I'm in the process of learning Dapper and I'm having trouble creating instances of anonymous types with it. First of all, some context: we have a method that returns an IEnumerable<T>
. Note that T
can be anonymous.
IEnumerable<T> ExecuteCollection<T>(...)
{
// Query building logic goes here.
var statement = Something.Statement;
var parameters = Something.Parameters;
return _connection.Query<T>(statement, parameters);
}
This code works for registered classes like a charm. However, I want it to handle anonymous types as well, and the problem that is throw by the compiler is:
InvalidOperationException: "A parameterless default constructor or one matching signature ([signature of anonymous object]) is required for <>f__AnonymousType5`2[[System.Int16, System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=XXX],[System.String, System.Private.CoreLib, Version=4.0.0.0, Culture=neutral, PublicKeyToken=XXX]] materialization"
I know that the issue is the fact that anonymous objects have no constructors to work with. An alternative to that would be (T)Activator.CreateInstance(typeof(T), row)
, but the row
variable must be an object[]
, not a DapperRow
.
Whenever I searched for information regarding this topic, everyone said that I shouldn't work with anonymous types to begin with. However, it is required that my function returns a collection of anonymous type items.
This is the first time I'm using Dapper, and I don't know whether I'm misunderstanding things or not. The question is: how can I create an instance of an anonymous object with Dapper, or what is the alternative around this problem so that my method can still return IEnumerable<T>
? I'm using .NET Core.
I think, unless I'm misunderstanding you just want to call
connection.Query(statement, parameters);
Without the generic arguments to do exactly what you are asking for to give you a dapper row. Then you can write
connection.Query(statement, parameters).Select(x => new { Something = x.Something});
To create an anonymous object.
Or to get a little more complicated you could convert to an expando object by casting the row to IDictionary<string,object>
, and iteratively assigning the properties to an expando object.