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Hibernate's core ORM functionality

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/*
 * Hibernate, Relational Persistence for Idiomatic Java
 *
 * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
 * See the lgpl.txt file in the root directory or .
 */
package org.hibernate.dialect.function;

import java.util.Arrays;
import java.util.HashSet;
import java.util.List;
import java.util.Set;

import org.hibernate.type.StandardBasicTypes;

/**
 * When "substring" function is used for DB2, this implementation of {@link StandardSQLFunction}
 * will render "substr" or "substring", depending on the last argument being used. If the last
 * argument is a string unit ("CODEUNITS16", "CODEUNITS32", or "OCTETS"), then the function
 * will be rendered as "substring"; otherwise, it will be rendered as "substr".
 * 
 * ANSI SQL-92 standard defines "substring" without string units, which is more similar to DB2's "substr",
 * so it makes sense to use DB2's "substr" function when string units are not provided.
 * 
 * Background: DB2 has both "substr" and "substring", which are different functions that are not
 * interchangeable. Prior to DB2 11.1, DB2's "substring" function requires an argument for string
 * units; without this argument, DB2 throws an exception. DB2's "substr" function throws an exception
 * if string unit is provided as an argument.
 *
 * @author Gail Badner
 */
public class DB2SubstringFunction extends StandardSQLFunction {
	private static final Set possibleStringUnits = new HashSet<>(
			Arrays.asList( "CODEUNITS16", "CODEUNITS32", "OCTETS" )
	);

	public DB2SubstringFunction() {
		super( "substring", StandardBasicTypes.STRING  );
	}

	@Override
	protected String getRenderedName(List arguments) {
		final String lastArgument = (String) arguments.get( arguments.size() - 1 );
		if ( lastArgument != null && possibleStringUnits.contains( lastArgument.toUpperCase() ) ) {
			return getName();
		}
		else{
			return "substr";
		}
	}
}