Enforce Consistency through Application Infrastructure - Florin Coros

@ITCAMPRO #ITCAMP16Community Conference for IT Professionals
Enforce Consistency through
Application Infrastructure
Florin Coros
www.rabs.ro | www.iquarc.com | onCodeDesign.com
florin.coros@rabs.ro
@florincoros

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Why Consistency is Key?

Impeded by Others Code?

Different Solutions to the Same Problem

Which one is the ONE?

Cost of Change
Wrong approach consistently
repeated in all of the
application screens
vs
Uniquely new approach in all
of the application screens

Managing Complexity
when projects do fail for reasons that are primarily
technical, the reason is often
uncontrolled complexity

Controlling the Complexity
uniqueness consistency

Rules Are Easy to Ignore
Quick and Dirty
vs
The only way to go fast, is to go well!

Quality through Discipline

Seniors May Be Overwhelmed with Review

Quality through Structure
• You enforce consistency with structure
• Create a structure that makes difficult to write
bad code rather then code that follows the
design
• You use assemblies and references among
them to enforce rules
• Hide external frameworks to enforce the way
they are used
• Enforce Constructor Dependency Injection and
encourage Programming Against Interfaces

Assure Consistency in Using External Library by Hiding It
<<static class>>
Log
+LogError()
+LogWarining()
Exception Wrappers Decorators
<<Interface>>
API Interfaces

public interface ILog
{
void Info(string message, params object[] args);
void Warn(string message, params object[] args);
void Error(string message, Exception ex);
}
Enforces Separation of Concerns
• The application code only knows about ILog
• Once I is defined we can develop screens and call this
interface to log traces or errors
– The real implementation can be done later
• If logging needs changes, we can modify the interfaces
at once in all places it is used
– The implementation is in only one place, so one place to
change only

Encapsulate Data Access Concerns
<<Interface>>
TDataModel
IRepository
+GetEntities<TDataModel>()
<<Interface>>
TDataModel
IUnitOfWork
+SaveChanges()
Database
Repository UnitOfWork
<<Stereotype>>
<<DTO>>
Order
<<DTO>>
Person
[Service(typeof (IRepository))]
internal class EfRepository : IRepository, IDisposable
{
private readonly IDbContextFactory contextFactory;
private readonly IInterceptorsResolver interceptorsResolver;
private DbContext context;
private readonly IEnumerable<IEntityInterceptor> interceptors;
public EfRepository(IDbContextFactory contextFactory,
IInterceptorsResolver resolver)
{
this.contextFactory = contextFactory;
this.interceptorsResolver = interceptorsResolver;
this.interceptors =
resolver.GetGlobalInterceptors();
}
...
} iQuarcDataAccess

public interface IRepository
{
IQueryable<TDbEntity> GetEntities<TDbEntity>() where TDbEntity : class;
IUnitOfWork CreateUnitOfWork();
}
public interface IUnitOfWork : IRepository, IDisposable
{
void SaveChanges();
void Add<T>(T entity) where T : class;
void Delete<T>(T entity) where T : class;
void BeginTransactionScope(SimplifiedIsolationLevel isolation);
}
Create Separated Patterns for Read-Only and Read-Write

Patterns for Read-Only data
public class OrdersController : Controller
{
private readonly IRepository repository;
public OrdersController(IRepository repository)
{
this.repository = repository;
}
public IActionResult Index(string customer)
{
var orders = repository.GetEntities<SalesOrderHeader>()
.Where(soh => soh.Customer.Person.LastName == customer)
.Select(soh => new OrdersListViewModel
{
CustomerName = customer,
Number = soh.SalesOrderNumber,
SalesPersonName = soh.SalesPerson,
DueDate = soh.DueDate,
});
return View(orders);
}
...
}

Enforce Construction of Unit of Work
internal class EfRepository : IRepository, IDisposable
{
public IQueryable<T> GetEntities<T>() where T : class
{
return Context.Set<T>().AsNoTracking();
}
public IUnitOfWork CreateUnitOfWork()
{
return new EfUnitOfWork(contextFactory, interceptorsResolver);
}
private sealed class EfUnitOfWork : IUnitOfWork
{
private DbContext context;
private TransactionScope transactionScope;
private readonly IDbContextFactory contextFactory;
public EfUnitOfWork(IDbContextFactory contextFactory, IInterceptorsResolver resolver)
{
this.contextFactory = contextFactory;
this.interceptorsResolver = interceptorsResolver;
}
}

Patterns for Read-Write data
public class OrdersController : Controller
{
...
[HttpPost]
[ValidateAntiForgeryToken]
public IActionResult PlaceOrder(OrderRequestViewModel model)
{
...
using (IUnitOfWork uof = repository.CreateUnitOfWork())
{
SalesOrderHeader order = uof.GetEntities<SalesOrderHeader>()
.FirstOrDefault(o => o.CustomerID == c.ID && o.OrderDate.Month == DateTime.Now.Month);
if (order == null)
{
order = new SalesOrderHeader {Customer = c};
uof.Add(order);
}
AddRequestToOrder(model, order);
uof.SaveChanges();
}
...
}
}

Create Development Patters in how Data is Accessed

Enforce Separation of Data Access Concerns
<<Interface>>
TDataModel
IRepository
<<Interface>>
TDataModel
IUnitOfWork
+SaveChanges()
Database
Repository UnitOfWork
<<Stereotype>>
<<DTO>>
Order<<DTO>>
Person

DIP to Enforce Separation of Data Access Concern
<<Interface>>
TDataModel
IEntityInterceptor
+OnLoad()
+OnSaving()
<<Interface>>
TDataModel
IDbContextFactory
+CreateContext()
Database
<<DTO>>
Customer<<DTO>>
Order <<DTO>>
Person
DbContextFactoryUnitOfWork
Repository

DIP to Enforce OnSave/OnLoad Logic out of Data Access
<<Interface>>
TDataModel
IEntityInterceptor
+OnLoad()
+OnSaving()
<<Interface>>
TDataModel
IDbContextFactory
+CreateContext()
Repository

AppBoot as Support
<<Attribute>>
ServiceAttribute
IModule
<<Interface>>
TDataModel
IEntityInterceptor
+OnLoad()
+OnSaving()
<<Interface>>
TDataModel
IRepository
Database
<<DTO>>
Customer<<DTO>>
Order<<DTO>>
Person
Repository
<<Interface>>
TDataModel
IUnitOfWork

AppBoot to Enforce Constructor Dependency Injection
<<Attribute>>
ServiceAttribute
+ ServiceAttribute()
+ServiceAttribute(Type contract)
+ ServiceAttribute(Type t, Lifetime lifetime)
Bootstrapper
+Bootstrapper(Assembly[] assemblies)
+Run()
public interface IPriceCalculator
{
int CalculateTaxes(Order o, Customer c);
int CalculateDiscount(Order o, Customer c);
}
[Service(typeof(IPriceCalculator), Lifetime.Instance)]
interal class PriceCalculator : IPriceCalculator
{
public int CalculateTaxes(Order o, Customer c)
{
return 10; // do actual calculation
}
public int CalculateDiscount(Order o, Customer c)
{
return 20; // do actual calculation
}
}
iQuarcAppBoot

Software systems should separate the startup process, when the application objects are constructed and the
dependencies are “wired” together, from the runtime logic that takes over after startup
<<Interface>>
IModule
+ Initialize()
Application
+ Initialize()
*
+ Modules[]
AppModule1
+ Initialize()
AppModule2
+ Initialize()
Enforce Separation of Construction from Use
public static void Main(string[] args)
{
var assemblies = GetApplicationAssemblies().ToArray();
Bootstrapper bootstrapper = new Bootstrapper(assemblies);
bootstrapper.ConfigureWithUnity();
bootstrapper.AddRegistrationBehavior(new ServiceRegistrationBehavior());
bootstrapper.Run();
}

Patters for Creating Services that Depend Only on Interfaces
[Service(typeof (IOrderingService))]
public class OrderingService : IOrderingService
{
private readonly IRepository repository;
private readonly IPriceCalculator calculator;
private readonly IApprovalService orderApproval;
public OrderingService(IRepository repository, IPriceCalculator calculator, IApprovalService orderApproval)
{
this.repository = repository;
this.calculator = calculator;
this.orderApproval = orderApproval;
}
public SalesOrderInfo[] GetOrdersInfo(string customerName)
{
var orders = repository.GetEntities<SalesOrderHeader>()
...
return orders.ToArray();
}
public SalesOrderResult PlaceOrder(string customerName, OrderRequest request)
{
...
}
}

Enforce Constructor DI to Prevent Circular Dependencies
[Service(typeof(IApprovalService))]
class ApprovalService : IApprovalService
{
private readonly IPriceCalculator priceCalculator;
public ApprovalService(IPriceCalculator priceCalculator)
{
this.priceCalculator = priceCalculator;
}
...
}
[Service(typeof (IPriceCalculator), Lifetime.Instance)]
public class PriceCalculator : IPriceCalculator
{
private readonly IApprovalService approvalService;
public PriceCalculator(IApprovalService approvalService)
{
this.approvalService = approvalService;
}
...
}

Design Patterns like Composition or Chain of Responsibility

Development Patters in How Dependencies are Created

No References Between Modules -> Enforce Constraints
<<Attribute>>
ServiceAttribute
+ ServiceAttribute()
+ServiceAttribute(Type contract)
+ ServiceAttribute(Type t, Lifetime lifetime)

iQuarc iQuarc
Dependencies
Management
Design Patterns in
Service Composition
Enforce Consistency
through Structure
Enforce
Separation of Concerns
Patterns for
Queries & Commands
Interceptors for
Queries & Commands
Enforce Consistency through Application Infrastructure
iQuarcCode-Design-Training

Florin Coros
Co-founder & Partner, iQuarc www.iquarc.com
Partner, Infiniswiss www.infiniswiss.com
.com
email: florin.coros@iquarc.com
blog: onCodeDesign.com
tweet: @florincoros

Enforce Consistency through Application Infrastructure - Florin Coros

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