How to simulate regular expressions in LINQ-to-SQL

Question

I have a database table with customer account numbers. Within the same table are test accounts that don\'t match the production formatting: say, \'A1111\' is production but

Answer 1

special thanks to Roman Khramtsov and db_developer for reference information, and thanks to Microsoft :P

RegExpLike Extension For Sql Server

Reference links:
http://www.codeproject.com/Articles/42764/Regular-Expressions-in-MS-SQL-Server-2005-2008
http://msdn.microsoft.com/en-us/library/dd456847.aspx

Step1: Compile SqlRegularExpressions.cs to generate SqlRegularExpressions.dll

// SqlRegularExpressions.cs
// © Copyright 2009, Roman Khramtsov / Major League - SqlRegularExpressions

using System;
using System.Data.SqlTypes;         //SqlChars
using System.Collections;           //IEnumerable
using System.Text.RegularExpressions;   //Match, Regex
using Microsoft.SqlServer.Server;       //SqlFunctionAttribute

/// 

/// Class that allows to support regular expressions in MS SQL Server 2005/2008
/// 
public partial class SqlRegularExpressions
{
    /// 

    /// Checks string on match to regular expression
    /// 
    /// string to check
    /// regular expression
    /// true - text consists match one at least, false - no matches
    [SqlFunction]
    public static bool Like(string text, string pattern, int options)
    {
        return (Regex.IsMatch(text, pattern, (RegexOptions)options));
    }

    /// 

    /// Gets matches from text using pattern
    /// 
    /// text to parse
    /// regular expression pattern
    /// MatchCollection
    [SqlFunction(FillRowMethodName = "FillMatch")]
    public static IEnumerable GetMatches(string text, string pattern, int options)
    {
        return Regex.Matches(text, pattern, (RegexOptions)options);
    }

    /// 

    /// Parses match-object and returns its parameters 
    /// 
    /// Match-object
    /// TThe zero-based starting position in the original string where the captured
    ///     substring was found
    /// The length of the captured substring.
    /// The actual substring that was captured by the match.
    public static void FillMatch(object obj, out int index, out int length, out SqlChars value)
    {
        Match match = (Match)obj;
        index = match.Index;
        length = match.Length;
        value = new SqlChars(match.Value);
    }

}

Step 2: Run DbInstall.sql SQL on the database

DbInstall.sql

sp_configure 'clr enabled', 1
reconfigure
go

--needs full path to DLL
create assembly SqlRegularExpressions 
from '..\SqlRegularExpressions.dll' 
with PERMISSION_SET = SAFE
go

create function RegExpLike(@Text nvarchar(max), @Pattern nvarchar(255), @Options int = 0) 
returns bit 
as external name SqlRegularExpressions.SqlRegularExpressions.[Like]
go

create function RegExpMatches(@text nvarchar(max), @pattern nvarchar(255), @Options int = 0)
returns table ([Index] int, [Length] int, [Value] nvarchar(255))
as external name SqlRegularExpressions.SqlRegularExpressions.GetMatches
go

DbUninstall.sql

drop function RegExpLike
drop function RegExpMatches

drop assembly SqlRegularExpressions
go

sp_configure 'clr enabled', 0
reconfigure
go

Step 3: On model diagram right click, select “Update Model from Database...”, use update wizard to add stored functions to model.

Step 4: Create imported functions in entity context class.

public class TheCompanyContext : Entities
{
        // Please check your entity store name
        [EdmFunction("TheCompanyDbModel.Store", "RegExpLike")]
        public bool RegExpLike(string text, string pattern, int options)
        {
            throw new NotSupportedException("Direct calls are not supported.");
        }
}

Step 5: Finally you can use regular expressions on LINQ to Entities :)

User[] qry = (from u in context.Users
              where u.ApplicationName == pApplicationName
                 && context.RegExpLike(u.Username, usernameToMatch, (int)RegexOptions.IgnoreCase)
              orderby u.Username
              select u)
             .Skip(startIndex)
             .Take(pageSize)
             .ToArray();