001package com.randomnoun.common.jexl.sql;
002
003import java.util.*;
004
005import com.randomnoun.common.jexl.eval.*;
006
007/**
008 * A function which can be translated into SQL. These functions should be
009 * set in an SqlGenerator's context to allow expressions to use those functions.
010 *
011 * <p>This class defines a number of 'standard' functions, which can be used;
012 * they subclass the functions in EvalFunction of the same name, so that they can work
013 * in both the Evaluator and SqlGenerator AST visitors.
014 *
015 * 
016 * @author knoxg
017 */
018public interface SqlFunction {
019
020        /** All SQL functions must implement this method. It returns the SQL required for
021         *  the database to evaluate the function. evalContext can be used to get the
022         *  database type, if required.
023         *
024         * @param functionName The name of the function being translated
025         * @param evalContext  The evaluation context of the SqlGenerator doing the translation
026         * @param arguments    The arguments to the function
027         *
028         * @return the SQL representation of the function
029         * @throws EvalException If an exception occured during translation (e.g. missing arguments, arguments of wrong type, invalid arguments).
030         * @throws EvalFallbackException If this expression should be evaluated at runtime instead of being translated  
031         */
032        public abstract String toSql(String functionName, EvalContext evalContext, List<Object> arguments)
033                throws EvalException, EvalFallbackException;
034}