查询即将到来的生日 [英] Query upcoming birthdays

问题描述

我想向我的顾客查询那些生日还没到的顾客.

I'd like to query my customers for the ones, whose birthdays are yet to come.

我已经尝试过该查询，但是它当然失败了:

I've tried this query, and it - of course - has failed breathtakingly:

Addresses.Where(adr => adr.DateOfBirth != null && adr.DateOfBirth.Value >
DateTime.Now).Take(15).ToList();

这当然不能正常工作(如果您将来出生的话就不能)，我想知道如何在没有一年的时间查询我的Nullable<DateTime>?

Of course this can't work properly (not if you're born in the future) and I'd like to know how I can query my Nullable<DateTime> without a year?

推荐答案

您可以像这样在一行中完成此操作:

You can do it in one line like this:

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();

或更可读的格式:

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();

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