查询即将到来的生日
我想询问我的客户，他们的生日还未到来。
我已经尝试过这个查询，当然 – 它已经失败了：
Addresses.Where(adr => adr.DateOfBirth != null && adr.DateOfBirth.Value > DateTime.Now).Take(15).ToList(); 当然这不能正常工作（如果你将来出生的话），我想知道如何在没有一年的情况下查询我的Nullable ？
你可以在一行中这样做：
context.Addresses.Where(adr => adr.DateOfBirth != null).OrderBy(adr => EntityFunctions.DiffDays(DateTime.Today, EntityFunctions.AddYears(adr.DateOfBirth, EntityFunctions.DiffYears(adr.DateOfBirth, DateTime.Today) + ((adr.DateOfBirth.Month < DateTime.Today.Month || (adr.DateOfBirth.Day <= DateTime.Today.Day && adr.DateOfBirth.Month == DateTime.Today.Month)) ? 1 : 0)))).Take(15).ToList();
或者以更易读的格式：
var query = from adr in context.Addresses where adr.DateOfBirth != null let diffYears = EntityFunctions.DiffYears(adr.DateOfBirth, DateTime.Today) let birthdayOccurred = adr.DateOfBirth.Month < DateTime.Today.Month || (adr.DateOfBirth.Day <= DateTime.Today.Day && adr.DateOfBirth.Month == DateTime.Today.Month) let nextBirthdate = EntityFunctions.AddYears(adr.DateOfBirth, diffYears + (birthdayOccurred ? 1 : 0)) let daysToBirthdate = EntityFunctions.DiffDays(DateTime.Today, nextBirthdate) orderby daysToBirthdate select adr; var result = query.Take(15).ToList();
我不确定你能否做到这一点。 当然没有任何清晰度。
所需的步骤是：
- 创建一个有序列表，其中仅包含今天之后月/日的生日。
- 创建一个有序列表，其中仅包含月/日所在的出生日期。
- 将第二个列表附加到第一个列表，您现在有一个列表，按生日顺序排序。
- 拿第15个。
我认为C＃代码看起来像这样（你可能需要添加一个或两个List。）
var list1 = Addresses.Where(adr => adr.DateOfBirth != null && (adr.DateOfBirth.Value.Month > DateTime.Today.Month || (adr.DateOfBirth.Value.Month == DateTime.Today.Month && adr.DateOfBirth.Value.Day >= DateTime.Today.Day))).ToList(); var list2 = Addresses.Where(adr => adr.DateOfBirth != null && (adr.DateOfBirth.Value.Month < DateTime.Today.Month || (adr.DateOfBirth.Value.Month == DateTime.Today.Month && adr.DateOfBirth.Value.Day < DateTime.Today.Day))).ToList(); var fullList = list1.Add(list2);
尝试这样的事情; （这是有效的 – 我已经测试过了）
//A mock up value for comparison (as DayOfYear not supported in Linq) int doy = DateTime.Today.Month * 31 + DateTime.Today.Day; var results = Addresses.Where(a => a.DateOfBirth != null) .OrderBy( a => (a.DateOfBirth.Value.Month * 31 + a.DateOfBirth.Value.Day) + (a.DateOfBirth.Value.Month * 31 + a.DateOfBirth.Value.Day > doy ? 0 : 400 )) .Take(15).ToList();
我不熟悉Linq，我会尝试帮助一些伪代码。
最重要的条件应如下所示：
Date(CurrentDate.Year, DateOfBirth.Month, DateOfBirth.Day) >= CurrentDate || ' OR Date(CurrentDate.Year + 1, DateOfBirth.Month, DateOfBirth.Day) >= CurrentDate
这将在12月31日也有效。
替代方案：
// consider this as pseudocode, I didnt tested that in C# function GetNextBirthday(DateTime DateOfBirth) { int yearOfNextBirthday; int birthdayMMDD = DateOfBirth.Month*100 + DateOfBirth.Day; int todayMMDD = CurrentDate.Month*100 + CurrentDate.Day; if (birthdayMMDD >= todayMMDD) { yearOfNextBirthday = CurrentDate.Year; // this year } else { yearOfNextBirthday = CurrentDate.Year + 1; // next year } DateTime nextBirthday; // you have to write this line yourself, i dont remember how to make date from Y, M, D nextBirthday = DateFromYMD(yearOfNextBirthday, DateOfBirth.Month, DateOfBirth.Day); return nextBirthday; }
这是我的“一个class轮”的条目：
DateTime now = DateTime.Now; var next15 = from a in db.Addresses where a.DateOfBirth != null let diff = EntityFunctions.DiffSeconds( EntityFunctions.AddYears(now, -EntityFunctions.DiffYears(a.DateOfBirth, now)), a.DateOfBirth) orderby diff >= 0 ? diff : diff + 366*24*60*60 select new a; var res = next15.Take(15).ToList();
刚刚使用SQL数据库进行测试 – 它就像魅力一样;）
这是与@Aducci相同的解决方案，但具有可空日期和DBFunctions，因为EntityFunctions已被弃用。
pacientes = from paciente in pacientes where paciente.Nascimento != null let diffYears = DbFunctions.DiffYears(paciente.Nascimento, DateTime.Today) let birthdayOccurred = paciente.Nascimento.Value.Month < DateTime.Today.Month || (paciente.Nascimento.Value.Day <= DateTime.Today.Day && paciente.Nascimento.Value.Month == DateTime.Today.Month) let nextBirthdate = DbFunctions.AddYears(paciente.Nascimento, diffYears + (birthdayOccurred ? 1 : 0)) let daysToBirthdate = DbFunctions.DiffDays(DateTime.Today, nextBirthdate) orderby daysToBirthdate select paciente;