C#.NET 4.0:可为空的输入字符串参数和Lambda表达式 [英] c# .net 4.0 : nullable input string parameter and the lambda expressions

问题描述

我有以下方法:

public IQueryable<Profile> FindAllProfiles(string CountryFrom, string CountryLoc)
{


    return db.Profiles.Where(p => p.CountryFrom.CountryName.Equals(CountryFrom,StringComparison.OrdinalIgnoreCase));

}

现在，它仅按CountryFrom进行过滤，但我也需要按CountryLoc进行过滤. 那么，如何修改Where过滤器?

Right now, it just filters by CountryFrom but I need to filter it by CountryLoc as well. So how do I modify the Where filter?

此外，CountryFrom可以为null或CountryLoc可以为null.因此，如何将方法的签名修改为所有可为空的输入字符串参数.

Also, CountryFrom could be null or CountryLoc could be null. So how do I modify the method's signature to all the nullable input string parameter.

我知道如何在SQL中执行此操作，但是我不确定lambda表达式或LINQ.

I know how to do this in SQL but I am not sure about lambda expressions or LINQ.

谢谢

推荐答案

您的问题实际上并非特定于LINQ.您可以将任何布尔条件放入所需的lambda中，例如:

Your question isn't actually LINQ-specific. You can put any boolean conditions inside the lambda that you want, such as:

p => p.CountryFrom.CountryName.Equals(...) && p.CountryLoc.CountryName.Equals(...)

要处理空值，可以改用静态string.Equals方法，如下所示:

To handle null values you can use the static string.Equals method instead, like this:

p => string.Equals(p.CountryFrom.CountryName, CountryName, StringComparison.OrdinalIgnoreCase)

如果开始时间太长，您总是可以将其提取到方法中.

If this starts getting too long you could always extract it into a method.

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