LINQ to objects中是否有SQL IN语句的等效语句?
是的 - 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,这最终变成了一个“IN”查询。var matches = from person in people
join name in desiredNames on person.FirstName equals name
select person;
(当然,这仍然可以使用点号表示法完成,但最终会变得有些混乱。)
在这种情况下,我会选择使用内连接。如果我使用了contains
,即使只有两个匹配项,它也会迭代6次。我想强调的是,我会选择使用连接而不是IN谓词。
var desiredNames = new[] { "Pankaj" };
var people = new[]
{
new { FirstName="Pankaj", Surname="Garg" },
new { FirstName="Marc", Surname="Gravell" },
new { FirstName="Jeff", Surname="Atwood" }
};
var records = (from p in people join filtered in desiredNames on p.FirstName equals filtered select p.FirstName).ToList();