int theId = 33;

// Check if the new exists
var theNew =
    await this.context
        .News
        .FirstAsync(x => x.Id == theId);

// The new doesn't exist
if (theNew == null)
{
    return NotFound();
}

// Check if the user has voted the new
var voted =
    await this.context
        .UserVoteNews
        .FirstAsync(x => x.UserId == this.UserId && x.NewId == theId);

if (voted == null)
{
    return BadRequest(@"User didn't vote");
}
else
{
    return Ok("User voted");
}

using (var dbContextTransaction = this.context.Database.BeginTransaction())

await this.context.SaveChangesAsync();
dbContextTransaction.Commit();