Add bool attribute on property to see if we need to check for null

Question

User-1188570427 posted

Is it possible to add an attribute on a property to check if I need to check that property for being Null or string empty?

Then I can pass it to the AllPropertiesValid() method and if the attribute is TRUE then I need to check, if FALSE then ignore and by pass it.

Thank you.

    public class MyDto
    {
        public string Prop1 { get; set; }
        public int? Prop2 { get; set; }

    }

        public static bool AllPropertiesValid(object obj)
        {
            return !obj.GetType().GetProperties().All(p =>
            {
                var value = p.GetValue(obj);

                if (value == null) { return false; }

                if (p.PropertyType == typeof(string))
                {
                    return string.IsNullOrEmpty((string)value);
                }

                if (p.PropertyType == typeof(int))
                {
                    return ((int)value <= 0);
                }

                if (p.PropertyType == typeof(bool))
                {
                    return (!(bool)value);
                }

                if (p.PropertyType == typeof(Guid))
                {
                    return ((Guid)value) == Guid.Empty;
                }

                return true;
            });
        }

Answer 1

User753101303 posted

Hi,

You mean https://docs.microsoft.com/en-us/dotnet/api/system.componentmodel.dataannotations.requiredattribute?view=netframework-4.7.2 and other annotations ?

It is validated for you. It doesn't seems you would need to write your own code.

Answer 2

User-893317190 posted

Hi tvb2727,

If you want to use you customized attribute, you could try the code below.

My attribute.

 [AttributeUsage(AttributeTargets.Property)]
    public class NeedCheckAttribute:Attribute
    {
        public bool needCheck { get; set; }
        public NeedCheckAttribute(bool needCheck)
        {
            this.needCheck = needCheck;
        }
    }

My model

 public class MyDto
    {
        [NeedCheck(true)]
        public string Prop1 { get; set; }
        [NeedCheck(false)]
        public int? Prop2 { get; set; }
        [NeedCheck(true)]
        public bool? Prop3 { get; set; }
        [NeedCheck(false)]
        public Guid Prop4 { get; set; }
    }

My test code.

  protected void Page_Load(object sender, EventArgs e)
        {
            TestAttribute(new MyDto());
        }

        public static void TestAttribute(Object obj)
        {
            var t = obj.GetType();
            var properties = t.GetProperties();
            foreach (var item in properties)
            {
// if the property has NeedCheck attribute
                if (item.IsDefined(typeof(NeedCheckAttribute), false))
                {
// get the NeedCheck attribute
                    var attribute = item.GetCustomAttributes(typeof(NeedCheckAttribute), false).First();
// get the value the needCheck property
                   bool flag= (bool)attribute.GetType().GetProperty("needCheck").GetValue(attribute);
//    and you could apply your own validation according to the value of flag
                    HttpContext.Current.Response.Write(item.Name+":"+flag+"<br/>");
                }
            }
        }

The result.

Best regards,

Ackerly Xu