solid - not just a state of matter, its principles for oo propriety

SOLIDNot Just a State of Matter, It’s Principles for OO Propriety

Chris Weldon

Me

• Fightin’ Texas Aggie

• .Net and PHP Developer

• UNIX and Windows Sysadmin

• Senior Consultant at Improving Enterprises

• Contact Me: [email protected]

mailto:[email protected]


Agile, Microsoft, Open Technologies, UX

Applied Training, Coaching, Mentoring

Certified Consulting

Rural Sourcing

Recruiting Services

What is OOD?

What is OOD?

Abstraction

What is OOD?

InheritanceAbstraction

What is OOD?Encapsulation


What is OOD?Encapsulation Polymorphism


What is SOLID?

Is it law?

They be more like“guidelines”

An Order

public class Order{ private int _id; private int _userId; private Product[] _products;

public int getId() { return this._id; }

public void setId(int id) { this._id = id; }

public int getUserId() { return this._userId; }

public void setUserId(int userId) { this._userId = userId; }

public Product[] getProducts() { return this._products; }

public void addProduct(Product product) { this._products.add(product); }

public void setProducts(Product[] products) { this._products = products; }

private DBConnection _db;

public Order() { // Read from configuration to get connection string. string connectionString = string.Empty; Handle fileHandle = fopen("/etc/database/app.config", "r"); while (string row = readLine(fileHandle)) { if (row.StartsWith("dbo")) { connectionString = row; } } fclose(fileHandle); this._db = new DBConnection(connectionString); }

public static Order CreateOrder(int userId, Product[] products) { Order order = new Order(); order.setUserId(userId); order.setProducts(products); return order; }

public static Order getOrderById(int orderId) { if (orderId == null || orderId < 0) { DBCommand command = this._db.exec("SELECT * FROM orders"); Order[] results = this._db.getResults(command);

// Get the first result. return results[0]; }

DBCommand command = this._db.exec("SELECT * FROM orders WHERE id = ?", orderId); Order order = this._db.getSingle($command); return order; }

public void deliverOrder() { try { WebServiceConnection networkConnection =

new WebServiceConnection("http://shpt1/shipctrl.svc"); networkConnection->open();

ShippingManager shippingManager = new ShippingManager(networkConnection);

shippingManager.setOrder(this); shippingManager.setDeliveryType(DeliveryType.EXPRESS); shippingManager.shipViaWebService();

this.notifyCustomer(); } catch (Exception e) { Handle logFile = fopen("/tmp/logfile.log", "a"); fwrite("An error occurred while delivering the order.", logFile); fclose(logFile); } }

http://shpt1/shipctrl.svc

http://shpt1/shipctrl.svc

public void notifyCustomer() { try { mailer = new Mailer(); mailer.setFrom(“[email protected]”, “Grumpy Baby Orders”); mailer.setSubject(“Order #” + this.getId() + “ out for Delivery”); mailer.setBodyText(“Your order is being shipped!”); mailer.send(); } catch (\Exception $e) { Handle logFile = fopen("/tmp/logfile.log", "a"); fwrite("An error occurred while emailing the notice.", logFile); fclose(logFile); } }}



OMGWho vomited in my codebase?

“There should never be more than one reasonfor a class to change”

Improve

Improve

public class Order{ // I’m just a model}

Improve


public class OrderDao{ // I just talk to the database public OrderDao(); public static Order CreateOrder(int userId, Product[] products); public static Order getOrderById(int orderId);}

Improve



public class OrderDeliverer{ // I just deliver orders public void deliverOrder();}

Improve




public class CustomerNotifier{ // I just deliver orders public void notifyCustomer();}

Improve




public class CustomerNotifier{ // I just deliver orders public void notifyCustomer();}

it’s what we do

Next Sample

public void ActivateDrillBit(string customerOption) { if (customerOption == "small") { SmallBit drillBit = new SmallBit(); drillBit.activate(); } else if (customerOption == "medium") { MediumBit drillBit = new MediumBit(); drillBit.activate("120hz"); } else if (customerOption == "large") { LargeBit drillBit = new LargeBit(); drillBit.activate("240hz", Options.Water); }}

Requirements Change!Customer Needs to Specify Options

public void ActivateDrillBit(string customerOption, string freq, Options options) { if (freq == "") freq = "240hz"; if (options == null) options = Options.NoWater; if (customerOption == "small") { SmallBit drillBit = new SmallBit(); drillBit.activate(freq, options); } else if (customerOption == "medium") { MediumBit drillBit = new MediumBit(); drillBit.activate(freq, options); } else if (customerOption == "large") { LargeBit drillBit = new LargeBit(); drillBit.activate(freq, options); }}

YouBroke

MyApp

!@#!@

public class DrillBitActivator { public void ActivateDrillBit(string customerOption) { // ... }}

public class DrillBitConfigurableActivator : DrillBitActivator { public DrillBitConfigurableActivator(string freqency, Options options) { // Configurable! }

public override function ActivateDrillBit(string customerOption) { // ... }}

public function ActivateDrillBit(string customerOption) IDrillBit drillBit = DrillBitFactory::CreateDrillBit(customerOption); drillBit.activate(this._freq, this._options);}

Next:A Familiar Example

public interface IManageCustomers { void TakeSpecifications(Specs specs); void ReviewSpecifications(Specs specs); void GiveToEngineers(Specs specs); void DealWithTheGoshDarnCustomers(); bool IsPeoplePerson();}

public class GoodManager : IManageCustomers { public void TakeSpecifications(Specs specs) { this.ReviewSpecifications(specs); }

public void ReviewSpecifications(Specs specs) { // If specs seem good. this.GiveToEngineers(specs); }

public void GiveToEngineers(Specs specs) { // E-mails specs to engineers. }

public void DealWithTheGoshDarnCustomers() { // You better believe he does. }

public bool IsPeoplePerson() { return true; // Absolutely! }}

public class Tom : IManageCustomers { public void TakeSpecifications(Specs specs) { throw new DelegateToSecretary(); }

public void ReviewSpecifications(Specs specs) { throw new DelegateToSecretary(); }

public void GiveToEngineers(Specs specs) { throw new DelegateToSecretary(); }

public void DealWithTheGoshDarnCustomers() { // Your gosh darn right I do! }

public bool IsPeoplePerson() { return true; // I AM a people person, dammit! }}

public interface ITakeSpecifications { function TakeSpecifications(Specs specs);}

public interface IReviewSpecifications { function ReviewSpecifications(Specs specs);}

public interface IGiveToEngineers { function GiveToEngineers(Specs specs);}

public interface IManageCustomers { function DealWithTheGoshDarnCustomers(); function IsPeoplePerson();}

public class GoodManager : IManageCustomers, ITakeSpecifications, IReviewSpecifications, IGiveToEngineers { public void TakeSpecifications(Specs specs) { this.ReviewSpecifications(specs); }

public void ReviewSpecifications(Specs specs) { // If specs seem good. this.GiveToEngineers(specs); }

public void GiveToEngineers(Specs $specs) { // E-mails specs to engineers. }

public void DealWithTheGoshDarnCustomers() { // You better believe he does. }

public bool IsPeoplePerson() { return true; // Absolutely! }}

public class Tom : IManageCustomers { public void DealWithTheGoshDarnCustomers() { // Your gosh darn right I do! }

public bool IsPeoplePerson() { return true; // I AM a people person, dammit! }}

Hand Tom off to our consultants

Next Up

public interface IDataResource{ void Load(); void Save();}

public class AppSettings : IDataResource { public void Load() { // Load application settings. }

public void Save() { // Save application settings. }}

public class UserSettings : IDataResource { public void Load() { // Load user settings. }

public void Save() { // Save user settings. }}

static IDataResource[] LoadAll() { IDataResource[] resources = new IDataResource[2] { new AppSettings(), new UserSettings() };

foreach (IDataResource resource in resources) { resource.Load(); }

return resources;}

static void SaveAll(IDataResource[] resources) { foreach (IDataResource resource in resources) { resource.Save(); }}

Our “Duck”

public class UnsaveableSettings : AppSettings { public override void Load() { // Loads settings. }

public override void Save() { throw new CannotSaveException(); }}

static IDataResource[] LoadAll() { IDataResource[] resources = new IDataResource[3] { new AppSettings(), new UserSettings(), new UnsaveableSettings() };


return resources;}




return resources;}


What happens with UnsaveableSettings?

static void SaveAll(IDataResource[] resources) { foreach (IDataResource resource in resources) { if (resource is UnsaveableSettings) continue;

resource.Save(); }}

teh fix!

static void SaveAll(IDataResource[] resources) { foreach (IDataResource resource in resources) { if (resource is UnsaveableSettings) continue;

resource.Save(); }}

teh fix!

omg shoot megood job reducing abstraction

The Real Fix

The Real FixInterface Segregation +

Polymorphism

public interface IDataResource{ void Load();}

public interface ISaveResource{ void Save();}

public class AppSettingsLoaderBase : IDataResource { public virtual void Load() { // Load application settings. }}

public class AppSettings extends AppSettingsLoaderBase implements ISaveResource { public function Save() { // Save application settings. }}

public class UnsaveableSettings extends AppSettingsLoaderBase { public override void Load() { // Loads settings. }}



return resources;}

static void SaveAll(ISaveResource[] resources) { foreach (ISaveResource resource in resources) { resource.Save(); }}

Final Problem

public class Authenticator { private DataAccessLayer _repository;

public DataAccessLayer() { this._repository = new DataAccessLayer(); }

public bool authenticate(string username, string password) { string hashedPassword = md5(password); User user = this._repository.findByUsernameAndPassword( username, hashedPassword); return user == null; }}

Problems?

Problems?

authenticate() : boolAuthenticator

findByUsernameAndPassword : arrayDataAccessLayer

Problems?



Strongly coupled to DataAccessLayer

Dependency Inversion

• “High-level modules should not depend upon low level modules. They should depend upon abstractions.

• “Abstractions should not depend upon details. Details should depend upon abstractions.”

Robert Martin

Step 1Invert Dependency

class Authenticator { private DataAccessLayer _repository;

public Authenticator(DataAccessLayer repository) { this._repository = repository; }


Coupling = Bad

Step 2Depend on Abstractions

public interface IUserRepository { User findByUsernameAndPassword(string username, string password);}

public class DataAccessLayer : IUserRepository { public User findByUsernameAndPassword(string username, string password) { // Do some database stuff. }}

class Authenticator { private IUserRepository _repository;

public Authenticator(IUserRepository repository) { this._repository = repository; }


Comparison

Comparison




findByUsernameAndPassword : arrayIUserRepository


Benefit: Flexibility

public class WebServiceUserRepository : IUserRepository { public User findByUsernameAndPassword(string username, string password) { // Fetch our user through JSON or SOAP }}

public class OAuthRepository : IUserRepository { public User findByUsernameAndPassword(string username, string password) { // Connect to your favorite OAuth provider }}

S = SRP - Single Responsibility Principle


O = OCP - Open/Closed Principle



L = LSP - Liskov Substitution Principle




I = ISP - Interface Segregation Principle




I = ISP - Interface Segregation Principle

D = DIP - Dependency Inversion Principle

Questions?

Thank You!

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solid - not just a state of matter, its principles for oo propriety

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