Why should you care?

ShopNest “open high-value orders” filters should be reusable in queries and domain checks.

See it live — copy this example

Paste into a C# console or class library project and run dotnet run.

public interface ISpecification<T> { bool IsSatisfiedBy(T candidate); }
public sealed record Order(string Status, decimal Total);
public sealed class OpenOrderSpec : ISpecification<Order>
{
    public bool IsSatisfiedBy(Order o) => o.Status == "Open";
}
public sealed class MinTotalSpec : ISpecification<Order>
{
    private readonly decimal _min;
    public MinTotalSpec(decimal min) => _min = min;
    public bool IsSatisfiedBy(Order o) => o.Total >= _min;
}
public sealed class AndSpec<T> : ISpecification<T>
{
    private readonly ISpecification<T> _a, _b;
    public AndSpec(ISpecification<T> a, ISpecification<T> b) { _a = a; _b = b; }
    public bool IsSatisfiedBy(T c) => _a.IsSatisfiedBy(c) && _b.IsSatisfiedBy(c);
}

var spec = new AndSpec<Order>(new OpenOrderSpec(), new MinTotalSpec(1000));
Console.WriteLine(spec.IsSatisfiedBy(new Order("Open", 2500)));

Run Example »

Edit the code below and click Run to see the result in Toolliyo’s live editor.

What happened?

• Rules become objects you can reuse and combine.
• In EF you often also expose Expression> for SQL translation — covered in the enterprise query lesson.

Practice next

1. Evaluate the sample true/false.
2. Add OrSpec.
3. Reuse OpenOrderSpec in two features.
4. Fail a Closed order.
5. Add CustomerVipSpec.

Remember

Rules as objects. Compose with And/Or. Reuse across app layers.

ShopNest open-order rules

Ops and API share OpenOrderSpec.

Outcome: One definition of “open” everywhere.