/**

 * 用于辅助拼接HQL语句

 */

public class QueryHelper {

    private String fromClause; // FROM子句

    private String whereClause = ""; // Where子句

    private String orderByClause = ""; // OrderBy子句

    private List<Object> parameters = new ArrayList<Object>(); // 参数列表

    /**

     * 生成From子句

     * @param clazz

     * @param alias

     *            别名

     */

    public QueryHelper(Class clazz, String alias) {

        fromClause = "FROM " + clazz.getSimpleName() + " " + alias;

    }

    /**

     * 拼接Where子句

     * @param condition

     * @param params

     */

    public QueryHelper addCondition(String condition, Object... params) {

        // 拼接

        if (whereClause.length() == 0) {

            whereClause = " WHERE " + condition;

        } else {

            whereClause += " AND " + condition;

        }

        // 参数

        if (params != null) {

            for (Object p : params) {

                parameters.add(p);

            }

        }

        return this;

    }

    /**

     * 如果第一个参数为true，则拼接Where子句

     * @param append

     * @param condition

     * @param params

     */

    public QueryHelper addCondition(boolean append, String condition,

            Object... params) {

        if (append) {

            addCondition(condition, params);

        }

        return this;

    }

    /**

     * 拼接OrderBy子句

     * @param propertyName

     *            参与排序的属性名

     * @param asc

     *            true表示升序，false表示降序

     */

    public QueryHelper addOrderProperty(String propertyName, boolean asc) {

        if (orderByClause.length() == 0) {

            orderByClause = " ORDER BY " + propertyName

                    + (asc ? " ASC" : " DESC");

        } else {

            orderByClause += ", " + propertyName + (asc ? " ASC" : " DESC");

        }

        return this;

    }

    /**

     * 如果第一个参数为true，则拼接OrderBy子句

     * @param append

     * @param propertyName

     * @param asc

     */

    public QueryHelper addOrderProperty(boolean append, String propertyName,

            boolean asc) {

        if (append) {

            addOrderProperty(propertyName, asc);

        }

        return this;

    }

    /**

     * 获取生成的用于查询数据列表的HQL语句

     * @return

     */

    public String getListQueryHql() {

        return fromClause + whereClause + orderByClause;

    }

    /**

     * 获取生成的用于查询总记录数的HQL语句

     * @return

     */

    public String getCountQueryHql() {

        return "SELECT COUNT(*) " + fromClause + whereClause;

    }

    /**

     * 获取HQL中的参数值列表

     * @return

     */

    public List<Object> getParameters() {

        return parameters;

    }

}