数据类型linq中存在错误

有一个请求： “带上两个年龄较大（最大年龄）的孩子，完成他们在幼儿园的停留”

“生日”-数据类型=>“日期时间”

错误：DbathmeticExpression参数必须具有数字公共类型

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我哪里出错了

EF不支持对DateTime进行算术运算

var s = db.Child.Max(e => EntityFunctions.DiffDays(DateTime.Today - e.Birthday));

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你把事情复杂化了。最大的孩子是。。。他们是第一个出生的

所以

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从foreach语句中提取where语句并检查数据库数据类型

class Program
{
    static void Main(string[] args)
    {
            List<Test> Tests = new List<Test>();
            Tests.Add(new Test(new DateTime(2014, 01, 01)));
            Tests.Add(new Test(new DateTime(2013, 01, 01)));
            Tests.Add(new Test(new DateTime(2012, 01, 01)));
            Tests.Add(new Test(new DateTime(2011, 01, 01)));
            Tests.Add(new Test(new DateTime(2010, 01, 01)));
            Tests.Add(new Test(new DateTime(2009, 01, 01)));
            Tests.Add(new Test(new DateTime(2008, 01, 01)));


            var s = Tests.Max(e => (DateTime.Today - e.Birthday));
            var d =Tests.Where(e => (DateTime.Today - e.Birthday) == s).Take(2);

    }
}

public class Test
{
    public DateTime Birthday { get; set; }

    public Test(DateTime dateTime)
    {
        Birthday = dateTime;
    }
}

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s

的类型是什么？除非它是一个

TimeSpan

，否则我不会期望

Where

子句有多大意义……非常感谢。但是，什么是错误“System.Data.EntityCommandExecutionException”？它在DeleteObject上吗？您可能需要改用

db.Child.DeleteObject（Child）

var oldestChildren = db.Child.OrderBy(c => c.Birthday).Take(2).ToList();

//if "complete they stay in kindergarten means delete
foreach (var child in oldestChildren)
   db.DeleteObject(child);

class Program
{
    static void Main(string[] args)
    {
            List<Test> Tests = new List<Test>();
            Tests.Add(new Test(new DateTime(2014, 01, 01)));
            Tests.Add(new Test(new DateTime(2013, 01, 01)));
            Tests.Add(new Test(new DateTime(2012, 01, 01)));
            Tests.Add(new Test(new DateTime(2011, 01, 01)));
            Tests.Add(new Test(new DateTime(2010, 01, 01)));
            Tests.Add(new Test(new DateTime(2009, 01, 01)));
            Tests.Add(new Test(new DateTime(2008, 01, 01)));


            var s = Tests.Max(e => (DateTime.Today - e.Birthday));
            var d =Tests.Where(e => (DateTime.Today - e.Birthday) == s).Take(2);

    }
}

public class Test
{
    public DateTime Birthday { get; set; }

    public Test(DateTime dateTime)
    {
        Birthday = dateTime;
    }
}

var oldestChildren = db.Child.OrderBy(c => c.Birthday).Take(2).ToList();