Map from HttpPostedFileBase to Byte[] with automapper

Question

Im trying to upload a picture and use automapper to convert it from HttpPostedFileBase to Byte[]. This is my CreateMap:

            Mapper.CreateMap<HttpPostedFileBase, Byte[]>()
            .ForMember(d => d, opt => opt.MapFrom(s => 
                {
                    MemoryStream target = new MemoryStream();
                    s.InputStream.CopyTo(target);
                    return target.ToArray();
                }));

I get an error on s : A lambda expression with a statement body cannot be converted to an expression tree.

So how should i write my CreateMap to get this to work?

Answer 1

There are at least two ways to do this:

1. Use a custom type converter:

   public class HttpPostedFileBaseTypeConverter : 
       ITypeConverter<HttpPostedFileBase, byte[]>
   {
       public byte[] Convert(ResolutionContext ctx)
       {
           var fileBase = (HttpPostedFileBase)ctx.SourceValue;
   
           MemoryStream target = new MemoryStream();
           fileBase.InputStream.CopyTo(target);
           return target.ToArray();        
       }
   }
   

   Usage:

   Mapper.CreateMap<HttpPostedFileBase, byte[]>()
       .ConvertUsing<HttpPostedFileBaseTypeConverter>();
   

2. Use ConstructUsing and do it inline:

   Mapper.CreateMap<HttpPostedFileBase, byte[]>()
       .ConstructUsing(fb =>
   {
       MemoryStream target = new MemoryStream();
       fb.InputStream.CopyTo(target);
       return target.ToArray();
   });
   

Answer 2

This is not the best way to read bytes from a file upload because IIS allocates the entire size of the uploading file when the uploading process starts. Then your mapper allocates another similar size of bytes (byte[] array is a new variable) and the overall memory usage is going to be file bytes * 2.

My advice is to read the posted file stream and to write it somewhere. You can do any post-upload processing after uploading.