对于那些像我一样在LINQ中寻找“类似SQL”方法的人来说，我有一些工作得非常好的东西。

我在一个情况下，我不能改变数据库以任何方式改变列排序规则。 所以我必须在LINQ中找到一种方法来做到这一点。

我使用的是辅助方法SqlFunctions。PatIndex的行为类似于真正的SQL LIKE操作符。

首先，我需要枚举搜索值中所有可能的变音符(我刚刚学会的一个词)，以获得类似于:

déjà     => d[éèêëeÉÈÊËE]j[aàâäAÀÂÄ]
montreal => montr[éèêëeÉÈÊËE][aàâäAÀÂÄ]l
montréal => montr[éèêëeÉÈÊËE][aàâäAÀÂÄ]l

然后在LINQ中例如:

var city = "montr[éèêëeÉÈÊËE][aàâäAÀÂÄ]l"; Var data = (from loc in _context.)位置 SqlFunctions的地方。PatIndex(city, loc.City) > 0 选择loc.City) .ToList ();

因此，为了满足我的需求，我写了一个Helper/Extension方法

   public static class SqlServerHelper
    {

        private static readonly List<KeyValuePair<string, string>> Diacritics = new List<KeyValuePair<string, string>>()
        {
            new KeyValuePair<string, string>("A", "aàâäAÀÂÄ"),
            new KeyValuePair<string, string>("E", "éèêëeÉÈÊËE"),
            new KeyValuePair<string, string>("U", "uûüùUÛÜÙ"),
            new KeyValuePair<string, string>("C", "cçCÇ"),
            new KeyValuePair<string, string>("I", "iîïIÎÏ"),
            new KeyValuePair<string, string>("O", "ôöÔÖ"),
            new KeyValuePair<string, string>("Y", "YŸÝýyÿ")
        };

        public static string EnumarateDiacritics(this string stringToDiatritics)
        {
            if (string.IsNullOrEmpty(stringToDiatritics.Trim()))
                return stringToDiatritics;

            var diacriticChecked = string.Empty;

            foreach (var c in stringToDiatritics.ToCharArray())
            {
                var diac = Diacritics.FirstOrDefault(o => o.Value.ToCharArray().Contains(c));
                if (string.IsNullOrEmpty(diac.Key))
                    continue;

                //Prevent from doing same letter/Diacritic more than one time
                if (diacriticChecked.Contains(diac.Key))
                    continue;

                diacriticChecked += diac.Key;

                stringToDiatritics = stringToDiatritics.Replace(c.ToString(), "[" + diac.Value + "]");
            }

            stringToDiatritics = "%" + stringToDiatritics + "%";
            return stringToDiatritics;
        }
    }

如果你们有任何建议来改进这个方法，我很乐意倾听。

如果您需要为单元测试这样的客户端操作提供LIKE功能，CodeProject的这个方法很好地模拟了通配符的行为。

有点像@史蒂夫·阿克曼的回答，但更全面。

/// Published on CodeProject: http://www.codeproject.com/Articles/
///         608266/A-Csharp-LIKE-implementation-that-mimics-SQL-LIKE
/// </remarks>
public static bool Like(this string s, string match, bool CaseInsensitive = true)
{
    //Nothing matches a null mask or null input string
    if (match == null || s == null)
        return false;
    //Null strings are treated as empty and get checked against the mask.
    //If checking is case-insensitive we convert to uppercase to facilitate this.
    if (CaseInsensitive)
    {
        s = s.ToUpperInvariant();
        match = match.ToUpperInvariant();
    }
    //Keeps track of our position in the primary string - s.
    int j = 0;
    //Used to keep track of multi-character wildcards.
    bool matchanymulti = false;
    //Used to keep track of multiple possibility character masks.
    string multicharmask = null;
    bool inversemulticharmask = false;
    for (int i = 0; i < match.Length; i++)
    {
        //If this is the last character of the mask and its a % or * we are done
        if (i == match.Length - 1 && (match[i] == '%' || match[i] == '*'))
            return true;
        //A direct character match allows us to proceed.
        var charcheck = true;
        //Backslash acts as an escape character.  If we encounter it, proceed
        //to the next character.
        if (match[i] == '\\')
        {
            i++;
            if (i == match.Length)
                i--;
        }
        else
        {
            //If this is a wildcard mask we flag it and proceed with the next character
            //in the mask.
            if (match[i] == '%' || match[i] == '*')
            {
                matchanymulti = true;
                continue;
            }
            //If this is a single character wildcard advance one character.
            if (match[i] == '_')
            {
                //If there is no character to advance we did not find a match.
                if (j == s.Length)
                    return false;
                j++;
                continue;
            }
            if (match[i] == '[')
            {
                var endbracketidx = match.IndexOf(']', i);
                //Get the characters to check for.
                multicharmask = match.Substring(i + 1, endbracketidx - i - 1);
                //Check for inversed masks
                inversemulticharmask = multicharmask.StartsWith("^");
                //Remove the inversed mask character
                if (inversemulticharmask)
                    multicharmask = multicharmask.Remove(0, 1);
                //Unescape \^ to ^
                multicharmask = multicharmask.Replace("\\^", "^");
                
                //Prevent direct character checking of the next mask character
                //and advance to the next mask character.
                charcheck = false;
                i = endbracketidx;
                //Detect and expand character ranges
                if (multicharmask.Length == 3 && multicharmask[1] == '-')
                {
                    var newmask = "";
                    var first = multicharmask[0];
                    var last = multicharmask[2];
                    if (last < first)
                    {
                        first = last;
                        last = multicharmask[0];
                    }
                    var c = first;
                    while (c <= last)
                    {
                        newmask += c;
                        c++;
                    }
                    multicharmask = newmask;
                }
                //If the mask is invalid we cannot find a mask for it.
                if (endbracketidx == -1)
                    return false;
            }
        }
        //Keep track of match finding for this character of the mask.
        var matched = false;
        while (j < s.Length)
        {
            //This character matches, move on.
            if (charcheck && s[j] == match[i])
            {
                j++;
                matched = true;
                break;
            }
            //If we need to check for multiple charaters to do.
            if (multicharmask != null)
            {
                var ismatch = multicharmask.Contains(s[j]);
                //If this was an inverted mask and we match fail the check for this string.
                //If this was not an inverted mask check and we did not match fail for this string.
                if (inversemulticharmask && ismatch ||
                    !inversemulticharmask && !ismatch)
                {
                    //If we have a wildcard preceding us we ignore this failure
                    //and continue checking.
                    if (matchanymulti)
                    {
                        j++;
                        continue;
                    }
                    return false;
                }
                j++;
                matched = true;
                //Consumse our mask.
                multicharmask = null;
                break;
            }
            //We are in an multiple any-character mask, proceed to the next character.
            if (matchanymulti)
            {
                j++;
                continue;
            }
            break;
        }
        //We've found a match - proceed.
        if (matched)
        {
            matchanymulti = false;
            continue;
        }

        //If no match our mask fails
        return false;
    }
    //Some characters are left - our mask check fails.
    if (j < s.Length)
        return false;
    //We've processed everything - this is a match.
    return true;
} 

.Where(oh => oh.Hierarchy.Contains("/12/"))

你也可以使用. startswith()或. endswith()。

我假设您正在使用Linq-to-SQL*(参见下面的注释)。如果是，使用字符串。包含字符串。StartsWith和字符串。EndsWith生成使用SQL LIKE操作符的SQL。

from o in dc.Organization
join oh in dc.OrganizationsHierarchy on o.Id equals oh.OrganizationsId
where oh.Hierarchy.Contains(@"/12/")
select new { o.Id, o.Name }

or

from o in dc.Organization
where o.OrganizationsHierarchy.Hierarchy.Contains(@"/12/")
select new { o.Id, o.Name }

注意:* =如果您正在使用ADO。Net实体框架(EF / L2E)，注意它不会像Linq-to-SQL那样进行相同的转换。尽管L2S进行了适当的转换，但L2E v1(3.5)将转换为一个t-sql表达式，该表达式将强制对您正在查询的表进行全表扫描，除非在where子句或连接筛选器中有其他更好的鉴别器。 更新:在EF/L2E v4 (.net 4.0)中修正了这个问题，所以它会像L2S一样生成一个SQL LIKE。

Contains在Linq中使用，就像like在SQL中使用一样。

string _search="/12/";

……

.Where(s => s.Hierarchy.Contains(_search))

你可以像下面这样在Linq中编写SQL脚本:

 var result= Organizations.Join(OrganizationsHierarchy.Where(s=>s.Hierarchy.Contains("/12/")),s=>s.Id,s=>s.OrganizationsId,(org,orgH)=>new {org,orgH});

indexOf也适用于我

var result = from c in SampleList
where c.LongName.IndexOf(SearchQuery) >= 0
select c;