C# 有没有更好的方法来检查 object 中是否有超过 2 个属性不是 null

Question

我正在尝试检查 object 中是否有超过 2 个属性具有值，如果是则返回无效字符串

例子：

Class Student
{
  string Name
  string Code
  string SNumber
}

考虑上面的代码示例，可以编写以下场景

if(studentObj.Name != null && studentObj.Code != null) 
   return "invalid";
if(studentObj.Name != null && studentObj.SNumber != null) 
   return "invalid";
if(studentObj.Code != null && studentObj.SNumber != null) 
   return "invalid";

有没有办法可以简化？

谢谢

Answer 1

你实际上可以数：

class Student
{
  public string Name {get; set;}
  public string Code {get; set;}
  public string SNumber {get; set;}
}

class StudentValidator
{
  public string Validate(Student student)
  {
     int nonZeroCount = 0;
     if( student.Name is object ) nonZeroCount++;
     // in C# 9: if( student.Name is not null )
     if( student.Code is object ) nonZeroCount++;
     if( student.SNumber is object ) nonZeroCount++;
     return (nonZeroCount > 2)? "invalid" : "valid";
  }
}

请注意，您可能更愿意检查

• string.IsNullOrEmtpty(string)或
• string.IsNullOrWhitespace(string)

Answer 2

typeof(Student).GetFields() // use GetProperties() if you have them, and not fields .Select(field => field.GetValue(studentObj) as string) .Count(value => !string.IsNullOrEmpty(value))

Answer 3

在这里，您可以选择优化 select 语句，但作为示例，我提供此选项以供讨论：

class Program
    {
        static void Main(string[] args)
        {
            var students = new List<Student>
            {
                new Student{Name = "Mary",      Code = "1", SNumber = "001" },
                new Student{Name = "Sarah",     Code = "",  SNumber = "002" },
                new Student{Name = "",          Code = "3", SNumber = "003" },
                new Student{Name = "Katherine", Code = "4", SNumber = "004" },
                new Student{Name = "Eva",       Code = "",  SNumber = "" }
            };

            var listedProperty = from student in students
                                  select new List<string> { student.Name, student.Code, student.SNumber };

            listedProperty
                .ToList()
                .ForEach(l =>
                {
                    var nullPropertyCount = l.Count(i => string.IsNullOrWhiteSpace(i));

                    if (nullPropertyCount <= 1)
                    {
                        Console.WriteLine(string.Join(", ", l.ToArray()));
                    }
                });

                Console.ReadLine();
            }
    }

Output 结果到控制台：