Specification Pattern Modified (Candidate In Constructor)

Question

I know that design patterns are set by the design and not by specific code yet sometimes I get concerned that I bent the pattern too much and no longer follow the design.

For Example Specification Pattern looks like this:

 public interface ISpecification<T>
{
    bool IsSatisfiedBy(T candidate);
}

But to me this isn't very readable:

 _customerAccountIsActive
.And(_hasReachedRentalThreshold)
.And(_customerAccountHasLateFees)
.IsSatisfiedBy(this);

So I changed it to pass the candidate inside the constructor:

public abstract class Specification<TEntity> : ISpecification<TEntity>
{
    protected TEntity _candidate;

    public Specification(TEntity candidate)
    {
        _candidate = candidate;
    }

    public bool IsSatisfied()
    {
        return IsSatisfiedBy(_candidate);
    }
}

And I even Overloaded The bool operator so I can write something like this:

_customerAccountIsActive 
&& _customerAccountHasLateFees
&& _hasReachedRentalThreshold

Now I'd like to know from someone more experienced with design patterns whether I'm twisting this too much and what are the risks I should be aware of.

I have same question, anybody with experiences comes? – Vu Nguyen Apr 29 '14 at 07:29 — Vu Nguyen, Apr 29 '14 at 07:29

score 1 · Answer 1 · edited May 23 '17 at 11:51

You can find the similar question here How to adapt the Specification pattern to evaluate a combination of objects?. I have same issue with you and there is 2 adaptation I can think.

My problem is comparing 2 object of 2 different type of TEntity in one specification.

Right now, I'm trying to add the second entity to the IsSatisfied(T candidate) like this: IsSatisfied(T firstCandidate, K secondCandidate)

So the Specification will be come Specification, but I think I will lose the ability of combine the Specification with Specification.

So far, I haven't had any good idea about adding second candidate into specification.

There is 2 workarounds that I can think:

Using a parameter object and use this object as an candidate object:

public class ParameterObject<T,K>
{
  public T FirstObject { get; set; }
  public K SecondObject { get; set; {
}


public SomeSpecification: Specification<ParameterObject<Order, Customer>>

public bool IsSatisfied(ParameterObject candidate)
{
   // do some check between order and customer candidates.
}

Using contructor injection:

public class OutOfRangeOrderSpeficiation: Specification<Order>
{
   private ICriteria _criteria;

    public OutOfRangeOrderSpeficiation(ICriteria criteria)
    {
       _criteria = criteria;
    }

    public bool IsSatisfied(Order candidate)
    {
      // comparing between order candidate and _criteria.
      return false;
    }
}

Specification Pattern Modified (Candidate In Constructor)

1 Answers1