maxlength attribute of a text box from the DataAnnotations StringLength in Asp.Net MVC

Question

I am working on an MVC2 application and want to set the maxlength attributes of the text inputs.

I have already defined the stringlength attribute on the Model objec

Answer 1

Here are some static methods you can use to get the StringLength, or any other attribute.

using System;
using System.Linq;
using System.Reflection;
using System.ComponentModel.DataAnnotations;
using System.Linq.Expressions;

public static class AttributeHelpers {

public static Int32 GetStringLength(Expression> propertyExpression) {
    return GetPropertyAttributeValue(propertyExpression,attr => attr.Length);
}

//Optional Extension method
public static Int32 GetStringLength(this T instance,Expression> propertyExpression) {
    return GetStringLength(propertyExpression);
}


//Required generic method to get any property attribute from any class
public static TValue GetPropertyAttributeValue(Expression> propertyExpression,Func valueSelector) where TAttribute : Attribute {
    var expression = (MemberExpression)propertyExpression.Body;
    var propertyInfo = (PropertyInfo)expression.Member;
    var attr = propertyInfo.GetCustomAttributes(typeof(TAttribute),true).FirstOrDefault() as TAttribute;

    if (attr==null) {
        throw new MissingMemberException(typeof(T).Name+"."+propertyInfo.Name,typeof(TAttribute).Name);
    }

    return valueSelector(attr);
}

}

Using the static method...

var length = AttributeHelpers.GetStringLength(x => x.Address1);

Or using the optional extension method on an instance...

var player = new User();
var length = player.GetStringLength(x => x.Address1);

Or using the full static method for any other attribute...

var length = AttributeHelpers.GetPropertyAttributeValue(prop => prop.Address1,attr => attr.MaximumLength);

Inspired by the answer here... https://stackoverflow.com/a/32501356/324479