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var v = connection.Query(@"select 1 A,2 B ");
var cV = v as IEnumerable<IDictionary<string,object>>;
Console.WriteLine(v.GetType().FullName); // result : System.Collections.Generic.List`1[[Dapper.SqlMapper+DapperRow, Dapper, Version=2.0.0.0, Culture=neutral, PublicKeyToken=null]]
Console.WriteLine(cV); // result : A=1,B=2
var v = connection.Query(@"select 1 A,2 B ").ToList();
var cV = v as IEnumerable<IDictionary<string, object>>;
Console.WriteLine(v.GetType().FullName); // result : System.Collections.Generic.List`1[[System.Object, System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]]
Console.WriteLine(cV); // result : null
My question is :
Dapper Query as
IEnumerable<IDictionary<string,object>>
is not null
, but why after ToList then as
IEnumerable<IDictionary<string,object>>
is null
As I know List is extends by
IEnumerable<T>
so Dapper Query ToList Should be
IEnumerable<IDictionay<string,object>>
but result is not.
public class List<T> : IList<T>, ICollection<T>, IEnumerable<T>, IEnumerable, IList, ICollection, IReadOnlyList<T>, IReadOnlyCollection<T>
update:
And It's work if specify IDictionary<string,object> type in foreach
var v = connection.Query(@"select 1 A,2 B ").ToList();
foreach (IDictionary<string, object> e in v)
Console.WriteLine(v.GetType().FullName); // result : System.Collections.Generic.List`1[[System.Object, System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e]]
Console.WriteLine(e); // result : A=1,B=2
–
The return type of Query with no generic type argument is IEnumerable<dynamic>, the actual object is a List<DapperRow>.
DapperRow happens to implement IDictionary<string, object>. Therefore:
In version 1 of your code you can cast the List directly to IEnumerable<IDictionary<string, object>.
Version 2 you are calling ToList, but because you haven't got the exact type, you end up with a call to ToList<object>. Remember, ToList always creates a new list, even when the existing object is a list already.
Your final version goes back to the original, but now it casts each object in the list to IDictionary<string, object>. So it is equivalent to the following code:
foreach (var e in v.Cast<IDictionary<string, object>())
Personally I always use actual classes with Query<MyClass> and I don't rely on dynamic or DapperRow as it can be inefficient and difficult to use.
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