using System;
using System.Collections.Generic;
using System.Data;
using System.Linq;
using System.Text;

namespace BLL
{
    public static class PagingHelper
    {
        /// <summary>
        /// 获取分页SQL语句，默认ROW_NUMBER为关健字，所有表不允许使用该字段名
        /// </summary>
        /// <param name="_recordCount">记录总数</param>
        /// <param name="_pageSize">每页记录数</param>
        /// <param name="_pageIndex">当前页数</param>
        /// <param name="_safeSql">SQL查询语句</param>
        /// <param name="_orderField">排序字段，多个则用“,”隔开</param>
        /// <returns>分页SQL语句</returns>
        public static DataTable CreatePage(int _pageSize, int _pageIndex, string _safeSql, string _orderField, IDataParameter[] parameters, out int RecordCount)
        {

            //拼接SQL字符串，加上ROW_NUMBER函数进行分页
            StringBuilder newSafeSql = new StringBuilder();
            newSafeSql.AppendFormat("SELECT ROW_NUMBER() OVER(ORDER BY {0}) as RowIndex,", _orderField);
            newSafeSql.Append(_safeSql.Substring(_safeSql.ToUpper().IndexOf("SELECT") + 6));

            //拼接成最终的SQL语句
            StringBuilder sbSql = new StringBuilder();
            sbSql.Append("SELECT * FROM (");
            sbSql.Append(newSafeSql.ToString());
            sbSql.Append(") AS T");
            sbSql.AppendFormat(" WHERE RowIndex > {0} and  RowIndex<={1}", ((_pageIndex - 1) * _pageSize), _pageIndex * _pageSize);
            sbSql.Append("  ");
            sbSql.AppendFormat(" SELECT COUNT(1) AS RecordCount FROM ({0}) AS T ", _safeSql);
            //return sbSql.ToString();
            DataSet ds = SQLHelper.RunSqlStrings(sbSql.ToString(), parameters);
            DataTable table = ds.Tables[0];
            RecordCount = int.Parse(ds.Tables[1].Rows[0]["RecordCount"].ToString());
            return table;

        }




    }
}