问题描述

我在 C# 中使用实体框架，我的代码是

I'm using Entity Framework in C# and my code is

var result = ef.services.Where(entry => entry.tarikhservice >= textBoxX1.Text
                                     && entry.tarikhservice <= textBoxX2.Text).ToList();

这给了我这个错误:

运算符'>='不能应用于'string'和'string'类型的操作数

Operator '>=' cannot be applied to operands of type 'string' and 'string'

如何比较两个字符串并修复错误?

How to compare two string and fix the error?

推荐答案

当你比较数字时，比如 1 和 2，很明显哪个更大.但是，当您比较字符串时，哪个被认为更大:2"还是11"?foo"还是f"?答:这取决于上下文.例如，如果您按字典顺序对它们进行排序，则会得到2"和f".如果你想要自然排序，你会在11"之前得到2".

When you compare numbers, say 1 and 2, it is clear which one is greater. However, when you compare strings, which one is considered greater: "2" or "11"? "foo" or "f"? Answer: it depends on context. For example if you sort them lexicographically, you get "2" and "f". If you want the natural sort, you would get "2" before "11".

我认为出于这个原因，相对运算符(>、>=、<、<=)不会为字符串重载(恕我直言，这是一个不错的决定).

I presume for that reason, relative operators (>, >=, <, <=) are not overloaded for string (which IMHO is a good decision).

您的选择是编写自定义逻辑来比较字符串，或者使用框架提供的字典比较.代码将是(如果我得到正确的数字):

Your option is to either write your custom logic to compare strings, or use a framework-provided lexicographical comparison. The code would be (if I got the numbers right):

var result = ef.services.Where(entry => 
        string.Compare(entry.tarikhservice, textBoxX1.Text) >= 0
     && string.Compare(entry.tarikhservice, textBoxX2.Text) <= 0
   .ToList()

要使代码不受文化影响(你应该！)，提供一个 StringComparison 作为 string.compare 的最后一个参数:

To make code work regardless of culture (you should!), provide a StringComparison as last parameter to string.compare:

string.Compare(entry.tarikhservice, textBoxX1.Text, StringComparison.InvariantCulture)

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