - always

registerWith

public void registerWith(Object o)
                  throws SQLException

This method responds to two objects:

• FunctionProvider to lookup the description if the function has not been set yet, and
• Select.GroupByList to check for GROUP BY columns that need to be forced to aggregate.

Otherwise, if the function has been set, the object is passed on to that function.

Specified by:

registerWith in interface Function

Parameters:

o - object to register with

Throws:

SQLException - if an error occurs

optimize

public void optimize()
              throws SQLException

If the function has been set, it is optimized. Otherwise, an exception is thrown.

Specified by:

optimize in interface Function

Throws:

SQLException - if an error occurs

isConstant

public boolean isConstant()
                   throws SQLException

Determine if this function returns a constant value.

Specified by:

isConstant in interface Function

Returns:

true if the value returned is constant

Throws:

SQLException - if an error occurs

isAggregate

public boolean isAggregate()
                    throws SQLException

Determine if this function will return a value that is an aggregate of many database rows. This method may return true in cases where the function is actually not an aggregate (in this case, aggregate has been forced).

Specified by:

isAggregate in interface Function

Returns:

true if the function aggregates several rows of data

Throws:

SQLException - if an error occurs

getSQLType

public int getSQLType()
               throws SQLException

Return the SQL type of the value that this function expects to return.

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.

Specified by:

getMaxResultSize in interface Function

Returns:

maximum size of String returned or -1 if unknown

Throws:

SQLException - if an error occurs

evaluate

public Object evaluate(boolean aggregate)
                throws SQLException,
                       EndOfTable

Evaluate the function and return the result. If aggregate is true, but the function is not an aggregate and aggregate is being forced, the last value returned by evaluate is returned again. In this case, if evaluate() has never been called, null is returned.

Specified by:

evaluate in interface Function

Parameters:

aggregate - true to get final aggregate value

Returns:

result object

Throws:

SQLException - if an error occurs

EndOfTable - if thrown by the function

evaluate

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

Calls the equivalent evaluate() method for the underlying function.

Specified by:

evaluate in interface Function

Parameters:

match_op - how the value should be matched

match_value - desired value

Returns:

result object

Throws:

SQLException - if an error occurs

EndOfTable - if thrown by the function

reset

public void reset()
           throws SQLException

Calls reset() for the underlying function and set the last value returned by evaluate() to null.

Specified by:

reset in interface Function

Throws:

SQLException - if an error occurs