为什么EnumerableRowCollection< DataRow> .Select()不能这样编译? [英] Why doesn't EnumerableRowCollection<DataRow>.Select() compile like this?

问题描述

这有效:

from x in table.AsEnumerable()
where x.Field<string>("something") == "value"
select x.Field<decimal>("decimalfield");

但是，这不是:

from x in table.AsEnumerable()
.Where(y=>y.Field<string>("something") == "value")
.Select(y=>y.Field<decimal>("decimalfield"));

我也尝试过:

from x in table.AsEnumerable()
.Where(y=>y.Field<string>("something") == "value")
.Select(y=>new { name = y.Field<decimal>("decimalfield") });

看着.Select()方法的两个重载，我认为后两个应该都返回EnumerableRowCollection，但是显然我错了.我想念什么?

Looking at the two overloads of the .Select() method, I thought the latter two should both return EnumerableRowCollection, but apparently I am wrong. What am I missing?

推荐答案

问题是您正在组合两种执行linq查询的方法(查询语法和直接调用linq扩展方法).第from x in table.AsEnumerable()行不是有效的查询，因为它至少需要一个select ....这应该起作用:

The problem is you're combining two ways of performing a linq query (query syntax and calling the linq extension methods directly). The line from x in table.AsEnumerable() is not a valid query since it require at least a select .... This should work:

table.AsEnumerable() 
.Where(y=>y.Field<string>("something") == "value") 
.Select(y=>new { name = y.Field<decimal>("decimalfield") });

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