ModSQL
Class AbstractFunction

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

All Implemented Interfaces:

Function

Direct Known Subclasses:

AbstractAggregate, Function_Math, Function_NVL, Function_String, LiteralRow, Operator

public abstract class AbstractFunction

extends Object

implements Function

Abstract implementation of Function to simplify the implementation of real functions.

Author:

chris.studholme@utoronto.ca

Field Summary

protected boolean	all_constant Are all parameters constant?
protected boolean	constant_non_null Are all of the constant parameters non-null?
protected int[]	evaluate_order Order in which to evaluate parameters.
protected ArrayList	evaluate_order_array Parameter ordering before optimize.
protected boolean	out_of_order Are the parameters out-of-order? Used by toString().
protected boolean[]	parameter_constant Array to keep track of which parameters are constant.
protected Object[]	parameter_value Array for storing parameter values (constant or otherwise).
protected Function[]	parameters Array of parameters after optimize.
protected ArrayList	parameters_array Array of parameters before optimize.

Fields inherited from interface ModSQL.Function

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

Constructor Summary

AbstractFunction()
Default constructor.

Method Summary

void	addParameter(Function item) Adds a parameter to the list of parameters maintained by this function.
static Object	convertToSQLType(Object o, int type) Convert an Object to a compatible Object corresponding to the provided SQL type.
Object	evaluate(int match_op, Object match_value) Default implementation that simply calls evaluate(false).
boolean	evaluateConstantParameters() Evaluate parameters that advertise themselves as constant.
void	evaluateOrder(int index, int order) Specify the order in which the parameters should be evaluated.
protected boolean	evaluateParameters(boolean aggregate) Same as above version, but with stop_at_null set to false.
protected boolean	evaluateParameters(boolean aggregate, boolean stop_at_null) Evaluates all parameters and stores the results in the parameter_value array.
abstract String	functionName() Returns the name of this function for use by the toString() method.
static int	getCompatableType(int t1, int t2) Determine a java.sql.Types type that is compatable with both of the passed parameters.
static int	getObjectSQLType(Object o) Determine the SQL type of a java Object.
Function	getParameter(int index) Get a particular parameter.
int	getParameterCount() Get the number of parameters currently supplied to this function.
boolean	isAggregate() The implementation of this method is intended to be used by non-aggregate functions.
boolean	isConstant() Determine if this function returns a constant value.
void	optimize() This method sets up static arrays for the parameters and their values, calls optimize() for each parameter, and initializes the evalute_order array to appropriate values (using information provided using evaluateOrder(), if any).
String	postfixParameters() Optional String to insert after parameter list in toString().
String	prefixParameters() Optional String to insert before parameter list in toString().
void	registerWith(Object o) This implementation simply calls registerWith() for all parameters.
void	reset() This implementation simply calls reset() for all parameters and is intended to be used by non-aggregate functions.
String	toString() Outputs "functionName(parameter,...)".

Methods inherited from class java.lang.Object

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

Methods inherited from interface ModSQL.Function

evaluate, getMaxResultSize, getSQLType

Field Detail

parameters_array

protected ArrayList parameters_array

Array of parameters before optimize.

evaluate_order_array

protected ArrayList evaluate_order_array

Parameter ordering before optimize.

parameters

protected Function[] parameters

Array of parameters after optimize.

parameter_value

protected Object[] parameter_value

Array for storing parameter values (constant or otherwise).

parameter_constant

protected boolean[] parameter_constant

Array to keep track of which parameters are constant.

all_constant

protected boolean all_constant

Are all parameters constant?

constant_non_null

protected boolean constant_non_null

Are all of the constant parameters non-null?

evaluate_order

protected int[] evaluate_order

Order in which to evaluate parameters. Each entry is an index into the parameters array.

out_of_order

protected boolean out_of_order

Are the parameters out-of-order? Used by toString().

Constructor Detail

AbstractFunction

public AbstractFunction()

Default constructor. Initializes pre-optimize arrays.

Method Detail

getParameterCount

public int getParameterCount()

Get the number of parameters currently supplied to this function.

Specified by:

getParameterCount in interface Function

Returns:

number of parameters

getParameter

public Function getParameter(int index)

Get a particular parameter.

Specified by:

getParameter in interface Function

Parameters:

index - index of parameter to get

Returns:

parameter (function)

addParameter

public void addParameter(Function item)
                  throws SQLException

Adds a parameter to the list of parameters maintained by this function.

Specified by:

addParameter in interface Function

Parameters:

item - function to add

Throws:

SQLException - if optimize has already been called

evaluateOrder

public void evaluateOrder(int index,
                          int order)
                   throws SQLException

Specify the order in which the parameters should be evaluated.

Specified by:

evaluateOrder in interface Function

Parameters:

index - index of parameter

order - number indicating order in which parameter is evaluated

Throws:

SQLException - if optimize has already been called

registerWith

public void registerWith(Object o)
                  throws SQLException

This implementation simply calls registerWith() for all parameters.

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 method sets up static arrays for the parameters and their values, calls optimize() for each parameter, and initializes the evalute_order array to appropriate values (using information provided using evaluateOrder(), if any).

The all_constant variable is initialized to true if and only if the number of parameters is 0. The constant_non_null variable is initialized to true. The parameter_constant array is not initialized. Use evaluateConstantParameters() after optimize() to initialize these variables to more useful values.

Specified by:

optimize in interface Function

Throws:

SQLException - if an error occurs

evaluateConstantParameters

public boolean evaluateConstantParameters()
                                   throws SQLException

Evaluate parameters that advertise themselves as constant. This method initializes the parameter_constant, all_constant, and constant_non_null variables to their correct values.

This method may only be used after optimize() has been called. Typically, a class that overrides optimize() will first call super.optimize() and then use this method later within their new optimize() implementation.

Returns:

true if all constant parameters were non-null

Throws:

SQLException - if an error occurs while evaluating a parameter

functionName

public abstract String functionName()

Returns the name of this function for use by the toString() method.

Returns:

name of function

prefixParameters

public String prefixParameters()

Optional String to insert before parameter list in toString(). This method is used by AbstractAggregate to insert DISTINCT or "*" as needed. The default implementation returns the empty string.

postfixParameters

public String postfixParameters()

Optional String to insert after parameter list in toString(). This method is used by Operator_In to add the table expression as the second parameter. If a comma is needed to seperate the parameter list from this postfix, this method is expected to include the initial comma. The default implementation returns the empty string.

toString

public String toString()

Outputs "functionName(parameter,...)".

Overrides:

toString in class Object

Returns:

user-readable function declaration

isConstant

public boolean isConstant()
                   throws SQLException

Determine if this function returns a constant value. If all of the functions parameters are constant, then the function is considered constant as well.

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

The implementation of this method is intended to be used by non-aggregate functions. Aggregate functions should extend AbstractAggregate instead of AbstractFunction. This implementation will return true if and only if all of the function's parameters are either aggregate or constant.

Specified by:

isAggregate in interface Function

Returns:

true if the function aggregates several rows of data

Throws:

SQLException - if an error occurs

evaluateParameters

protected boolean evaluateParameters(boolean aggregate,
                                     boolean stop_at_null)
                              throws SQLException,
                                     EndOfTable

Evaluates all parameters and stores the results in the parameter_value array. If evaluateConstantParameters() was called earlier, constant parameters will not be re-evaluated.

Parameters:

aggregate - evaluate aggregates

stop_at_null - stop if a null if found

Returns:

true if all parameters are non-null, false otherwise

Throws:

SQLException - if an error occurs

EndOfTable - if thrown by a parameter

evaluateParameters

protected boolean evaluateParameters(boolean aggregate)
                              throws SQLException,
                                     EndOfTable

Same as above version, but with stop_at_null set to false.

Parameters:

aggregate - evaluate aggregates

Returns:

true if all parameters are non-null, false otherwise

Throws:

SQLException - if an error occurs

EndOfTable - if thrown by a parameter

evaluate

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

Default implementation that simply calls evaluate(false).

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 a parameter

reset

public void reset()
           throws SQLException

This implementation simply calls reset() for all parameters and is intended to be used by non-aggregate functions. If any additional Function objects need to be reset, this method must be overridden.

Specified by:

reset in interface Function

Throws:

SQLException - if an error occurs

convertToSQLType

public static Object convertToSQLType(Object o,
                                      int type)
                               throws SQLException

Convert an Object to a compatible Object corresponding to the provided SQL type.

Parameters:

o - Object to convert

type - type from java.sql.Types to convert to

Returns:

Object of desired type (or null if o is null)

Throws:

SQLException - if no compatible type is available

getObjectSQLType

public static int getObjectSQLType(Object o)

Determine the SQL type of a java Object. If the reference is non-null, but the object type cannot be determined, java.sql.Types.JAVA_OBJECT is returned.

Parameters:

o - object to check

Returns:

value from java.sql.Types

getCompatableType

public static int getCompatableType(int t1,
                                    int t2)
                             throws SQLException

Determine a java.sql.Types type that is compatable with both of the passed parameters. If either parameter is NULL, the type of the other parameter will be returned.

Parameters:

t1 - type of first value

t2 - type of second value

Returns:

compatible type

Throws:

SQLException - if the types are incompatible