dialect.java

本文论述了一个前台笔记本销售系统的开发过程

package com.set.db.dialect;

/**
 * the strategis to deal with different db server for the purposes of being db
 * server independent
 * 
 * @author tommy.zeng
 * 
 */

public abstract class Dialect {
	protected Dialect() {
	}

	public boolean supportsLimitOffset() {
		return supportsLimit();
	}

	/**
	 * Add a LIMIT clause to the given SQL SELECT
	 */
	public String getLimitString(String querySelect, boolean hasOffset) {
		throw new UnsupportedOperationException("paged queries not supported");
	}

	public String getLimitString(String querySelect, boolean hasOffset,
			int limit) {
		return getLimitString(querySelect, hasOffset);
	}

	public boolean supportsVariableLimit() {
		return supportsLimit();
	}

	/**
	 * Does the LIMIT clause specify arguments in the "reverse" order limit,
	 * offset instead of offset, limit?
	 * 
	 * @return true if the correct order is limit, offset
	 */
	public boolean bindLimitParametersInReverseOrder() {
		return false;
	}

	/**
	 * Does the LIMIT clause come at the start of the SELECT statement, rather
	 * than at the end?
	 * 
	 * @return true if limit parameters should come before other parameters
	 */
	public boolean bindLimitParametersFirst() {
		return false;
	}

	/**
	 * Does the LIMIT clause take a "maximum" row number instead of a total
	 * number of returned rows?
	 */
	public boolean useMaxForLimit() {
		return false;
	}

	public boolean supportsLimit() {
		return false;
	}

	public String getQueryCountSql(final String sql) {
		int beginIdx = sql.toLowerCase().indexOf("select");
		int endIdx = sql.toLowerCase().indexOf("from");

		StringBuffer newSql = new StringBuffer(sql.length() + 10);
		if (beginIdx >= 0 && endIdx >= 0) {
			newSql.append("select count(*) as totalcnt ").append(
					sql.substring(endIdx));
		}

		// remove the order by clause
		int orderBy = newSql.toString().toLowerCase().indexOf("order by");
		if (orderBy > 0) {
			return newSql.substring(0, orderBy - 1);
		}

		return newSql.toString();

	}
}