Dapper and object validation/business rules enforcement

Question

This isn't really Dapper-specific, actually, as it relates to any XML-serializeable object.. but it came up when I was storing an object using Dapper.

Anyways, say I have a user class. Normally, I'd do something like this:

class User
{
    public string SIN {get; private set;}
    public string DisplayName {get;set;}

    public User(string sin)
    {
        if (string.IsNullOrWhiteSpace(sin))
            throw new ArgumentException("SIN must be specified");
        this.SIN = sin;
    }
}

Since a SIN is required, I'd just create a constructor with a sin parameter, and make it read-only.

However, with a Dapper (and probably any other ORM), I need to provide a parameterless constructor, and make all properties writeable. So now I have this:

class User: IValidatableObject 
{
    public int Id { get; set; }
    public string SIN { get; set; }
    public string DisplayName { get; set; }

    public IEnumerable<ValidationResult> Validate(ValidationContext validationContext)
    {
      // implementation
    }
}

This seems.. can't really pick the word, a bad smell?
A) I'm allowing to change properties that should not be changed ever after an object has been created (SIN, userid)

B) Now I have to implement IValidatableObject or something like that to test those properties before updating them to db.

So how do you go about it ?

Answer 1

Generally speaking, your database is going to assign the ID on an insert operation, not you. If you fail to provide the ID for an read, edit or delete operation, the operation will simply not work. In other words, the database is performing the validation on the ID, not your DTO class.

Often, DTO classes are populated by some automated process, either by reading from a database, binding to a web form, or deserialization. All of the fields are populated simultaneously. There's no way to tell, ahead of time, whether the ID is going to be populated properly. That's why the validation is done after the fact.