Maybe even preferred.īefore we get into what the pattern is, let’s talk about how things typically are done … You have a class with complicated validation / business rules and you start baking all that into methods in your class – it quickly becomes hard to reason.

No, it’s just part of the overall mechanism.

Do domain experts talk about this process?.

Q: How to tell when a process should be explicit?

Each “process” object represents a different *strategy*.

Make the algorithm, or some key part of it, an object of its own.

A service allows us to express a process explicitly and encapsulate any complex logic within it.īut, what if it can be done in multiple ways?.

So, procedural code in our model right? Well no.

“A lot of design and requirements conversation revolves around the constraints, but in the implementation, they are hidden away in procedural code.”.

“Related rules appear in multiple objects, forcing duplication or inheritance between objects that are not otherwise a family.”.

“Evaluating a constraint requires data that does not otherwise fit the object’s definition.”.

How to know that your class is distorted by constraints

We talked about the Strategy Pattern in episode 16.

This can be done using the Strategy Design Pattern – example in the book uses the overbooking policy from Shipping Cargo p.

If a constraint obscures the objects responsibility, it may be time to factor that constraint out into a separate class or set of classes with relationships.

By giving it an intention-revealing name, others will understand it’s purpose without caring about its implementation.

By giving it a name, we can now discuss it as necessary.

A fundamental concept in MODEL-DRIVEN-DESIGN is that it’s easy to “see” relationships in the model.

Instead of _just_ using the math, instead, put that logic into a specific method.

A constraint can be as simple as a boundary check, i.e.

“ often emerge implicitly, and expressing them explicitly can greatly improve a design.”.

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Grab your Energy Sword – the Halo Championship Series comes to Atlanta –.

Be a thought leader – do tech-talks with your group of developers at your job….

The Order domain object vs the OrderBatch domain object.

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