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Intentions & Interfaces
Making patterns concrete
Udi Dahan – The Software Simplist
.NET Development Expert & SOA Specialist
www.UdiDahan.com email@UdiDahan.com
Books, and books, and books, and books…
Intentions & Interfaces Making patterns concrete Udi Dahan The - - PowerPoint PPT Presentation
Intentions & Interfaces Making patterns concrete Udi Dahan The - - PowerPoint PPT Presentation
Intentions & Interfaces Making patterns concrete Udi Dahan The Software Simplist .NET Development Expert & SOA Specialist www.UdiDahan.com email@UdiDahan.com Books, and books, and books, and books Flexibility brings many benefits
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Flexibility brings many benefits
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Preventing rigidity from creeping in
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Visitor Pattern Strategy Pattern
Existing solutions
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Visitor pattern
Requires a method for each ConcreteElement
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Strategy pattern
Requires all classes to contain a strategy
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Applicati lication
- n Cod
- de
In Infrastr rastructure ucture Code In Infr fras astructu tructure re Cod
- de
App lic lic at at io ion Co Co de de May cause a collapse of application structure
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Doing too much can hurt
- u
ren„t
- nna
eed t
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“Prediction is very difficult, especially if it's about the future.”
- - Niels Bohr
Physics Nobel prize 1922
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Bolt on flexibility where you need it
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Applicati lication
- n Cod
- de
In Infr frastruc astructure ture Cod
- de
New w Code Code New Code Code
Sometimes called “hooks”
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Flexibility you seek? Hmm? Made your roles explicit, have you? No? That is why you fail.
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Make Roles Explicit
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Some well known interfaces
IFather IHusband IGoToWork IComeHome IWashTheDishes Serializable ISerializable Java
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Custom entity validation before persistence
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The old “object-oriented” way
Cust ustomer
- mer
.Validate();
Order der
.Validate(); *
Ad Address dress
.Validate();
But what if we start here? bool IsValidating;
Persis sistenc ence
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It looks like our
- bjects have
too many roles to play
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Make roles explicit
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IEntity IValidator<T>
ValidationError Validate(T entity); where T : IEntity
Add a marker interface here, and an interface there….
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IEntity Customer Order
The first part is trivial:
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The second part is more interesting
IValidator<T>
ValidationError Validate(T entity);
Customer CustomerValidator: IValidator<Customer>
ValidationError Validate(Customer entity);
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Add a dash of Inversion of Control
Service-Locator style
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The extensible way
.Persist(Customer)
Persis sistenc ence Service vice Lo Loca cator
- r
Cust stomer
- mer Val
alid idat ator
- r
new Validate(Customer) Get<IValidator<Customer>>
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But that’s not Object Oriented Is it?
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Extensible and Object Oriented
.Persist(Customer)
Persis sistenc ence Service vice Lo Loca cator
- r
Cust stomer
- mer Val
alid idat ator
- r
new Validate(Customer) Get<IValidator<Customer>>
Cust stomer
- mer
.Validate();
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And application code stays simple
Applicati lication
- n Cod
- de
In Infr frastruc astructure ture Cod
- de
.Persist(Customer)
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Loading objects from the DB
public class Customer { public void MakePreferred() { foreach(Order o in this.UnshippedOrders) foreach(Orderline ol in o.OrderLines)
- l.Discount(10.Percent);
} } Lazy Loading
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Dangers of Lazy Loading
public void MakePreferred() { foreach(Order o in this.UnshippedOrders) foreach(Orderline ol in o.OrderLines)
- l.Discount(10.Percent);
}
DB
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Loading objects from the DB
Making a customer “preferred” Customer Order OrderLine Adding an Order Customer
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Need Different “Fetching Strategies”
public class ServiceLayer { public void MakePreferred(Id customerId) { Customer c = ORM.Get<Customer>(customerId); c.MakePreferred(); } public void AddOrder(Id customerId, OrderInfo o) { Customer c = ORM.Get<Customer>(customerId); c.AddOrder(o); } }
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Make Roles Explicit
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Use interfaces to differentiate roles
Customer IMakeCustomerPreferred IAddOrdersToCustomer void MakePreferred(); void AddOrder(Order o);
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public class ServiceLayer { public void MakePreferred(Id customerId) { IMakeCustomerPreferred c = ORM .Get< IMakeCustomerPreferred>(customerId); c.MakePreferred(); } public void AddOrder(Id customerId, OrderInfo o) { IAddOrdersToCustomer c = ORM .Get< IAddOrdersToCustomer>(customerId); c.AddOrder(o); } }
Application code specifies role
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Extend behavior around role
Customer IMakeCustomerPreferred IAddOrdersToCustomer void MakePreferred(); void AddOrder(Order o); MakeCustomerPreferredFetchingStrategy :
IFetchingStrategy<IMakeCustomerPreferred> string Strategy { get {
return “UnshippedOrders, OrderLines”; } }
IFetchingStrategy<T>
Inherits T
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The extensible way
.Get<IMakeCustomerPreferred>(id)
Persis sistenc ence Service vice Lo Loca cator
- r
MakeCustomerPreferredFetchingStrategy
new Get strategy Get<IFetchingStrategy< IMakeCustomerPreferred>>
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IMessage IMessageHandler<T>
void Handle(T message); where T : IEntity
And the pattern repeats…
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Once your roles made explicit, you have… Extensibility and flexibility - simple they will be
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Thank you
Udi Dahan – The Software Simplist
.NET Development Expert & SOA Specialist
www.UdiDahan.com email@UdiDahan.com