Use extension method for selecting in EF Core

Question

I want to use extension methods for selecting from tables so I don't have to keep entering the fields. The problem is that when I use select directly everything is fine, but when I use the extension method, I get all sorts of errors on runtime.

This is my Media entity:

[Table("Media")]
public class MediaEntity : BaseEntity 
{
    [StringLength(500)]
    public string? FileName { get; set; }

    [StringLength(500)]
    public string? UseCase { get; set; }

    [StringLength(500)]
    public string? Link { get; set; }

    [StringLength(500)]
    public string? Title { get; set; }

    [StringLength(500)]
    public string? Size { get; set; }

    [StringLength(500)]
    public string? Time { get; set; }

    [StringLength(500)]
    public string? Artist { get; set; }

    [StringLength(500)]
    public string? Album { get; set; }
}

Here is my MediaReadDto:

public class MediaReadDto : BaseEntity 
{
        public string? FileName { get; set; }
        public string? UseCase { get; set; }
        public string? Link { get; set; }
        public string? Title { get; set; }
        public string? Size { get; set; }
        public string? Time { get; set; }
        public string? Artist { get; set; }
        public string? Album { get; set; }
}

And here is my select extension method:

public static class MediaEntityExtension 
{
    public static IEnumerable<MediaReadDto> MapContentReadDto(this IEnumerable<MediaEntity> e) 
    {
        return e.Select(y => new MediaReadDto 
                                 {
                                     Link = y.Link,
                                     UseCase = y.UseCase,
                                     Album = y.Album,
                                     Artist = y.Artist,
                                     Size = y.Size,
                                     Time = y.Time,
                                     Title = y.Title,
                                     FileName = y.FileName
                                 });
    }
}

And this is where I use my extension method:

e.Select(x => new ContentReadDto {
            Id = x.Id,
            Title = x.Title,
            Type = x.Type,
            UseCase = x.UseCase,
            Media = x.Media!.MapContentReadDto()
        })

The errors I get:

System.ArgumentException: GenericArguments[1], 'System.Collections.Generic.IEnumerable1[Utilities_aspnet.Entities.MediaEntity]', on 'TCollection InitializeSplitCollection[TElement,TCollection](Int32, Microsoft.EntityFrameworkCore.Query.QueryContext, System.Data.Common.DbDataReader, Microsoft.EntityFrameworkCore.Query.Internal.SplitQueryResultCoordinator, System.Func3[Microsoft.EntityFrameworkCore.Query.QueryContext,System.Data.Common.DbDataReader,System.Object[]], Microsoft.EntityFrameworkCore.Metadata.IClrCollectionAccessor)' violates the constraint of type 'TCollection'.