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SqlQueryPager.cs
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68 lines (57 loc) · 2.39 KB
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using System;
using System.Collections.Generic;
using System.ComponentModel.Composition;
using System.Linq;
using System.Text;
using System.Text.RegularExpressions;
using Simple.Data.Ado;
namespace Simple.Data.SqlServer
{
[Export(typeof(IQueryPager))]
public class SqlQueryPager : IQueryPager
{
private static readonly Regex ColumnExtract = new Regex(@"SELECT\s*(.*)\s*(FROM.*)", RegexOptions.Multiline | RegexOptions.IgnoreCase);
public IEnumerable<string> ApplyPaging(string sql, int skip, int take)
{
var builder = new StringBuilder("WITH __Data AS (SELECT ");
var match = ColumnExtract.Match(sql);
var columns = match.Groups[1].Value.Trim();
var fromEtc = match.Groups[2].Value.Trim();
builder.Append(columns);
var orderBy = ExtractOrderBy(columns, ref fromEtc);
builder.AppendFormat(", ROW_NUMBER() OVER({0}) AS [_#_]", orderBy);
builder.AppendLine();
builder.Append(fromEtc);
builder.AppendLine(")");
builder.AppendFormat("SELECT {0} FROM __Data WHERE [_#_] BETWEEN {1} AND {2}", DequalifyColumns(columns),
skip + 1, skip + take);
yield return builder.ToString();
}
private static string DequalifyColumns(string original)
{
var q = from part in original.Split(',')
select part.Substring(Math.Max(part.LastIndexOf('.') + 1, part.LastIndexOf('[')));
return string.Join(",", q);
}
private static string ExtractOrderBy(string columns, ref string fromEtc)
{
string orderBy;
int index = fromEtc.IndexOf("ORDER BY", StringComparison.InvariantCultureIgnoreCase);
if (index > -1)
{
orderBy = fromEtc.Substring(index).Trim();
fromEtc = fromEtc.Remove(index).Trim();
}
else
{
orderBy = "ORDER BY " + columns.Split(',').First().Trim();
var aliasIndex = orderBy.IndexOf(" AS [", StringComparison.InvariantCultureIgnoreCase);
if (aliasIndex > -1)
{
orderBy = orderBy.Substring(0, aliasIndex);
}
}
return orderBy;
}
}
}