linq - LINQ to objects 的 In 语句

Question

LINQ to objects 中是否有等效的 SQL IN 语句？

Answer 1

是 - Contains .

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，这最终是一个“IN”查询。)

请注意，在 LINQ to Objects 中，上述内容并不是很有效。你最好加入:

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

(当然，这仍然可以用点表示法来完成，但最终会有些困惑。)