Hibernate example source code file (DerbyConcatFunction.java)

This example Hibernate source code file (DerbyConcatFunction.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Hibernate tags/keywords

iterator, mapping, queryexception, queryexception, sessionfactoryimplementor, sqlfunction, string, string, stringbuffer, stringjointemplate, stringjointemplate, stringtransformer, stringtransformer, type, util

The Hibernate DerbyConcatFunction.java source code

/*
 * Hibernate, Relational Persistence for Idiomatic Java
 *
 * Copyright (c) 2010, Red Hat Inc. or third-party contributors as
 * indicated by the @author tags or express copyright attribution
 * statements applied by the authors.  All third-party contributions are
 * distributed under license by Red Hat Inc.
 *
 * This copyrighted material is made available to anyone wishing to use, modify,
 * copy, or redistribute it subject to the terms and conditions of the GNU
 * Lesser General Public License, as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Lesser General Public License
 * for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this distribution; if not, write to:
 * Free Software Foundation, Inc.
 * 51 Franklin Street, Fifth Floor
 * Boston, MA  02110-1301  USA
 */
package org.hibernate.dialect.function;
import java.util.Iterator;
import java.util.List;

import org.hibernate.QueryException;
import org.hibernate.engine.spi.Mapping;
import org.hibernate.engine.spi.SessionFactoryImplementor;
import org.hibernate.type.StandardBasicTypes;
import org.hibernate.type.Type;

/**
 * A specialized concat() function definition in which:<ol>
 * <li>we translate to use the concat operator ('||')
 * <li>wrap dynamic parameters in CASTs to VARCHAR
 * </ol>
 * <p/>
 * This last spec is to deal with a limitation on DB2 and variants (e.g. Derby)
 * where dynamic parameters cannot be used in concatenation unless they are being
 * concatenated with at least one non-dynamic operand.  And even then, the rules
 * are so convoluted as to what is allowed and when the CAST is needed and when
 * it is not that we just go ahead and do the CASTing.
 *
 * @author Steve Ebersole
 */
public class DerbyConcatFunction implements SQLFunction {
	/**
	 * {@inheritDoc}
	 * <p/>
	 * Here we always return <tt>true
	 */
	public boolean hasArguments() {
		return true;
	}

	/**
	 * {@inheritDoc}
	 * <p/>
	 * Here we always return <tt>true
	 */
	public boolean hasParenthesesIfNoArguments() {
		return true;
	}

	/**
	 * {@inheritDoc}
	 * <p/>
	 * Here we always return {@link StandardBasicTypes#STRING}.
	 */
	public Type getReturnType(Type argumentType, Mapping mapping) throws QueryException {
		return StandardBasicTypes.STRING;
	}

	/**
	 * {@inheritDoc}
	 * <p/>
	 * Here's the meat..  The whole reason we have a separate impl for this for Derby is to re-define
	 * this method.  The logic here says that if not all the incoming args are dynamic parameters
	 * (i.e. <tt>?) then we simply use the Derby concat operator (||) on the unchanged
	 * arg elements.  However, if all the args are dynamic parameters, then we need to wrap the individual
	 * arg elements in <tt>cast function calls, use the concatenation operator on the cast
	 * returns, and then wrap that whole thing in a call to the Derby <tt>varchar function.
	 */
	public String render(Type argumentType, List args, SessionFactoryImplementor factory) throws QueryException {
		boolean areAllArgsParams = true;
		Iterator itr = args.iterator();
		while ( itr.hasNext() ) {
			final String arg = ( String ) itr.next();
			if ( ! "?".equals( arg ) ) {
				areAllArgsParams = false;
				break;
			}
		}

		if ( areAllArgsParams ) {
			return join(
					args.iterator(),
					new StringTransformer() {
						public String transform(String string) {
							return "cast( ? as varchar(32672) )";
						}
					},
					new StringJoinTemplate() {
						public String getBeginning() {
							return "varchar( ";
						}
						public String getSeparator() {
							return " || ";
						}
						public String getEnding() {
							return " )";
						}
					}
			);
		}
		else {
			return join(
					args.iterator(),
					new StringTransformer() {
						public String transform(String string) {
							return string;
						}
					},
					new StringJoinTemplate() {
						public String getBeginning() {
							return "(";
						}
						public String getSeparator() {
							return "||";
						}
						public String getEnding() {
							return ")";
						}
					}
			);
		}
	}

	private static interface StringTransformer {
		public String transform(String string);
	}

	private static interface StringJoinTemplate {
		/**
		 * Getter for property 'beginning'.
		 *
		 * @return Value for property 'beginning'.
		 */
		public String getBeginning();
		/**
		 * Getter for property 'separator'.
		 *
		 * @return Value for property 'separator'.
		 */
		public String getSeparator();
		/**
		 * Getter for property 'ending'.
		 *
		 * @return Value for property 'ending'.
		 */
		public String getEnding();
	}

	private static String join(Iterator/*<String>*/ elements, StringTransformer elementTransformer, StringJoinTemplate template) {
		// todo : make this available via StringHelper?
		StringBuffer buffer = new StringBuffer( template.getBeginning() );
		while ( elements.hasNext() ) {
			final String element = ( String ) elements.next();
			buffer.append( elementTransformer.transform( element ) );
			if ( elements.hasNext() ) {
				buffer.append( template.getSeparator() );
			}
		}
		return buffer.append( template.getEnding() ).toString();
	}
}