为什么string.Equals默认情况下不区分大小写？

Question

I have tested the following expressions to evaluate and compare (2) strings:

.Where(x => x.GetAttributeValue<string>("country").Equals("United States"))
.Where(x => x.GetAttributeValue<string>("country").Equals("UNITED STATES"))
.Where(x => x.GetAttributeValue<string>("country").Equals("uniteD sTates"))

NOTE: These queries are expressions built to retrieve data using the CRM LINQ provider from its SDK.

The value of x.GetAttributeValue<string>("country") is exactly United States . All of the expressions above return true . Honestly this is fine and even great with me, but doesn't seem to hold true against the MSDN documentation on string.Equals which states:

This method performs an ordinal (case-sensitive and culture-insensitive) comparison.

I would expect to have to do the following which would ignore overall casing:

.Where(x => x.GetAttributeValue<string>("country").Equals("UnITed sTAtes", StringComparison.OrdinalIgnoreCase))

Interestingly, the above always returns false . To me this is backwards. The default implementation is not taking into account case sensitivity, and the explicit assignment of StringComparison.OrdinalIgnoreCase is acting like it's case sensitive and thus not matching the exact value of United States .

Why is this behavior reverse or am I misunderstanding this?

Answer 1

Are you using LINQ-To-Sql? If so, that code is actually building an expression tree that is then translated into SQL statements that are run on Sql Server. Sql Server, like most database engines, does not care about case by default.

If this were Linq-To-Objects, I expect you'd get different results.

Answer 2

Actually, all LINQ expressions against CRM context is converted by LINQ provider to QueryExpression . And string.Equals filter is defined there as case insensitive, so you get this result.

About your attempt with StringComparison.OrdinalIgnoreCase , IMO it could be (and I think it is) that the provider does not support that method with a second parameter (I've tried and it does not return desired result with other comparison types either).

Answer 3

You may try to use

x.GetAttributeValue<string>("country") == "United States"

instead of

x.GetAttributeValue<string>("country").Equals("United States")