Check if property has attribute

Question

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?

Answer 1

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;     } } 

Answer 2

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 }