vb.net 在 lambda 表达式中选择多个字段
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Select multiple fields in lambda expression
提问by ruedi
I work through a linq book and just do not understand why
我读了一本 linq 书，只是不明白为什么
customers.where(function(x) x.city = "London").Select(function(y) new with{y.CompanyName, y.Country})
works (creating an anonyomous type, I got that) but
有效（创建一个匿名类型，我明白了）但是
customers.where(function(x) x.city = "London").select(function(y) y.countryname, y.country)
doesnt work. Isnt it possible to select multiple fields in a select query?
不起作用。是否可以在选择查询中选择多个字段？
回答by Tim Schmelter
The reason is: the second is not a valid syntax to create an anonymous type.
原因是：第二个不是创建匿名类型的有效语法。
So this:
所以这：
new with{y.CompanyName, y.Country}
creates an anonymous type with two properties whereas this
创建一个具有两个属性的匿名类型，而 this
y.countryname, y.countr
does create nothing but a compiler error.
除了编译器错误外，什么也不会产生。
It would make sense if you'd create a class Companyand provide a constructor like:
如果您创建一个类Company并提供如下构造函数，那将是有意义的：
Public Class Company
Public Sub New(companyName As String, countryName As String)
Me.Country = countryName
Me.Name = companyName
End Sub
Public Country As String
Public Name As String
End Class
Now you can use this syntax to create an IEnumerable(Of Company):
现在您可以使用此语法创建一个IEnumerable(Of Company)：
Dim companies = customers.
Where(Function(x) x.city = "London").
Select(Function(x) New Company(x.CompanyName, x.Country))
or in query syntax (which i like more in VB):
或查询语法（我更喜欢在 VB 中）：
Dim companies = From c In customers
Where c.City = "London"
Select New Company(c.CompanyName, c.Country)
