C# LINQ的通配符搜索
我想知道是否可以使用LINQ进行通配符搜索 我看到LINQ有Contains、StartsWith、EndsWith等 如果我想要像%Test这样的东西,如果%it工作,我该怎么做 您可以使用的问候语 用法示例如下:C# LINQ的通配符搜索,c#,sql,linq,wildcard,C#,Sql,Linq,Wildcard,我想知道是否可以使用LINQ进行通配符搜索 我看到LINQ有Contains、StartsWith、EndsWith等 如果我想要像%Test这样的东西,如果%it工作,我该怎么做 您可以使用的问候语 用法示例如下: var results = from u in users where SqlMethods.Like(u.FirstName, "%John%") select u; 您是在对对象使用LINQ还是对SQL使用LINQ 对于LINQ
var results =
from u in users
where SqlMethods.Like(u.FirstName, "%John%")
select u;
您是在对对象使用LINQ还是对SQL使用LINQ
对于LINQ to对象,您必须求助于我的想法。不确定您是使用LinqToSql还是仅使用LINQ。。。但您可以使用如下正则表达式:
.Where(dto => System.Text.RegularExpressions.Regex.IsMatch(dto.CustomerName, @"Ad"));
将System.Data.Linq.SqlClient添加到使用或导入列表中,然后重试:
var results= from x in data
where SqlMethods.Like(x.SearchField, “%something%like%this%”)
select x;
我会使用正则表达式,因为您可能并不总是使用LINQtoSQL 就像这个Linq到对象的例子一样
List<string> list = new List<string>();
list.Add("This is a sentence.");
list.Add("This is another one.");
list.Add("C# is fun.");
list.Add("Linq is also fun.");
System.Text.RegularExpressions.Regex regEx = new System.Text.RegularExpressions.Regex("This");
var qry = list
.Where<string>(item => regEx.IsMatch(item))
.ToList<string>();
// Print results
foreach (var item in qry)
{
Console.WriteLine(item);
}
List List=新列表();
添加(“这是一个句子”);
添加(“这是另一个”);
列表。添加(“C#很有趣。”);
添加(“Linq也很有趣。”);
System.Text.RegularExpressions.Regex Regex=新的System.Text.RegularExpressions.Regex(“此”);
var qry=列表
.Where(item=>regEx.IsMatch(item))
.ToList();
//打印结果
foreach(qry中的var项目)
{
控制台写入线(项目);
}
将同时适用于Linq to SQL和内存中的Linq。在.Net代码(包括Linq to对象)中,我使用的是来自线程的IsSqlLikeMatch函数的实现 使用示例
bool ret = message.IsSqlLikeMatch(pattern);
更多详情请参阅我的帖子
您也可以使用“包含”
我知道这是一个老生常谈的话题,但以下是我非常简单的解决方案:
string s=Regex.Escape("pattern - escaped for sanity").Replace("%", ".*").Replace("_", ".?");
user => Regex.IsMatch(user.FullName, s, RegexOptions.CultureInvariant | RegexOptions.IgnoreCase);
在这段代码中,我为SQL语言使用了常见的转义字符。
如果要使用say*
和?
,转义字符串将相应地包含\*
和\?
,请确保在语句中包含反斜杠字符。替换(…)
语句。
当然,如果您想让您的用户能够进行RexEx搜索,就不要转义模式字符串
搜索Regex教程中的其他选项
我相信正常情况下,%
将至少匹配一个字符,而RegEx*
将匹配零个或多个字符。因此,实际上,%
通配符更像是+
(贪婪)而不是*
(懒惰)
希望这有帮助。看看这个问题 如果我想要像%Test这样的东西,如果%it工作,我该怎么做 那么我期待着一些
LIKE '%Test if%it work%'
这意味着字符串必须按顺序包含“Test if”和“it work”
这是行不通的:
context.SomeTable.Where(s => s.Name.Contains("Test if%it work")).ToList();
如果我使用:
context.SomeTable.Where(s => s.Name.Contains("Test if") && s.Name.Contains("it work")).ToList();
然后,我会找到所有包含“testif”和“it work”的记录,但不是按照那个顺序
因此,这是不可能的。但有了IndexOf它是
IndexOf将定位searchstring并返回它在字符串中的位置。使能按正确的顺序找到单词
--更新--
根据我最初的回答,我的目标不是提供一个通用的解决方案,而是提供一个不依赖sql的另一种方法的示例。因此,原来的例子只回答字面上的问题是正确的。但是,如果答案是泛型的,那么它可能会更有用,因此我编写了一个IQuerable扩展,它允许向查询中添加一个like语句,就像添加where语句一样简单。该扩展既适用于Linq,也适用于LINQSQL
这将按顺序查找所有包含“Test if”和“it work”的记录。
context.SomeTable.Like("test if%it work", "Name").ToList();
listOfString.Like("test if%it work").ToList();
扩展名,允许任意数量的通配符:
/// <summary>
/// Allow to search the string with wildcards.
/// </summary>
/// <typeparam name="T">String or an object with a string member.</typeparam>
/// <param name="q">Original query</param>
/// <param name="searchstring">The searchstring</param>
/// <param name="memberName">The name of the field or null if not a field.</param>
/// <returns>Query filtered by 'LIKE'.</returns>
public static IQueryable<T> Like<T>(this IQueryable<T> q, string searchstring, string memberName = null)
{
// %a%b%c% --> IndexOf(a) > -1 && IndexOf(b) > IndexOf(a) && IndexOf(c) > IndexOf(b)
var eParam = Expression.Parameter(typeof(T), "e");
MethodInfo methodInfo;
// Linq (C#) is case sensitive, but sql isn't. Use StringComparison ignorecase for Linq.
// Sql however doesn't know StringComparison, so try to determine the provider.
var isLinq = (q.Provider.GetType().IsGenericType && q.Provider.GetType().GetGenericTypeDefinition() == typeof(EnumerableQuery<>));
if (isLinq)
methodInfo = typeof(string).GetMethod("IndexOf", new[] { typeof(string), typeof(StringComparison) });
else
methodInfo = typeof(string).GetMethod("IndexOf", new[] { typeof(string) });
Expression expr;
if (string.IsNullOrEmpty(memberName))
expr = eParam;
else
expr = Expression.Property(eParam, memberName);
// Split the searchstring by the wildcard symbol:
var likeParts = searchstring.Split(new char[] { '%' }, StringSplitOptions.RemoveEmptyEntries);
for (int i = 0; i < likeParts.Length; i++)
{
MethodCallExpression e;
if (isLinq)
e = Expression.Call(expr, methodInfo, new Expression[] { Expression.Constant(likeParts[i], typeof(string)), Expression.Constant(StringComparison.OrdinalIgnoreCase) });
else
e = Expression.Call(expr, methodInfo, Expression.Constant(likeParts[i], typeof(string)));
if (i == 0)
{
// e.IndexOf("likePart") > -1
q = q.Where(Expression.Lambda<Func<T, bool>>(Expression.GreaterThan(e, Expression.Constant(-1, typeof(int))), eParam));
}
else
{
// e.IndexOf("likePart_previous")
MethodCallExpression ePrevious;
if (isLinq)
ePrevious = Expression.Call(expr, methodInfo, new Expression[] { Expression.Constant(likeParts[i - 1], typeof(string)), Expression.Constant(StringComparison.OrdinalIgnoreCase) });
else
ePrevious = Expression.Call(expr, methodInfo, Expression.Constant(likeParts[i - 1], typeof(string)));
// e.IndexOf("likePart_previous") < e.IndexOf("likePart")
q = q.Where(Expression.Lambda<Func<T, bool>>(Expression.LessThan(ePrevious, e), eParam));
}
}
return q;
}
//
///允许使用通配符搜索字符串。
///
///字符串或具有字符串成员的对象。
///原始查询
///搜索字符串
///字段的名称,如果不是字段,则为null。
///按“LIKE”筛选的查询。
公共静态IQueryable-Like(此IQueryable q,string searchstring,string memberName=null)
{
//%a%b%c%->IndexOf(a)>-1&&IndexOf(b)>IndexOf(a)&&IndexOf(c)>IndexOf(b)
var eParam=表达式参数(typeof(T),“e”);
方法信息方法信息;
//Linq(C#)区分大小写,但sql不区分大小写。请对Linq使用StringComparison ignorecase。
//但是Sql不知道StringComparison,所以请尝试确定提供程序。
var isLinq=(q.Provider.GetType().IsGenericType&&q.Provider.GetType().GetGenericTypeDefinition()==typeof(EnumerableQuery));
if(isLinq)
methodInfo=typeof(string).GetMethod(“IndexOf”,new[]{typeof(string),typeof(StringComparison)});
其他的
methodInfo=typeof(string).GetMethod(“IndexOf”,new[]{typeof(string)});
表达谱;
if(string.IsNullOrEmpty(memberName))
expr=eParam;
其他的
expr=Expression.Property(eParam,memberName);
//按通配符拆分搜索字符串:
var likeParts=searchstring.Split(新字符[]{“%”,StringSplitOptions.RemoveEmptyEntries);
for(int i=0;i-1
q=q.Where(Expression.Lambda(Expression.GreaterThan(e,Expression.Constant(-1,typeof(int))),eParam));
}
其他的
{
//e.IndexOf(“likePart_previous”)
方法称为前表达;
if(isLinq)
ePrevious=Expression.Call(expr,methodInfo,新表达式[]{Expression.Constant(likeParts[i-1],typeof(string)),Expression.Constant(StringComparison.OrdinalIgnoreCase)});
其他的
ePrevious=Expression.Call(expr,methodInfo,Expression.Constant(likeParts[i-1],typeof(string));
//e.IndexOf(“likePart_previous”)context.SomeTable.Where(s => s.Name.Contains("Test if") && s.Name.Contains("it work")).ToList();
context.SomeTable.Like("test if%it work", "Name").ToList();
listOfString.Like("test if%it work").ToList();
/// <summary>
/// Allow to search the string with wildcards.
/// </summary>
/// <typeparam name="T">String or an object with a string member.</typeparam>
/// <param name="q">Original query</param>
/// <param name="searchstring">The searchstring</param>
/// <param name="memberName">The name of the field or null if not a field.</param>
/// <returns>Query filtered by 'LIKE'.</returns>
public static IQueryable<T> Like<T>(this IQueryable<T> q, string searchstring, string memberName = null)
{
// %a%b%c% --> IndexOf(a) > -1 && IndexOf(b) > IndexOf(a) && IndexOf(c) > IndexOf(b)
var eParam = Expression.Parameter(typeof(T), "e");
MethodInfo methodInfo;
// Linq (C#) is case sensitive, but sql isn't. Use StringComparison ignorecase for Linq.
// Sql however doesn't know StringComparison, so try to determine the provider.
var isLinq = (q.Provider.GetType().IsGenericType && q.Provider.GetType().GetGenericTypeDefinition() == typeof(EnumerableQuery<>));
if (isLinq)
methodInfo = typeof(string).GetMethod("IndexOf", new[] { typeof(string), typeof(StringComparison) });
else
methodInfo = typeof(string).GetMethod("IndexOf", new[] { typeof(string) });
Expression expr;
if (string.IsNullOrEmpty(memberName))
expr = eParam;
else
expr = Expression.Property(eParam, memberName);
// Split the searchstring by the wildcard symbol:
var likeParts = searchstring.Split(new char[] { '%' }, StringSplitOptions.RemoveEmptyEntries);
for (int i = 0; i < likeParts.Length; i++)
{
MethodCallExpression e;
if (isLinq)
e = Expression.Call(expr, methodInfo, new Expression[] { Expression.Constant(likeParts[i], typeof(string)), Expression.Constant(StringComparison.OrdinalIgnoreCase) });
else
e = Expression.Call(expr, methodInfo, Expression.Constant(likeParts[i], typeof(string)));
if (i == 0)
{
// e.IndexOf("likePart") > -1
q = q.Where(Expression.Lambda<Func<T, bool>>(Expression.GreaterThan(e, Expression.Constant(-1, typeof(int))), eParam));
}
else
{
// e.IndexOf("likePart_previous")
MethodCallExpression ePrevious;
if (isLinq)
ePrevious = Expression.Call(expr, methodInfo, new Expression[] { Expression.Constant(likeParts[i - 1], typeof(string)), Expression.Constant(StringComparison.OrdinalIgnoreCase) });
else
ePrevious = Expression.Call(expr, methodInfo, Expression.Constant(likeParts[i - 1], typeof(string)));
// e.IndexOf("likePart_previous") < e.IndexOf("likePart")
q = q.Where(Expression.Lambda<Func<T, bool>>(Expression.LessThan(ePrevious, e), eParam));
}
}
return q;
}
SELECT [Extent1].* FROM SomeTable AS [Extent1]
WHERE ((( CAST(CHARINDEX(N'test if', [Extent1].[Name]) AS int)) - 1) > -1)
AND ((( CAST(CHARINDEX(N'test if', [Extent1].[Name]) AS int)) - 1) <
(( CAST(CHARINDEX(N'it work', [Extent1].[Name]) AS int)) - 1))
var query = from e in _context.Employees
where EF.Functions.Like(e.Title, "%developer%")
select e;
if (!string.IsNullOrEmpty(SearchString))
{
List<String> containValues = new List<String>();
if (SearchString.Contains("*"))
{
String[] pieces = SearchString.Split("*");
foreach (String piece in pieces)
{
if (piece != "")
{
containValues.Add(piece);
}
}
}
if (containValues.Count > 0)
{
foreach(String thisValue in containValues)
{
Items = Items.Where(s => s.Description.Contains(thisValue));
}
}
else
{
Items = Items.Where(s => s.Description.Contains(SearchString));
}
}
public static class LinqLikeExtension
{
/// <summary> Permits searching a string value with any number of wildcards. This was written
/// to handle a variety of EF wildcard queries not supported because the current version is
/// less tan EFv6.2, which has a .Like() method.
/// like in EFv6.</summary>
/// <typeparam name="T">String or an object with a string member.</typeparam>
/// <param name="query">Original query</param>
/// <param name="searchstring">The searchstring</param>
/// <param name="columnName">The name of the db column, or null if not a column.</param>
/// <returns>Query filtered by 'LIKE'.</returns>
/// <example>return iQueryableRows.Like("a", "ReferenceNumber");</example>
/// <example>return iQueryableRows.Like("a%", "ReferenceNumber");</example>
/// <example>return iQueryableRows.Like("%b", "ReferenceNumber");</example>
/// <example>return iQueryableRows.Like("a%b", "ReferenceNumber");</example>
/// <example>return iQueryableRows.Like("a%b%c", "ReferenceNumber");</example>
/// <remarks>Linq (C#) is case sensitive, but sql isn't. Use StringComparison ignorecase for Linq.
/// Keep in mind that Sql however doesn't know StringComparison, so try to determine the provider.</remarks>
/// <remarks>base author -- Ruard van Elburg from StackOverflow, modifications by dvn</remarks>
/// <seealso cref="https://stackoverflow.com/questions/1040380/wildcard-search-for-linq"/>
public static IQueryable<T> Like<T>(this IQueryable<T> query, string searchstring, string columnName = null)
{
var eParam = Expression.Parameter(typeof(T), "e");
var isLinq = (query.Provider.GetType().IsGenericType && query.Provider.GetType().GetGenericTypeDefinition() == typeof(EnumerableQuery<>));
MethodInfo IndexOf, StartsWith, EndsWith, Equals;
MethodCallExpression mceCurrent, mcePrevious;
Expression method = string.IsNullOrEmpty(columnName) ? eParam : (Expression)Expression.Property(eParam, columnName);
var likeParts = searchstring.Split(new char[] { '%' });
for (int i = 0; i < likeParts.Length; i++)
{
if (likeParts[i] == string.Empty) continue; // "%a"
if (i == 0)
{
if (likeParts.Length == 1) // "a"
{
Equals = isLinq
? Equals = typeof(string).GetMethod("Equals", new[] { typeof(string), typeof(StringComparison) })
: Equals = typeof(string).GetMethod("Equals", new[] { typeof(string) });
mceCurrent = isLinq
? Expression.Call(method, Equals, new Expression[] { Expression.Constant(likeParts[i], typeof(string)), Expression.Constant(StringComparison.OrdinalIgnoreCase) })
: Expression.Call(method, Equals, Expression.Constant(likeParts[i], typeof(string)));
}
else // "a%" or "a%b"
{
StartsWith = isLinq
? StartsWith = typeof(string).GetMethod("StartsWith", new[] { typeof(string), typeof(StringComparison) })
: StartsWith = typeof(string).GetMethod("StartsWith", new[] { typeof(string) });
mceCurrent = isLinq
? Expression.Call(method, StartsWith, new Expression[] { Expression.Constant(likeParts[i], typeof(string)), Expression.Constant(StringComparison.OrdinalIgnoreCase) })
: Expression.Call(method, StartsWith, Expression.Constant(likeParts[i], typeof(string)));
}
query = query.Where(Expression.Lambda<Func<T, bool>>(mceCurrent, eParam));
}
else if (i == likeParts.Length - 1) // "a%b" or "%b"
{
EndsWith = isLinq
? EndsWith = typeof(string).GetMethod("EndsWith", new[] { typeof(string), typeof(StringComparison) })
: EndsWith = typeof(string).GetMethod("EndsWith", new[] { typeof(string) });
mceCurrent = isLinq
? Expression.Call(method, EndsWith, new Expression[] { Expression.Constant(likeParts[i], typeof(string)), Expression.Constant(StringComparison.OrdinalIgnoreCase) })
: Expression.Call(method, EndsWith, Expression.Constant(likeParts[i], typeof(string)));
query = query.Where(Expression.Lambda<Func<T, bool>>(mceCurrent, eParam));
}
else // "a%b%c"
{
IndexOf = isLinq
? IndexOf = typeof(string).GetMethod("IndexOf", new[] { typeof(string), typeof(StringComparison) })
: IndexOf = typeof(string).GetMethod("IndexOf", new[] { typeof(string) });
mceCurrent = isLinq
? Expression.Call(method, IndexOf, new Expression[] { Expression.Constant(likeParts[i], typeof(string)), Expression.Constant(StringComparison.OrdinalIgnoreCase) })
: Expression.Call(method, IndexOf, Expression.Constant(likeParts[i], typeof(string)));
mcePrevious = isLinq
? Expression.Call(method, IndexOf, new Expression[] { Expression.Constant(likeParts[i - 1], typeof(string)), Expression.Constant(StringComparison.OrdinalIgnoreCase) })
: Expression.Call(method, IndexOf, Expression.Constant(likeParts[i - 1], typeof(string)));
query = query.Where(Expression.Lambda<Func<T, bool>>(Expression.LessThan(mcePrevious, mceCurrent), eParam));
}
}
return query;
}
}