在对对象的LINQ声明中 [英] In statement for LINQ to objects

问题描述

LINQ中是否有与对象等效的SQL IN语句?

Is there an equivalent of a SQL IN statement in LINQ to objects?

推荐答案

是-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，这最终以"IN"查询形式出现.)

(In LINQ to SQL this ends up as an "IN" query.)

请注意，在LINQ to Objects中，上述效果并不是很有效.加入联结会更好:

Note that in LINQ to Objects the above isn't really very efficient. You'd be better off with a join:

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

(当然仍然可以使用点符号来完成，但最终会变得更加混乱.)

(This could still be done with dot notation of course, but it ends up being somewhat messier.)

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