Cannot convert implicitly a type 'System.Linq.IQueryable' into 'Microsoft.EntityFrameworkCore.Query.IIncludableQueryable'

I ran into the same issue. Include produces a new abstraction level on top of IQueryable, called IIncludableQueryable. Your var blogging02Context becomes IIncludeQueryable which is not directly assignable from your Where statement.

Declare your blogging02Context variable as IQueryable<Tag> instead of var. It helped in my case.

        IQueryable<Tag> blogging02Context = _context.Tag.Include(t => t.Blog);

        if (!string.IsNullOrEmpty(Urlid.ToString()))
        {
            blogging02Context = blogging02Context.Where(t => t.Urlid == Urlid);
        }

The compile time error is correct as at the first line you have defined the var blogging02Context to _context.Tag.Include(....; This Include method returns Microsoft.EntityFrameworkCore.Query.IIncludableQueryable type. Later, you are adding where clause on the blogging02Context which returns System.Linq.IQueryable.

You can update the code with follows:

However, Another point Urlid is defined as int so this statement if (!string.IsNullOrEmpty(Urlid.ToString())) will never be false; as default value of int would be 0. and 0.ToString() will be "0".

    public async Task<IActionResult> Index(int id, 
    [Bind("Urlid,Userid,UrlStr,Title")] Url blog, int Urlid)
    {
        var blogging02Context = _context.Tag.Include(t => t.Blog).Where(t => t.Urlid == Urlid));

        ViewBag.Urlid = Urlid;
        return View(await blogging02Context.ToListAsync());
    }