在Linq查询中使用自定义扩展方法

Question

I have made my custom In extension method as shown below:

 public static class ExtensionMethods
    {
        public static bool In(this string str, IEnumerable<String> list)
        {
            foreach (var s in list)
            {
                if (s.Equals(str)) return true; 
            }

            return false; 
        }
    }

And now I like to use it with my LINQ query. What can I do and how do I use it?

Answer 1

I think your method is very similar to Enumerable.Contains. Perhaps you could just use that instead.

If you really want to use your method then it will work fine in a LINQ to Objects query, but it won't be possible to use it in a database query.

Answer 2

You should be able to say

if (stringName.In(listVariableName)){....}

unless the class ExtensionMethods is on a different namespace.