Showing User Names (stored in ASP.Net Core Identity system), instead of IDs When loading a table

I've having a lot of trouble doing what you would assume a simple task. Changing user IDs to username when showing a table at my web application. This is the data retrieved form the table:(unnecessary information removed)

var data = (from o in _mainDbContext.blog
                        select new blogViewModel
                        {
                            Id = o.id,
                            title = o.title,
                            Editor= o.editorID,

                        } );

editorID is the user ID created by ASP.Net Identity system. I need to load the corresponding user name and place it inside Editor fields for all the entries fetched.

What I have tried so far:

Something like:

var data = (from o in _mainDbContext.blog
join u in _userManager.Users on o.editorID equals u.UserName
                        select new blogViewModel
                        {
                            Id = o.id,
                            title = o.title,
                            Editor= o.editorID,

                        } );

Doesn't work because EF Core doesn't support joining tables from different contexts.

Using foreach like:

foreach (var row in data)
            {
                var user = await _userManager.FindByIdAsync(row.editorID);
                row.Editor= user.UserName;
            }

Doesn't work. It doesn't change the information inside data.

Trying to use raw SQL did not help either. Because FromSql works only on one table and ExecuteSqlCommand does not work with SELECT.