Check if property has attribute

user_48684 0
Viewed 137598

Given a property in a class, with attributes - what is the fastest way to determine if it contains a given attribute? For example:

    [IsNotNullable]
    [IsPK]
    [IsIdentity]
    [SequenceNameAttribute("Id")]
    public Int32 Id
    {
        get
        {
            return _Id;
        }
        set
        {
            _Id = value;
        }
    }

What is the fastest method to determine that for example it has the "IsIdentity" attribute?

performance c#
8 Answers

There's no fast way to retrieve attributes. But code ought to look like this (credit to Aaronaught):

var t = typeof(YourClass);
var pi = t.GetProperty("Id");
var hasIsIdentity = Attribute.IsDefined(pi, typeof(IsIdentity));

If you need to retrieve attribute properties then

var t = typeof(YourClass);
var pi = t.GetProperty("Id");
var attr = (IsIdentity[])pi.GetCustomAttributes(typeof(IsIdentity), false);
if (attr.Length > 0) {
    // Use attr[0], you'll need foreach on attr if MultiUse is true
}
nobugz_170340

If you are using .NET 3.5 you might try with Expression trees. It is safer than reflection:

class CustomAttribute : Attribute { }

class Program
{
    [Custom]
    public int Id { get; set; }

    static void Main()
    {
        Expression<Func<Program, int>> expression = p => p.Id;
        var memberExpression = (MemberExpression)expression.Body;
        bool hasCustomAttribute = memberExpression
            .Member
            .GetCustomAttributes(typeof(CustomAttribute), false).Length > 0;
    }
}
Darin_294070

You can use a common (generic) method to read attribute over a given MemberInfo

public static bool TryGetAttribute<T>(MemberInfo memberInfo, out T customAttribute) where T: Attribute {
                var attributes = memberInfo.GetCustomAttributes(typeof(T), false).FirstOrDefault();
                if (attributes == null) {
                    customAttribute = null;
                    return false;
                }
                customAttribute = (T)attributes;
                return true;
            }
user_936130

You can use the Attribute.IsDefined method

https://msdn.microsoft.com/en-us/library/system.attribute.isdefined(v=vs.110).aspx 

if(Attribute.IsDefined(YourProperty,typeof(YourAttribute)))
{
    //Conditional execution...
}

You could provide the property you're specifically looking for or you could iterate through all of them using reflection, something like:

PropertyInfo[] props = typeof(YourClass).GetProperties();
user_11171920
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