你会如何使用LINQ进行"不在"查询？

我不知道这对你有帮助,但是......

NorthwindDataContext dc = new NorthwindDataContext();    
dc.Log = Console.Out;

var query =    
    from c in dc.Customers    
    where !(from o in dc.Orders    
            select o.CustomerID)    
           .Contains(c.CustomerID)    
    select c;

foreach (var c in query) Console.WriteLine( c );

从在LINQ的NOT IN子句中SQL由马可·鲁索

对于以一组内存中对象开头并且正在查询数据库的人,我发现这是最好的方法:

var itemIds = inMemoryList.Select(x => x.Id).ToArray();
var otherObjects = context.ItemList.Where(x => !itemIds.Contains(x.Id));

这WHERE ... IN (...)在SQL中生成一个nice 子句.

第一个列表中第二个列表中不存在电子邮件的项目.

from item1 in List1
where !(list2.Any(item2 => item2.Email == item1.Email))
select item1;

您可以使用Where和Any的组合来查找不在:

var NotInRecord =list1.Where(p => !list2.Any(p2 => p2.Email  == p.Email));

您可以将这两个集合放在两个不同的列表中,例如list1和list2.

然后就写

list1.RemoveAll(Item => list2.Contains(Item));

这会奏效.

在使用ADO.NET实体框架的情况下,EchoStorm的解决方案也可以完美运行.但我花了几分钟时间绕过它.假设您有一个数据库上下文dc,并希望在表x中找不到表y中未链接的行,则完整的答案答案如下所示:

var linked =
  from x in dc.X
  from y in dc.Y
  where x.MyProperty == y.MyProperty
  select x;
var notLinked =
  dc.X.Except(linked);

回答Andy的评论,是的,在LINQ查询中可以有两个来自.这是一个完整的工作示例,使用列表.每个类Foo和Bar都有一个Id.Foo有一个"外键"引用Bar via Foo.BarId.程序选择未链接到相应Bar的所有Foo.

class Program
{
    static void Main(string[] args)
    {
        // Creates some foos
        List fooList = new List();
        fooList.Add(new Foo { Id = 1, BarId = 11 });
        fooList.Add(new Foo { Id = 2, BarId = 12 });
        fooList.Add(new Foo { Id = 3, BarId = 13 });
        fooList.Add(new Foo { Id = 4, BarId = 14 });
        fooList.Add(new Foo { Id = 5, BarId = -1 });
        fooList.Add(new Foo { Id = 6, BarId = -1 });
        fooList.Add(new Foo { Id = 7, BarId = -1 });

        // Create some bars
        List barList = new List();
        barList.Add(new Bar { Id = 11 });
        barList.Add(new Bar { Id = 12 });
        barList.Add(new Bar { Id = 13 });
        barList.Add(new Bar { Id = 14 });
        barList.Add(new Bar { Id = 15 });
        barList.Add(new Bar { Id = 16 });
        barList.Add(new Bar { Id = 17 });

        var linked = from foo in fooList
                     from bar in barList
                     where foo.BarId == bar.Id
                     select foo;
        var notLinked = fooList.Except(linked);
        foreach (Foo item in notLinked)
        {
            Console.WriteLine(
                String.Format(
                "Foo.Id: {0} | Bar.Id: {1}",
                item.Id, item.BarId));
        }
        Console.WriteLine("Any key to continue...");
        Console.ReadKey();
    }
}

class Foo
{
    public int Id { get; set; }
    public int BarId { get; set; }
}

class Bar
{
    public int Id { get; set; }
}