benjaminramey / GoodlyFere.Criteria

General library of specification pattern interfaces and classes to build criteria from.

GoodlyFere.Criteria

General library of specification pattern interfaces and classes to build criteria from.

Example Usage

Encase your business rules in criteria classes (specifications). I recommend making one criteria class for one business rule. You can can combine these rules for more complex logic.

For example, take two Invoice specifications:

public class PastDue : BaseCriteria<Invoice>
{
    public override Expression<Func<T, bool>> Satisfier
    {
        get
        {
            return invoice => invoice.DueDate < DateTime.Now;
        }
    }

    public override void Accept(ICriteriaVisitor<T> visitor)
    {
        visitor.Visit(this);
    }
}

public class Unpaid : BaseCriteria<Invoice>
{
    public override Expression<Func<T, bool>> Satisfier
    {
        get
        {
            return invoice => !invoice.Paid;
        }
    }

    public override void Accept(ICriteriaVisitor<T> visitor)
    {
        visitor.Visit(this);
    }
}

To get all invoices that are past due and unpaid, you can do something like the following:

ICriteria<Invoice> criteria = new PastDue().And(new Unpaid());
IList<Invoice> invoices = new List<Invoice>() {
    new Invoice { DueDate = DateTime.Now.AddDays(-1), Unpaid = true },
    new Invoice { DueDate = DateTime.Now.AddDays(2), Unpaid = false },
    new Invoice { DueDate = DateTime.Now.AddDays(10), Unpaid = true },
};

List<Invoice> pastDueUnpaidInvoices = new List<Invoice>();
foreach(Invoice invoice in invoices)
{
    if (criteria.IsSatisfiedBy(invoice))
    {
        pastDueUnpaidInvoices.Add(invoice);
    }
}

The pastDueUnpaidInvoices list will now contain only the first invoice in this list.

Combining with Repository pattern

I build my repositories with Find methods that take ICriteria<T> classes. I can then use the ICriteria<T>.Satisfier property which is an expression of type Expression<Func<T,bool>> if my data layer supports LINQ for querying.

See this gist for an example repository interface that takes ICriteria<T> parameters for the Find methods.

Version History

• 1.1.0.0: refactor parameter rebinding, add tests, fix ToString infinite recursion bug
• 1.0.3.0: override of ToString method in BaseCriteria
• 1.0.2.0: implemented Accept method in BaseCriteria
• 1.0.0.6: Added .NET 3.5 assembly to nuget package
• 1.0.0.0: initial release, base set of criteria