Store files in database using Entity Framework Core

I am assuming that you are trying to use the windows filestream for sql server, which is not yet supported by .NET Core. You have to store the file as a byte array as already said (which will convert to varbinary(max) in sql server) and copy the file content over when uploading using a memory-stream for instance.

You can convert the file bytes to a byte array.

public byte[] Avatar { get; set; }

Examine the accepted answer in the analogous approach for EF6: Save and retrieve image (binary) from SQL Server using Entity Framework 6