Question

public interface IRule
{
    bool Check(string input);
}

I have an interface that defines a rule. A rule is just a generic business rule or constraint that a user can create. So I have two sample rules:

public class ContainsRule : IRule
{
    public string MustContain { get; set; }

    public bool Check(string input)
    {
        return input.Contains(this.MustContain);
    }
}

public class LengthRule : IRule
{
    public int MaxLength { get; set; }

    public bool Check(string input)
    {
        return input.Length <= this.MaxLength;
    }
}

Rules may have more than one property that can be set, but in this example, each of these rules only have one property.

A user can create their own set of rules that should be saved. For example, a user have these three rules:

IRule[] rules = new IRule[]
{
    new ContainsRule { MustContain = "foo" },
    new ContainsRule { MustContain = "bar" },
    new LengthRule { MaxLength = 5}
};

I need to persist this information to a database or some data store for each user. Since each user can have their own set of rules, I’m not sure what the database tables should look like.

User  |  ClassName               |  Parameters
-----------------------------------------------
1     |  Namespace.ContainsRule  |  MustContain:foo
1     |  Namespace.ContainsRule  |  MustContain:bar
1     |  Namespace.LengthRule    |  MaxLength:5

My initial guess would be to create a table that looks something like the above, where parameters should a string. This means I would need to parse out the information and use reflection or something to set the properties. I would need to use the activator to create the class using the ClassName column. Another suggestion was instead of creating a delimited string for all the properties, there would be another table. Each of the properties would be its own row that has a foreign key relationship back to a row in the table above.

However, both examples don’t seem to be the best way of saving these rules. Is there a better way to do this?

Answer 1

Why not use XML serialisation. The database table would contain the User # and the XML serialisation of the indvidual rule.