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    public async Task UpdateEmailTable(IEnumerable students)
        Console.WriteLine("Updating Email table");
        var studentEmails = students.ToList();
        int totalStudents = studentEmails.Count;
        int currentCount = 0;
        float lastPercentage = -1;
        foreach (var student in studentEmails)
            var isIn = await _context.BarcDemoGraphicEmail.AnyAsync(z => z.Sridentifier == student.StudentId);
            if (!isIn)
                var ar = await _context.Barcaccount.FirstOrDefaultAsync(z => z.SrIdentifier == student.StudentId);
                await _context.BarcDemoGraphicEmail.AddAsync(new BarcDemoGraphicEmail
                    Sridentifier = student.StudentId,
                    Email = student.EmailAddress,
                    Updatedate = DateTime.Now,
                    Aridentifier = ar == null ? "" : ar.ArIdentifier
                var rec = await _context.BarcDemoGraphicEmail.Where(z => z.Sridentifier == student.StudentId)
                    .FirstAsync();
                rec.Email = student.EmailAddress;
                rec.Updatedate = DateTime.Now;
            await _context.SaveChangesAsync();
            int percentage = (int)Math.Round((float)currentCount / totalStudents * 100);
            if (lastPercentage != percentage) Console.Write("\r" + percentage + "%");
            lastPercentage = percentage;
            currentCount++;
    }

var rec = await _context.BarcDemoGraphicEmail
    .FirstOrDefaultAsync(z => z.Sridentifier == student.StudentId);
if (rec == null)
    var ar = ...

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问 使用LINQ优化数据库访问 EN

回答 2

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