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  package org.apache.cayenne.dba.mysql;
  
  import java.sql.Connection;
  import java.sql.ResultSet;
  import java.sql.SQLException;
  import java.sql.Statement;
  import java.util.Collections;
  
  import org.apache.cayenne.access.DataNode;
  import org.apache.cayenne.dba.JdbcAdapter;
  import org.apache.cayenne.dba.JdbcPkGenerator;
  import org.apache.cayenne.map.DbEntity;
  import org.apache.cayenne.tx.BaseTransaction;
  import org.apache.cayenne.tx.Transaction;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /**
   */
  public class MySQLPkGenerator extends JdbcPkGenerator {
  
      private static final Logger logger = LoggerFactory.getLogger(MySQLPkGenerator.class);
  
      /**
       * Used by DI
       * @since 4.1
       */
      public MySQLPkGenerator() {
          super();
      }
  
      MySQLPkGenerator(JdbcAdapter adapter) {
          super(adapter);
      }
  
      /**
       * Overrides superclass's implementation to perform locking of the primary
       * key lookup table.
       *
       * @since 3.0
       */
      @Override
      protected long longPkFromDatabase(DataNode node, DbEntity entity) throws Exception {
  
          // must work directly with JDBC connection, since we
          // must unlock the AUTO_PK_SUPPORT table in case of
          // failures.... ah..JDBC is fun...
  
          // chained SQL exception
          SQLException exception = null;
          long pk = -1L;
  
          // Start new transaction if needed, can any way lead to problems when
          // using external transaction manager. We can only warn about it.
          // See https://issues.apache.org/jira/browse/CAY-2186 for details.
          Transaction transaction = BaseTransaction.getThreadTransaction();
          if (transaction != null && transaction.isExternal()) {
              logger.warn("Using MysqlPkGenerator with external transaction manager may lead to inconsistent state.");
          }
          BaseTransaction.bindThreadTransaction(null);
  
          try (Connection con = node.getDataSource().getConnection()) {
  
              if (con.getAutoCommit()) {
                  con.setAutoCommit(false);
              }
  
              try (Statement st = con.createStatement()) {
                  try {
                      pk = getLongPrimaryKey(st, entity.getName());
                      con.commit();
                  } catch (SQLException pkEx) {
                      try {
                          con.rollback();
                      } catch (SQLException ignored) {
                      }
  
                      exception = processSQLException(pkEx, null);
                  } finally {
                      // UNLOCK!
                      // THIS MUST BE EXECUTED NO MATTER WHAT, OR WE WILL LOCK THE PRIMARY KEY TABLE!!
                      try {
                          String unlockString = "UNLOCK TABLES";
                          adapter.getJdbcEventLogger().log(unlockString);
                          st.execute(unlockString);
                      } catch (SQLException unlockEx) {
                          exception = processSQLException(unlockEx, exception);
                      }
                  }
              }
          } catch (SQLException otherEx) {
              exception = processSQLException(otherEx, null);
          } finally {
              BaseTransaction.bindThreadTransaction(transaction);
          }
  
          // check errors
          if (exception != null) {
              throw exception;
          }
  
          return pk;
  
      }
  
      /**
       * Appends a new SQLException to the chain. If parent is null, uses the
       * exception as the chain root.
       */
      protected SQLException processSQLException(SQLException exception, SQLException parent) {
          if (parent == null) {
              return exception;
          }
  
          parent.setNextException(exception);
          return parent;
      }
  
      @Override
      protected String dropAutoPkString() {
          return "DROP TABLE IF EXISTS AUTO_PK_SUPPORT";
      }
  
      @Override
      protected String pkTableCreateString() {
          return "CREATE TABLE IF NOT EXISTS AUTO_PK_SUPPORT " +
                  "(TABLE_NAME CHAR(100) NOT NULL, NEXT_ID BIGINT NOT NULL, UNIQUE (TABLE_NAME)) " +
                  "ENGINE=" + MySQLAdapter.DEFAULT_STORAGE_ENGINE;
      }
  
      /**
       * @since 3.0
       */
      protected long getLongPrimaryKey(Statement statement, String entityName) throws SQLException {
          // lock
          String lockString = "LOCK TABLES AUTO_PK_SUPPORT WRITE";
          adapter.getJdbcEventLogger().log(lockString);
          statement.execute(lockString);
  
          // select
          String selectString = super.pkSelectString(entityName);
          adapter.getJdbcEventLogger().log(selectString);
          long pk;
          try (ResultSet rs = statement.executeQuery(selectString)) {
              if (!rs.next()) {
                  throw new SQLException("No rows for '" + entityName + "'");
              }
  
              pk = rs.getLong(1);
              if (rs.next()) {
                  throw new SQLException("More than one row for '" + entityName + "'");
              }
          }
  
          // update
          String updateString = super.pkUpdateString(entityName) + " AND NEXT_ID = " + pk;
          adapter.getJdbcEventLogger().log(updateString);
          int updated = statement.executeUpdate(updateString);
          // optimistic lock failure...
          if (updated != 1) {
              throw new SQLException("Error updating PK count '" + entityName + "': " + updated);
          }
  
          return pk;
      }
  }
  