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/*
 * Hibernate, Relational Persistence for Idiomatic Java
 *
 * License: GNU Lesser General Public License (LGPL), version 2.1 or later.
 * See the lgpl.txt file in the root directory or .
 */
package org.hibernate.dialect;

import java.sql.Types;

import org.hibernate.dialect.function.NoArgSQLFunction;
import org.hibernate.dialect.function.VarArgsSQLFunction;
import org.hibernate.dialect.identity.IdentityColumnSupport;
import org.hibernate.dialect.identity.Ingres9IdentityColumnSupport;
import org.hibernate.dialect.pagination.AbstractLimitHandler;
import org.hibernate.dialect.pagination.LimitHandler;
import org.hibernate.dialect.pagination.LimitHelper;
import org.hibernate.engine.spi.RowSelection;
import org.hibernate.type.StandardBasicTypes;

/**
 * A SQL dialect for Ingres 9.3 and later versions.
 * 
 * Changes:
 * 

 * Support for the SQL functions current_time, current_timestamp and current_date added
 * Type mapping of Types.TIMESTAMP changed from "timestamp with time zone" to "timestamp(9) with time zone"
 * Improved handling of "SELECT...FOR UPDATE" statements
 * Added support for pooled sequences
 * Added support for SELECT queries with limit and offset
 * Added getIdentitySelectString
 * Modified concatination operator
 * 
 *
 * @author Enrico Schenk
 * @author Raymond Fan
 */
public class Ingres9Dialect extends IngresDialect {

	private static final LimitHandler LIMIT_HANDLER = new AbstractLimitHandler() {
		@Override
		public String processSql(String sql, RowSelection selection) {
			final String soff = " offset " + selection.getFirstRow();
			final String slim = " fetch first " + getMaxOrLimit( selection ) + " rows only";
			final StringBuilder sb = new StringBuilder( sql.length() + soff.length() + slim.length() )
					.append( sql );
			if (LimitHelper.hasFirstRow( selection )) {
				sb.append( soff );
			}
			if (LimitHelper.hasMaxRows( selection )) {
				sb.append( slim );
			}
			return sb.toString();
		}

		@Override
		public boolean supportsLimit() {
			return true;
		}

		@Override
		public boolean supportsVariableLimit() {
			return false;
		}
	};

	/**
	 * Constructs a Ingres9Dialect
	 */
	public Ingres9Dialect() {
		super();
		registerDateTimeFunctions();
		registerDateTimeColumnTypes();
		registerFunction( "concat", new VarArgsSQLFunction( StandardBasicTypes.STRING, "(", "||", ")" ) );
	}

	/**
	 * Register functions current_time, current_timestamp, current_date
	 */
	protected void registerDateTimeFunctions() {
		registerFunction( "current_time", new NoArgSQLFunction( "current_time", StandardBasicTypes.TIME, false ) );
		registerFunction(
				"current_timestamp", new NoArgSQLFunction(
				"current_timestamp",
				StandardBasicTypes.TIMESTAMP,
				false
		)
		);
		registerFunction( "current_date", new NoArgSQLFunction( "current_date", StandardBasicTypes.DATE, false ) );
	}

	/**
	 * Register column types date, time, timestamp
	 */
	protected void registerDateTimeColumnTypes() {
		registerColumnType( Types.DATE, "ansidate" );
		registerColumnType( Types.TIMESTAMP, "timestamp(9) with time zone" );
	}

	// lock acquisition support ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

	@Override
	public boolean supportsOuterJoinForUpdate() {
		return false;
	}

	@Override
	public boolean forUpdateOfColumns() {
		return true;
	}

	// SEQUENCE support ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

	@Override
	public String getQuerySequencesString() {
		return "select seq_name from iisequences";
	}

	@Override
	public boolean supportsPooledSequences() {
		return true;
	}

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

	@Override
	public boolean isCurrentTimestampSelectStringCallable() {
		return false;
	}

	@Override
	public boolean supportsCurrentTimestampSelection() {
		return true;
	}

	@Override
	public String getCurrentTimestampSelectString() {
		return "select current_timestamp";
	}

	@Override
	public String getCurrentTimestampSQLFunctionName() {
		return "current_timestamp";
	}

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

	@Override
	public boolean supportsUnionAll() {
		return true;
	}

	// Informational metadata ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

	@Override
	public boolean doesReadCommittedCauseWritersToBlockReaders() {
		return true;
	}

	@Override
	public boolean doesRepeatableReadCauseReadersToBlockWriters() {
		return true;
	}

	// limit/offset support ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

	@Override
	public LimitHandler getDefaultLimitHandler() {
		return LIMIT_HANDLER;
	}

	@Override
	public boolean supportsLimitOffset() {
		return true;
	}

	@Override
	public boolean supportsVariableLimit() {
		return false;
	}

	@Override
	public boolean useMaxForLimit() {
		return false;
	}

	@Override
	public String getLimitString(String querySelect, int offset, int limit) {
		final StringBuilder soff = new StringBuilder( " offset " + offset );
		final StringBuilder slim = new StringBuilder( " fetch first " + limit + " rows only" );
		final StringBuilder sb = new StringBuilder( querySelect.length() + soff.length() + slim.length() )
				.append( querySelect );
		if ( offset > 0 ) {
			sb.append( soff );
		}
		if ( limit > 0 ) {
			sb.append( slim );
		}
		return sb.toString();
	}

	@Override
	public IdentityColumnSupport getIdentityColumnSupport() {
		return new Ingres9IdentityColumnSupport();
	}
}