在LINQ to对象的语句中

Question

在LINQ对象中是否有等效的SQL IN语句？

Answer 1

是的 - 包含.

var desiredNames = new[] { "Jon", "Marc" };

var people = new[]
{
    new { FirstName="Jon", Surname="Skeet" },
    new { FirstName="Marc", Surname="Gravell" },
    new { FirstName="Jeff", Surname="Atwood" }
};

var matches = people.Where(person => desiredNames.Contains(person.FirstName));

foreach (var person in matches)
{
    Console.WriteLine(person);
}

(在LINQ to SQL中,这最终成为"IN"查询.)

请注意,在LINQ to Objects中,上面的效率并不高.加入你会更好:

var matches = from person in people
              join name in desiredNames on person.FirstName equals name
              select person;

(当然,这仍然可以通过点符号来完成,但最终会有些麻烦.)