Untyped serializer and complex types (class or struct)

[bellons91]

Issue description

I'm experimenting with this library to work with dynamic columns.

Using the untyped serializer, I'm trying to work with complex types.

I want one of the fields to represent a dummy structure, User. It can either be a struct or a class: it's not important as long as I can access its fields.

User as a Class

I tried to define User as a class

public class User {
     public string Name { get; set; }
}

I tried defining the ParquetSchema like this:

private readonly ParquetSchema schema = new (
     new DataField<string>("Customer")
     , new DataField<User>("User")
);

and like this:

private readonly ParquetSchema schema = new (
      new DataField<string>("Customer")
      , new DataField("User", typeof(User))
);

But, when I run the application, I get the following exception.

System.NotSupportedException: 'type Scripts.General.ParquetReadWriteWithDynamicFields+User is not supported'

User as a Struct

I then tried defining it as a struct:

public struct User {
    public string Name { get; set; }
}

Again, same exception:

System.NotSupportedException: 'type Scripts.General.ParquetReadWriteWithDynamicFields+User is not supported'

Another approach: use the StructField, as described here.

private readonly ParquetSchema schema = new (
  new DataField<string>("Customer")
  , new StructField("User", new DataField<string>("Name"))
);

Now the schema is well defined, but when serializing an object this way:

using (var fs = File.Create(FilePath))
{
    await ParquetSerializer.SerializeAsync(
        schema: schema,
        data: items
        destination: fs,
        options: options);
}

I get the following exception:

System.ApplicationException: 'failed to serialise data column 'User/Name
InvalidCastException: Unable to cast object of type 'User' to type 'System.Collections.Generic.IDictionary`2[System.String,System.Object]'.

Am I defining the schema in the wrong way? Or maybe, now that I'm serializing subtypes, I have to use the ParquetRowGroupWriter described in the documentation?