C# LINQ - FirstOrDefault() 然后 Select()
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LINQ - FirstOrDefault() then Select()
提问by Simon
I have the following LINQ query that fires and exception when the FirstOrDefault()returns null. Ideally I would like to avoid the null check. Is there a way to do this? I wish to return 0if there are no CPOffsetsthat satisfy the FirstOrDefault()call.
我有以下 LINQ 查询，当FirstOrDefault()返回空值时会触发和异常。理想情况下，我想避免空检查。有没有办法做到这一点？0如果没有CPOffsets满足FirstOrDefault()要求，我希望返回。
double offset = OrderedOffsets.FirstOrDefault(o => o.OffsetDateTime > cpTime).CPOffset;
The only way I can see to achieve this is the following:
我可以看到实现这一目标的唯一方法如下：
CPOffset cpOffset = OrderedOffsets.FirstOrDefault(o => o.OffsetDateTime > cpTime);
double offset = cpOffset != null ? cpOffset.CPOffset : 0;
Is there another more succinct way? Using Select()after the FirstorDefault()doesn't compile but I thought might be appropriate here?
还有其他更简洁的方法吗？Select()在FirstorDefault()不编译后使用，但我认为在这里可能合适？
采纳答案by NSGaga-mostly-inactive
I think this should work, I'm not near by VS to check it out...
我认为这应该有效，我不在 VS 附近检查一下...
OrderedOffsets.Where(o => o.OffsetDateTime > cpTime).Select(x => x.CPOffset).FirstOrDefault();
回答by Servy
DefaultIfEmptycan be used to ensure that the collection always has at least one element.
DefaultIfEmpty可用于确保集合始终至少有一个元素。
double offset = OrderedOffsets.Where(o => o.OffsetDateTime > cpTime)
.Select(o => o.CPOffset)
.DefaultIfEmpty()
.First();
回答by Romain
I think a good pattern could be :
我认为一个好的模式可能是：
double offset = (OrderedOffsets.FirstOrDefault(o => o.OffsetDateTime > cpTime) ?? someDefaultObject).CPOffset;
with someDefaultObjectan object holding default values... With this pattern, you can change easily you default values through your code !
使用someDefaultObject保存默认值的对象...使用此模式，您可以通过代码轻松更改默认值！
If OrderedOffsets can be a struct you could also just put your default value there ! :)
如果 OrderedOffsets 可以是一个结构，您也可以将默认值放在那里！:)
