c# - What ways can I ensure that a string property is of a particular length?

Question

I've created some classes that will be used to provide data to stored procedures in my database. The varchar parameters in the stored procs have length specifications (e.g. varchar(6) and I'd like to validate the length of all string properties before passing them on to the stored procedures.

Is there a simple, declarative way to do this?

---

I have two conceptual ideas so far:

Attributes

public class MyDataClass
{
     [MaxStringLength = 50]
     public string CompanyName { get; set; }
}

I'm not sure what assemblies/namespaces I would need to use to implement this kind of declarative markup. I think this already exists, but I'm not sure where and if it's the best way to go.

Validation in Properties

public class MyDataClass
{
     private string _CompanyName;
     public string CompanyName
     {
         get {return _CompanyName;}
         set
         {
              if (value.Length > 50)
                  throw new InvalidOperationException();
              _CompanyName = value;
         }
     }
}

This seems like a lot of work and will really make my currently-simple classes look pretty ugly, but I suppose it will get the job done. It will also take a lot of copying and pasting to get this right.

Answer 1

Well, whatever way you go, what's executed is going to look like your second method. So the trick is getting your first method to act your second.

First of all, It would need to be [MaxStringLength(50)]. Next, all that's doing is adding some data to the Type object for this class. You still need a way of putting that data to use.

One way would be a binary re-writer. After compilation (but before execution), the rewriter would read the assembly, looking for that Attribute, and when finding it, add in the code for the check. The retail product PostSharp was designed to do exactly that type of thing.

Alternately, you could trigger it at run-time. SOmething like:

public class MyDataClass 
{ 
     private string _CompanyName;

     [MaxStringLength(50)] 
     public string CompanyName 
     { 
         get {return _CompanyName;} 
         set 
         { 
             ProcessValidation()
              _CompanyName = value; 
         } 
     } 
}

That's still quite ugly, but it's a bit better if you have a number of validation attributes.