dialect.java

hibernate-distribution-3.3.1.GA-dist.zip源码

		else {
			return "";
		}
	}

	/**
	 * Get the string to append to SELECT statements to acquire locks
	 * for this dialect.
	 *
	 * @return The appropriate <tt>FOR UPDATE</tt> clause string.
	 */
	public String getForUpdateString() {
		return " for update";
	}

	/**
	 * Is <tt>FOR UPDATE OF</tt> syntax supported?
	 *
	 * @return True if the database supports <tt>FOR UPDATE OF</tt> syntax;
	 * false otherwise.
	 */
	public boolean forUpdateOfColumns() {
		// by default we report no support
		return false;
	}

	/**
	 * Does this dialect support <tt>FOR UPDATE</tt> in conjunction with
	 * outer joined rows?
	 *
	 * @return True if outer joined rows can be locked via <tt>FOR UPDATE</tt>.
	 */
	public boolean supportsOuterJoinForUpdate() {
		return true;
	}

	/**
	 * Get the <tt>FOR UPDATE OF column_list</tt> fragment appropriate for this
	 * dialect given the aliases of the columns to be write locked.
	 *
	 * @param aliases The columns to be write locked.
	 * @return The appropriate <tt>FOR UPDATE OF column_list</tt> clause string.
	 */
	public String getForUpdateString(String aliases) {
		// by default we simply return the getForUpdateString() result since
		// the default is to say no support for "FOR UPDATE OF ..."
		return getForUpdateString();
	}

	/**
	 * Retrieves the <tt>FOR UPDATE NOWAIT</tt> syntax specific to this dialect.
	 *
	 * @return The appropriate <tt>FOR UPDATE NOWAIT</tt> clause string.
	 */
	public String getForUpdateNowaitString() {
		// by default we report no support for NOWAIT lock semantics
		return getForUpdateString();
	}

	/**
	 * Get the <tt>FOR UPDATE OF column_list NOWAIT</tt> fragment appropriate
	 * for this dialect given the aliases of the columns to be write locked.
	 *
	 * @param aliases The columns to be write locked.
	 * @return The appropriate <tt>FOR UPDATE colunm_list NOWAIT</tt> clause string.
	 */
	public String getForUpdateNowaitString(String aliases) {
		return getForUpdateString( aliases );
	}

	/**
	 * Some dialects support an alternative means to <tt>SELECT FOR UPDATE</tt>,
	 * whereby a "lock hint" is appends to the table name in the from clause.
	 * <p/>
	 * contributed by <a href="http://sourceforge.net/users/heschulz">Helge Schulz</a>
	 *
	 * @param mode The lock mode to apply
	 * @param tableName The name of the table to which to apply the lock hint.
	 * @return The table with any required lock hints.
	 */
	public String appendLockHint(LockMode mode, String tableName) {
		return tableName;
	}

	/**
	 * Modifies the given SQL by applying the appropriate updates for the specified
	 * lock modes and key columns.
	 * <p/>
	 * The behavior here is that of an ANSI SQL <tt>SELECT FOR UPDATE</tt>.  This
	 * method is really intended to allow dialects which do not support
	 * <tt>SELECT FOR UPDATE</tt> to achieve this in their own fashion.
	 *
	 * @param sql the SQL string to modify
	 * @param aliasedLockModes a map of lock modes indexed by aliased table names.
	 * @param keyColumnNames a map of key columns indexed by aliased table names.
	 * @return the modified SQL string.
	 */
	public String applyLocksToSql(String sql, Map aliasedLockModes, Map keyColumnNames) {
		return sql + new ForUpdateFragment( this, aliasedLockModes, keyColumnNames ).toFragmentString();
	}


	// table support ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

	/**
	 * Command used to create a table.
	 *
	 * @return The command used to create a table.
	 */
	public String getCreateTableString() {
		return "create table";
	}

	/**
	 * Slight variation on {@link #getCreateTableString}.  Here, we have the
	 * command used to create a table when there is no primary key and
	 * duplicate rows are expected.
	 * <p/>
	 * Most databases do not care about the distinction; originally added for
	 * Teradata support which does care.
	 *
	 * @return The command used to create a multiset table.
	 */
	public String getCreateMultisetTableString() {
		return getCreateTableString();
	}


	// temporary table support ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

	/**
	 * Does this dialect support temporary tables?
	 *
	 * @return True if temp tables are supported; false otherwise.
	 */
	public boolean supportsTemporaryTables() {
		return false;
	}

	/**
	 * Generate a temporary table name given the bas table.
	 *
	 * @param baseTableName The table name from which to base the temp table name.
	 * @return The generated temp table name.
	 */
	public String generateTemporaryTableName(String baseTableName) {
		return "HT_" + baseTableName;
	}

	/**
	 * Command used to create a temporary table.
	 *
	 * @return The command used to create a temporary table.
	 */
	public String getCreateTemporaryTableString() {
		return "create table";
	}

	/**
	 * Get any fragments needing to be postfixed to the command for
	 * temporary table creation.
	 *
	 * @return Any required postfix.
	 */
	public String getCreateTemporaryTablePostfix() {
		return "";
	}

	/**
	 * Does the dialect require that temporary table DDL statements occur in
	 * isolation from other statements?  This would be the case if the creation
	 * would cause any current transaction to get committed implicitly.
	 * <p/>
	 * JDBC defines a standard way to query for this information via the
	 * {@link java.sql.DatabaseMetaData#dataDefinitionCausesTransactionCommit()}
	 * method.  However, that does not distinguish between temporary table
	 * DDL and other forms of DDL; MySQL, for example, reports DDL causing a
	 * transaction commit via its driver, even though that is not the case for
	 * temporary table DDL.
	 * <p/>
	 * Possible return values and their meanings:<ul>
	 * <li>{@link Boolean#TRUE} - Unequivocally, perform the temporary table DDL
	 * in isolation.</li>
	 * <li>{@link Boolean#FALSE} - Unequivocally, do <b>not</b> perform the
	 * temporary table DDL in isolation.</li>
	 * <li><i>null</i> - defer to the JDBC driver response in regards to
	 * {@link java.sql.DatabaseMetaData#dataDefinitionCausesTransactionCommit()}</li>
	 * </ul>
	 * 
	 * @return see the result matrix above.
	 */
	public Boolean performTemporaryTableDDLInIsolation() {
		return null;
	}

	/**
	 * Do we need to drop the temporary table after use?
	 *
	 * @return True if the table should be dropped.
	 */
	public boolean dropTemporaryTableAfterUse() {
		return true;
	}


	// callable statement support ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

	/**
	 * Registers an OUT parameter which will be returing a
	 * {@link java.sql.ResultSet}.  How this is accomplished varies greatly
	 * from DB to DB, hence its inclusion (along with {@link #getResultSet}) here.
	 *
	 * @param statement The callable statement.
	 * @param position The bind position at which to register the OUT param.
	 * @return The number of (contiguous) bind positions used.
	 * @throws SQLException Indicates problems registering the OUT param.
	 */
	public int registerResultSetOutParameter(CallableStatement statement, int position) throws SQLException {
		throw new UnsupportedOperationException(
				getClass().getName() +
				" does not support resultsets via stored procedures"
			);
	}

	/**
	 * Given a callable statement previously processed by {@link #registerResultSetOutParameter},
	 * extract the {@link java.sql.ResultSet} from the OUT parameter.
	 *
	 * @param statement The callable statement.
	 * @return The extracted result set.
	 * @throws SQLException Indicates problems extracting the result set.
	 */
	public ResultSet getResultSet(CallableStatement statement) throws SQLException {
		throw new UnsupportedOperationException(
				getClass().getName() +
				" does not support resultsets via stored procedures"
			);
	}

	// current timestamp support ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

	/**
	 * Does this dialect support a way to retrieve the database's current
	 * timestamp value?
	 *
	 * @return True if the current timestamp can be retrieved; false otherwise.
	 */
	public boolean supportsCurrentTimestampSelection() {
		return false;
	}

	/**
	 * Should the value returned by {@link #getCurrentTimestampSelectString}
	 * be treated as callable.  Typically this indicates that JDBC escape
	 * sytnax is being used...
	 *
	 * @return True if the {@link #getCurrentTimestampSelectString} return
	 * is callable; false otherwise.
	 */
	public boolean isCurrentTimestampSelectStringCallable() {
		throw new UnsupportedOperationException( "Database not known to define a current timestamp function" );
	}

	/**
	 * Retrieve the command used to retrieve the current timestammp from the
	 * database.
	 *
	 * @return The command.
	 */
	public String getCurrentTimestampSelectString() {
		throw new UnsupportedOperationException( "Database not known to define a current timestamp function" );
	}

	/**
	 * The name of the database-specific SQL function for retrieving the
	 * current timestamp.
	 *
	 * @return The function name.
	 */
	public String getCurrentTimestampSQLFunctionName() {
		// the standard SQL function name is current_timestamp...
		return "current_timestamp";
	}


	// SQLException support ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

	/**
	 * Build an instance of the SQLExceptionConverter preferred by this dialect for
	 * converting SQLExceptions into Hibernate's JDBCException hierarchy.  The default
	 * Dialect implementation simply returns a converter based on X/Open SQLState codes.
	 * <p/>
	 * It is strongly recommended that specific Dialect implementations override this
	 * method, since interpretation of a SQL error is much more accurate when based on
	 * the ErrorCode rather than the SQLState.  Unfortunately, the ErrorCode is a vendor-
	 * specific approach.
	 *
	 * @return The Dialect's preferred SQLExceptionConverter.
	 */
	public SQLExceptionConverter buildSQLExceptionConverter() {
		// The default SQLExceptionConverter for all dialects is based on SQLState
		// since SQLErrorCode is extremely vendor-specific.  Specific Dialects
		// may override to return whatever is most appropriate for that vendor.
		return new SQLStateConverter( getViolatedConstraintNameExtracter() );
	}

	private static final ViolatedConstraintNameExtracter EXTRACTER = new ViolatedConstraintNameExtracter() {
		public String extractConstraintName(SQLException sqle) {
			return null;
		}
	};

	public ViolatedConstraintNameExtracter getViolatedConstraintNameExtracter() {
		return EXTRACTER;
	}


	// union subclass support ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

	/**
	 * Given a {@link java.sql.Types} type code, determine an appropriate
	 * null value to use in a select clause.
	 * <p/>
	 * One thing to consider here is that certain databases might
	 * require proper casting for the nulls here since the select here
	 * will be part of a UNION/UNION ALL.
	 *
	 * @param sqlType The {@link java.sql.Types} type code.
	 * @return The appropriate select clause value fragment.
	 */
	public String getSelectClauseNullString(int sqlType) {
		return "null";
	}

	/**
	 * Does this dialect support UNION ALL, which is generally a faster
	 * variant of UNION?
	 *
	 * @return True if UNION ALL is supported; false otherwise.
	 */
	public boolean supportsUnionAll() {
		return false;
	}


	// miscellaneous support ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~


	/**
	 * Create a {@link org.hibernate.sql.JoinFragment} strategy responsible
	 * for handling this dialect's variations in how joins are handled.
	 *
	 * @return This dialect's {@link org.hibernate.sql.JoinFragment} strategy.
	 */
	public JoinFragment createOuterJoinFragment() {
		return new ANSIJoinFragment();
	}

	/**
	 * Create a {@link org.hibernate.sql.CaseFragment} strategy responsible
	 * for handling this dialect's variations in how CASE statements are
	 * handled.
	 *
	 * @return This dialect's {@link org.hibernate.sql.CaseFragment} strategy.
	 */
	public CaseFragment createCaseFragment() {
		return new ANSICaseFragment();
	}

	/**
	 * The fragment used to insert a row without specifying any column values.
	 * This is not possible on some databases.
	 *
	 * @return The appropriate empty values clause.
	 */
	public String getNoColumnsInsertString() {
		return "values ( )";
	}

	/**
	 * The name of the SQL function that transforms a string to
	 * lowercase
	 *
	 * @return The dialect-specific lowercase function.
	 */
	public String getLowercaseFunction() {
		return "lower";
	}

	/**
	 * Meant as a means for end users to affect the select strings being sent
	 * to the database and perhaps manipulate them in some fashion.
	 * <p/>
	 * The recommend approach is to instead use
	 * {@link org.hibernate.Interceptor#onPrepareStatement(String)}.
	 *
	 * @param select The select command
	 * @return The mutated select command, or the same as was passed in.
	 */
	public String transformSelectString(String select) {
		return select;
	}

	/**
	 * What is the maximum length Hibernate can use for generated aliases?
	 *
	 * @return The maximum length.
	 */
	public int getMaxAliasLength() {
		return 10;
	}

	/**
	 * The SQL literal value to which this database maps boolean values.
	 *
	 * @param bool The boolean value
	 * @return The appropriate SQL literal.
	 */
	public String toBooleanValueString(boolean bool) {
		return bool ? "1" : "0";
	}


	// identifier quoting support ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

	/**
	 * The character specific to this dialect used to begin a quoted identifier.
	 *
	 * @return The dialect's specific open quote character.
	 */
	public char openQuote() {
		return '"';
	}

	/**
	 * The character specific to this dialect used to close a quoted identifier.
	 *
	 * @return The dialect's specific close quote character.
	 */
	public char closeQuote() {
		return '"';
	}

	/**
	 * Apply dialect-specific quoting.
	 * <p/>
	 * By default, the incoming value is checked to see if its first character