LINQ 中的 LIKE 运算符 [英] LIKE operator in LINQ

问题描述

有什么方法可以比较类似于 SQL 的 LIKE 运算符的 C# LINQ 表达式中的字符串?

Is there any way to compare strings in a C# LINQ expression similar to SQL's LIKE operator?

假设我有一个字符串列表.在这个列表中，我想搜索一个字符串.在 SQL 中，我可以这样写:

Suppose I have a string list. On this list I want to search a string. In SQL, I could write:

SELECT * FROM DischargePort WHERE PortName LIKE '%BALTIMORE%'

与上面的不同，查询需要 linq 语法.

Instead of the above, query want a linq syntax.

using System.Text.RegularExpressions;
…

var regex = new Regex(sDischargePort, RegexOptions.IgnoreCase);
var sPortCode = Database.DischargePorts
                .Where(p => regex.IsMatch(p.PortName))
                .Single().PortCode;

我上面的 LINQ 语法不起作用.我做错了什么?

My above LINQ syntax does not work. What have I got wrong?

推荐答案

通常使用 String.StartsWith/EndsWith/Contains.例如:

Typically you use String.StartsWith/EndsWith/Contains. For example:

var portCode = Database.DischargePorts
                       .Where(p => p.PortName.Contains("BALTIMORE"))
                       .Single()
                       .PortCode;

我不知道是否有办法通过 LINQ to SQL 执行正确的正则表达式.(请注意，它确实取决于您使用的提供程序 - 在 LINQ to Objects 中会很好；这是提供程序是否可以将调用转换为其本机查询格式，例如 SQL.)

I don't know if there's a way of doing proper regular expressions via LINQ to SQL though. (Note that it really does depend on which provider you're using - it would be fine in LINQ to Objects; it's a matter of whether the provider can convert the call into its native query format, e.g. SQL.)

正如 BitKFu 所说，Single 应该在您期望 恰好一个 结果时使用 - 当情况并非如此是错误时.SingleOrDefault、FirstOrDefault 或 First 的选项应该根据正是的预期使用.

As BitKFu says, Single should be used when you expect exactly one result - when it's an error for that not to be the case. Options of SingleOrDefault, FirstOrDefault or First should be used depending on exactly what's expected.

这篇关于LINQ 中的 LIKE 运算符的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！