C# linq entity-framework linq-to-entities

如何在 Linq-to-Entities 查询中使用 DateTime.AddXXXX 函数？

发布于 2024-12-11 21:21:40 字数 487 浏览 0 评论 0原文

我尝试在查询中使用 AddMonths

List<Entities.Subscriber> items = (from s in context.Subscribers
                 where s.Validated == false && s.ValidationEmailSent == true && s.SubscriptionDateTime < DateTime.Now.AddMonths(-1)
                 select s).ToList();

但收到错误：

LINQ to Entities 无法识别方法“System.DateTime” AddMonths(Int32)'方法，并且该方法不能被翻译成存储表达式。

有没有办法在我的查询中使用这个函数？

原文

I am trying to use AddMonths in a query

List<Entities.Subscriber> items = (from s in context.Subscribers
                 where s.Validated == false && s.ValidationEmailSent == true && s.SubscriptionDateTime < DateTime.Now.AddMonths(-1)
                 select s).ToList();

But I recieve an error :

LINQ to Entities does not recognize the method 'System.DateTime
AddMonths(Int32)' method, and this method cannot be translated into a
store expression.

Is there a way I can use this function inside my query?

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手心的温暖 2024-12-18 21:21:40

对此最简单的解决方法是在使用 LINQ 之前计算出一次时间限制：

DateTime limit = DateTime.Now.AddMonths(-1);

List<Entities.Subscriber> items = (from s in context.Subscribers
             where s.Validated == false && s.ValidationEmailSent == true && 
                                           s.SubscriptionDateTime < limit)
             select s).ToList();

或更易读的 IMO：

var items = context.Subscribers
                   .Where(s => !s.Validated &&
                               s.ValidationEmailSent &&
                               s.SubscriptionDateTime < limit)
                   .ToList();

此处使用查询表达式并与 true 和 false 在我看来是丑陋的（当然，除非你的属性是 Nullable 类型）。

The simplest fix to this is to work out the time limit once before using LINQ:

DateTime limit = DateTime.Now.AddMonths(-1);

List<Entities.Subscriber> items = (from s in context.Subscribers
             where s.Validated == false && s.ValidationEmailSent == true && 
                                           s.SubscriptionDateTime < limit)
             select s).ToList();

Or more readably IMO:

var items = context.Subscribers
                   .Where(s => !s.Validated &&
                               s.ValidationEmailSent &&
                               s.SubscriptionDateTime < limit)
                   .ToList();

There's no benefit in using a query expression here, and explicit comparisons with true and false are ugly IMO (unless your properties are of type Nullable<bool> of course).

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心在旅行 2024-12-18 21:21:40

Jon Skeet 已经提供了一个简单的修复，但如果您希望在数据库上运行 DateTime.Now.AddMonths 位，请尝试 EntityFunctions.AddMonths 方法。

这是一种更通用的方法，当您无法在客户端上廉价或正确地复制表达式时特别有用。

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心意如水 2024-12-18 21:21:40

您可以将代码更改为：

 DateTime oneMonth = DateTime.Now.AddMonths(-1)
    List<Entities.Subscriber> items = (from s in context.Subscribers
                     where s.Validated == false && s.ValidationEmailSent == true && s.SubscriptionDateTime < oneMonth
                     select s).ToList();

您必须这样做，因为 AddMonth 是一个 .NET 函数，无法通过 Linq to Entities 转换为 SQL。在代码中执行计算，然后使用生成的日期时间即可。

You can change your code to:

 DateTime oneMonth = DateTime.Now.AddMonths(-1)
    List<Entities.Subscriber> items = (from s in context.Subscribers
                     where s.Validated == false && s.ValidationEmailSent == true && s.SubscriptionDateTime < oneMonth
                     select s).ToList();

You have to do this because AddMonth is a .NET function that can't be translated into SQL by Linq to Entities. Perform the calculation in your code and then use the resulting datetime will work.

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