类型'<> f__AnonymousType1`2 [System.String，System.Data.Linq.Binary]'必须声明一个默认（无参数）构造函数

Question

I'm getting the exception

System.InvalidOperationException: The type '<>f__AnonymousType1`2[System.String,System.Data.Linq.Binary]' must declare a default (parameterless) constructor in order to be constructed during mapping.

when I try run

await cmd.ExecuteReaderAsync();

a very simple command that returns rows from a table that contains a rowversion ( timestamp, not null ) column. Any idea why? Very strange.

EDIT:

It's actually failing when I run

return this.Translate<T>(reader);

directly afterwards.

Answer 1

You are getting this error because you are trying to translate your reader in the type that does not have default constructor. That means you have defined your own constructor in the type which overrides the default parameterless constructor.

Simple define the parameter less constructor in the Type in which you are trying to translate the reader object and you are done.