c# Process Complex Rules

Question

I have a situation where it is possible for a user to develop complex requirements using a UI. Specifically it deals with authorising users to perform certain work based on their qualifications.

For example the user must have;

1. All of These: Qual1, Qual2, Qual3
   • OR (One of These: (Qual4, Qual5) AND (All of These: Qual11, Qual12, Qual13))
2. AND
   • One or More of These: Qual6, Qual7, Qual8
   • AND One of These: Qual9, Qual10

I've had a look at the Specification Pattern but I'm not sure if this is the best solution for the problem.

The requirements for each role are stored in the database using an Authorisation table linked to a Qualifications table and the user's training via a Training table linked to the Qualifications table.

Answer 1

It seems straightforward to represent such rules in code. To begin with, you're making it way too complicated. "And" and "all of" are both just "all", and "one or more" and "or" are both just "any". So you only need a few predicates:

abstract class Requirement 
{
   abstract public bool Satisfied(User user);
}
sealed class Qual1 : Requirement { ... }
sealed class Qual2 : Requirement { ... }
...
sealed class All : Requirement 
{
   private IEnumerable<Requirement> r;
   public All(params Requirement[] r) { this.r = r; }
   public All(IEnumerable<Requirement> r) { this.r = r; }
   public override bool Satisfied(User user) {
     return r.All(x => x.Satisfied(user));
   }
}
sealed class Any : Requirement 
{
   ....

So now you just have to say:

var q1 = new Qual1();
... etc ...
var rule =  All(
              Any(
                 All(q1, q2, q3), 
                 All(
                     Any(q4, q5), 
                     All(q11, q12, q13))), 
              All(
                Any(q6, q7, q8), 
                Any(q9, q10)));

And now you can say:

if (rule(user)) ...

Easy peasy.