001    package org.apache.ojb.broker.accesslayer.sql;
002    
003    /* Copyright 2004-2005 The Apache Software Foundation
004     *
005     * Licensed under the Apache License, Version 2.0 (the "License");
006     * you may not use this file except in compliance with the License.
007     * You may obtain a copy of the License at
008     *
009     *     http://www.apache.org/licenses/LICENSE-2.0
010     *
011     * Unless required by applicable law or agreed to in writing, software
012     * distributed under the License is distributed on an "AS IS" BASIS,
013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014     * See the License for the specific language governing permissions and
015     * limitations under the License.
016     */
017    
018    import org.apache.ojb.broker.OJBRuntimeException;
019    import org.apache.ojb.broker.metadata.ClassDescriptor;
020    import org.apache.ojb.broker.metadata.FieldDescriptor;
021    import org.apache.ojb.broker.util.logging.Logger;
022    
023    /**
024     * Generate a select to check existence of an object.
025     * Something like "SELECT id_1 FROM myTable where id_1 = 123 and id_2 = 'kjngzt'".
026     *
027     * @author <a href="mailto:arminw@apache.org">Armin Waibel</a>
028     * @version $Id: SqlExistStatement.java,v 1.1 2007-08-24 22:17:39 ewestfal Exp $
029     */
030    public class SqlExistStatement extends SqlPkStatement
031    {
032        private static final String SELECT = "SELECT ";
033        private static final String FROM = " FROM ";
034    
035        private String sql;
036    
037        public SqlExistStatement(ClassDescriptor aCld, Logger aLogger)
038        {
039            super(aCld, aLogger);
040        }
041    
042        /** Return SELECT clause for object existence call */
043        public String getStatement()
044        {
045            if(sql == null)
046            {
047                StringBuffer stmt = new StringBuffer(128);
048                ClassDescriptor cld = getClassDescriptor();
049    
050                FieldDescriptor[] fieldDescriptors = cld.getPkFields();
051                if(fieldDescriptors == null || fieldDescriptors.length == 0)
052                {
053                    throw new OJBRuntimeException("No PK fields defined in metadata for " + cld.getClassNameOfObject());
054                }
055                FieldDescriptor field = fieldDescriptors[0];
056    
057                stmt.append(SELECT);
058                stmt.append(field.getColumnName());
059                stmt.append(FROM);
060                stmt.append(cld.getFullTableName());
061                appendWhereClause(cld, false, stmt);
062    
063                sql = stmt.toString();
064            }
065            return sql;
066        }
067    }