Linq To Entities将值与List进行比较< int> [英] Linq To Entities Compare Value Against List<int>

问题描述

我正在使用 Entity Framework 5.0 ，并且LINQ查询有问题.我有以下方法，该方法接受一个整数值，然后将其传递到查询中.效果很好.

I am using Entity Framework 5.0, and I have a problem with a LINQ query. I have the following method that accepts an integer value which is then passed into the query. This works fine.

public IList<tblcoursebooking> GetStandardReport(int AttendanceID)
{
    return _UoW.tblcoursebookingRepo.All
           .Where(cb => cb.Attended.Equals(AttendanceID)
           .ToList();

} 

但是，我需要更改方法，以使其接受整数列表，然后提取所有 Attended 等于任何List of的记录.整数.像这样

However, I need to change the method so that it accepts a List of integers, and then pulls out all records where Attended is equal to any of the List of integers. Something like this

public IList<tblcoursebooking> GetStandardReport(List<int> AttendanceIDs)
{
    return _UoW.tblcoursebookingRepo.All
           .Where(cb => cb.Attended.Equals == any AttendanceIDs
           .ToList();
} 

我想尝试使用包含或任何 LINQ关键字，但是，参加是单个值，而不是集合，点后唯一可用的属性是

I would like to do try and use the Contains or Any LINQ keywords, however, as Attended is a single value, not a collection, the only properties available to me after the dot are

CompareTo， 等于， GetHashCode， GetType， GetTypeCode， ToString

CompareTo, Equals, GetHashCode, GetType, GetTypeCode, ToString

有人可以帮忙吗?

感谢您的时间.

推荐答案

使用Contains函数，它将使每个ID与给定列表匹配:

Use the Contains function, it will match each ID against the given list:

return _UoW.tblcoursebookingRepo.All
       .Where(cb => AttendanceIDs.Contains(cb.Attended))
       .ToList();

通常，请记住，Where子句不过是带有嵌套if语句(虽然非常漂亮)的feach foreach.它需要一个计算结果为布尔值的表达式.如果您只需要检查一项而不使用LinQ，就会很快想到:

In general, just keep in mind that a Where clause is nothing more than a fancy foreach with a nested if-statement (a very fancy one, though). It needs an expression that evaluates to a boolean. If you only had one item to check, without using LinQ, you'd quickly come up with something like:

if(AttendanceIDs.Contains(myItem.Attended))

您可以使用完全相同的方式来处理LinQ的Where子句，如上所示:)如果您感到困惑，只需考虑一下如何进行一次检查，因为LinQ会为您完成迭代部分.

You can treat LinQ's Where clauses in exactly the same way, as shown above :) If you're stumped, just think of how you would check it a single time, because LinQ will do the iterative part for you.

更新

如Faisal的回答所述，WhereIn提供了类似的功能.尚未使用过，但似乎是一种更简洁的方法.

As mentioned in Faisal's answer, WhereIn provides a similar functionality. Haven't used it yet, but it seems a more concise approach.

我并没有改变答案，因为我认为更重要的是指出如何在Where子句中使用布尔值评估，这也将有助于解决以后可能遇到的所有类似问题. WhereIn将不相关.

I'm not changing my answer though, as I feel it is more important to point out how you can use the boolean evaluation in a Where clause, this should also help for all future similar issues you might encounter where a WhereIn will not be relevant.

但是，在这种特殊情况下，您也可以使用WhereIn:-)

But nonetheless, you could as well use WhereIn in this particular case :-)

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