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 *  regarding copyright ownership.  The ASF licenses this file
 *  to you under the Apache License, Version 2.0 (the
 *  "License"); you may not use this file except in compliance
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 *  Unless required by applicable law or agreed to in writing,
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package org.apache.cayenne.dba.oracle;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Iterator;
import java.util.List;

import org.apache.cayenne.CayenneRuntimeException;
import org.apache.cayenne.access.DataNode;
import org.apache.cayenne.access.QueryLogger;
import org.apache.cayenne.dba.JdbcPkGenerator;
import org.apache.cayenne.map.DbEntity;
import org.apache.cayenne.map.DbKeyGenerator;

/**
 * Sequence-based primary key generator implementation for Oracle. Uses Oracle sequences
 * to generate primary key values. This approach is at least 50% faster when tested with
 * Oracle compared to the lookup table approach.
 * <p>
 * When using Cayenne key caching mechanism, make sure that sequences in the database have
 * "INCREMENT BY" greater or equal to OraclePkGenerator "pkCacheSize" property value. If
 * this is not the case, you will need to adjust PkGenerator value accordingly. For
 * example when sequence is incremented by 1 each time, use the following code:
 * </p>
 * 
 * <pre>
 * dataNode.getAdapter().getPkGenerator().setPkCacheSize(1);
 * </pre>
 * 
 * @author Andrus Adamchik
 */
public class OraclePkGenerator extends JdbcPkGenerator {

    private static final String _SEQUENCE_PREFIX = "pk_";

    public void createAutoPk(DataNode node, List dbEntities) throws Exception {
        List sequences = getExistingSequences(node);

        // create needed sequences
        Iterator it = dbEntities.iterator();
        while (it.hasNext()) {
            DbEntity ent = (DbEntity) it.next();
            if (!sequences.contains(sequenceName(ent))) {
                runUpdate(node, createSequenceString(ent));
            }
        }
    }

    public List createAutoPkStatements(List dbEntities) {
        List list = new ArrayList();
        Iterator it = dbEntities.iterator();
        while (it.hasNext()) {
            DbEntity ent = (DbEntity) it.next();
            list.add(createSequenceString(ent));
        }

        return list;
    }

    public void dropAutoPk(DataNode node, List dbEntities) throws Exception {
        List sequences = getExistingSequences(node);

        // drop obsolete sequences
        Iterator it = dbEntities.iterator();
        while (it.hasNext()) {
            DbEntity ent = (DbEntity) it.next();
            if (sequences.contains(stripSchemaName(sequenceName(ent)))) {
                runUpdate(node, dropSequenceString(ent));
            }
        }
    }

    public List dropAutoPkStatements(List dbEntities) {
        List list = new ArrayList();
        Iterator it = dbEntities.iterator();
        while (it.hasNext()) {
            DbEntity ent = (DbEntity) it.next();
            list.add(dropSequenceString(ent));
        }

        return list;
    }

    protected String createSequenceString(DbEntity ent) {
        StringBuffer buf = new StringBuffer();
        buf
                .append("CREATE SEQUENCE ")
                .append(sequenceName(ent))
                .append(" START WITH 200")
                .append(" INCREMENT BY ")
                .append(pkCacheSize(ent));
        return buf.toString();
    }

    /**
     * Returns a SQL string needed to drop any database objects associated with automatic
     * primary key generation process for a specific DbEntity.
     */
    protected String dropSequenceString(DbEntity ent) {
        StringBuffer buf = new StringBuffer();
        buf.append("DROP SEQUENCE ").append(sequenceName(ent));
        return buf.toString();
    }

    /**
     * Generates primary key by calling Oracle sequence corresponding to the
     * <code>dbEntity</code>. Executed SQL looks like this:
     * 
     * <pre>
     *   SELECT pk_table_name.nextval FROM DUAL
     * </pre>
     */
    protected int pkFromDatabase(DataNode node, DbEntity ent) throws Exception {

        DbKeyGenerator pkGenerator = ent.getPrimaryKeyGenerator();
        String pkGeneratingSequenceName;
        if (pkGenerator != null
                && DbKeyGenerator.ORACLE_TYPE.equals(pkGenerator.getGeneratorType())
                && pkGenerator.getGeneratorName() != null)
            pkGeneratingSequenceName = pkGenerator.getGeneratorName();
        else
            pkGeneratingSequenceName = sequenceName(ent);

        Connection con = node.getDataSource().getConnection();
        try {
            Statement st = con.createStatement();
            try {
                String sql = "SELECT " + pkGeneratingSequenceName + ".nextval FROM DUAL";
                QueryLogger.logQuery(sql, Collections.EMPTY_LIST);
                ResultSet rs = st.executeQuery(sql);
                try {
                    // Object pk = null;
                    if (!rs.next()) {
                        throw new CayenneRuntimeException(
                                "Error generating pk for DbEntity " + ent.getName());
                    }
                    return rs.getInt(1);
                }
                finally {
                    rs.close();
                }
            }
            finally {
                st.close();
            }
        }
        finally {
            con.close();
        }
    }

    protected int pkCacheSize(DbEntity entity) {
        // use custom generator if possible
        DbKeyGenerator keyGenerator = entity.getPrimaryKeyGenerator();
        if (keyGenerator != null
                && DbKeyGenerator.ORACLE_TYPE.equals(keyGenerator.getGeneratorType())
                && keyGenerator.getGeneratorName() != null) {

            Integer size = keyGenerator.getKeyCacheSize();
            return (size != null && size.intValue() >= 1) ? size.intValue() : super
                    .getPkCacheSize();
        }
        else {
            return super.getPkCacheSize();
        }
    }

    /** Returns expected primary key sequence name for a DbEntity. */
    protected String sequenceName(DbEntity entity) {

        // use custom generator if possible
        DbKeyGenerator keyGenerator = entity.getPrimaryKeyGenerator();
        if (keyGenerator != null
                && DbKeyGenerator.ORACLE_TYPE.equals(keyGenerator.getGeneratorType())
                && keyGenerator.getGeneratorName() != null) {

            return keyGenerator.getGeneratorName().toLowerCase();
        }
        else {
            String entName = entity.getName();
            String seqName = _SEQUENCE_PREFIX + entName.toLowerCase();

            if (entity.getSchema() != null && entity.getSchema().length() > 0) {
                seqName = entity.getSchema() + "." + seqName;
            }
            return seqName;
        }
    }

    protected String stripSchemaName(String sequenceName) {
        int ind = sequenceName.indexOf('.');
        return (ind >= 0) ? sequenceName.substring(ind + 1) : sequenceName;
    }

    /**
     * Fetches a list of existing sequences that might match Cayenne generated ones.
     */
    protected List getExistingSequences(DataNode node) throws SQLException {

        // check existing sequences
        Connection con = node.getDataSource().getConnection();

        try {
            Statement sel = con.createStatement();
            try {
                String sql = "SELECT LOWER(SEQUENCE_NAME) FROM ALL_SEQUENCES";
                QueryLogger.logQuery(sql, Collections.EMPTY_LIST);
                ResultSet rs = sel.executeQuery(sql);
                try {
                    List sequenceList = new ArrayList();
                    while (rs.next()) {
                        sequenceList.add(rs.getString(1));
                    }
                    return sequenceList;
                }
                finally {
                    rs.close();
                }
            }
            finally {
                sel.close();
            }
        }
        finally {
            con.close();
        }
    }
}
