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.Net Documentation

SOLID, DI, N-Tier, Logs, etc with dotnet

C# (C-Sharp) language

• Access Modifiers:

  • public: There are no restrictions on accessing public members.
  • private: Accessible only within the body of the class or the struct in which they are declared.
  • protected: Accessible within its class and by derived class instances.
  • internal: Accessible only within files in the same assembly.

• Modifiers:

  • const: Specifies that the value of the field or the local variable cannot be modified.
  • readonly: Declares a field that can only be assigned values as part of the declaration or in a constructor in the same class.
  • static: A static member cannot be referenced through an instance. Instead, it is referenced through the type name. If this keyword is applied to a class, all the members of the class must be static (Useful for sharing information in memory without the need to create instances).
  • partial: Allow for the definition of a class, struct, or interface to be split into multiple files. (Useful for extending functionalities)
  • sealed: Specifies that a class cannot be inherited. (Useful for stricted libraries)
  • abstract: Indicates that a class is intended only to be a base class of other classes (Useful to prevent direct instantiation of that class, only from derived class instances).
  • virtual: A method, property, indexer or event declaration can be overridden by any derived class. (Useful to support lazy loading with Entity Framework).
  • override: A new implementation of a virtual member inherited from a base class. (Useful for modifying behaviors from some derived classes).
  • volatile: Indicates that a field can be modified in the program by something such as the operating system, the hardware, or a concurrently executing thread.

Code Tips

The postfix x++ and the prefix ++x increment operators

int quantity = 0;
// Compare and later execute the next instruction to increment the counter
while (quantity++ < 3){ Console.WriteLine("Quantity: " + quantity.toString()) }
Console.WriteLine(++quantity); // output: 4

Optional parameters

static void MyMethod(string param1 = "a", string param2 = "b", string param3 = "c") {}
MyMethod(param3: "other value");

Output parameters

static void MyMethod(out int param1, out int param2, string param3 = "undefined") {
  //all output parameters must be assigned
  if (param3 == "undefined") { param1 = 1; param2 = 1; }
  else { param1 = 0; param2 = 0; }
}
int param1, param2;
MyMethod(out param1, out param2); // param1: 1, param2: 1

Objects

object.GetHashCode() // Unique identifier of each object

Predicates

myList.RemoveAll(myPredicate);
static bool myPredicate(CustomClass myObject) {
  return myObject.myProperty == "some value";
}

Delegates

Specify input and ouput parameters for the functions, useful for methods with the same logic

Predicate<CustomClass> myPredicate = otherPredicate;
// Define a delegate directly
myList.RemoveAll(delegate (CustomClass myObject) { 
  return myObject.myProperty == "some value";
});

Lambda expressions

Useful to write local functions that can be passed as arguments or returned as the value of function calls

myList.RemoveAll((myObject) => myObject.myProperty == "some value");

// Interfaces (Useful to create the definition of common methods in different classes)
// Find objects with the same interfaces
var listByIExample = from obj in myList
                     where obs i IExample
                     select (IExample)obj;

Tuple and ValueTuple

Useful to return multiple values with a single object

var unnamed = ("one", "two");
var named = (first: "one", second: "two");
(string frst, string sec)? nullableTuple = named;
(named == nullableTuple); // true. Member names don't participate.
static (int, string) MyValueTupleMethod()
{
  var data = (years: 5, name: "dog");
  data.years++;
  return data;
}
// And "deconstructing" feature:
(int years, string name) = MyValueTupleMethod();
var (years, name) = MyMethod();

Read-only lists

A generic list type such as IEnumerable is recommended, otherwise if it's for reading mode we have:

IReadOnlyList<CustomClass> GetMyReadOnlyList() { 
  return myList.AsReadOnly();
}

Commands

• dotnet run
• dotnet build
• nuget restore

Tools

• ASP.NET Dynamic Data: Dynamic Data enables you to create a data-driven Web site with little or no coding (Only a simple CRUD).
• NuGet: is a free and open-source package manager designed for the Microsoft development platform.
  • Commands:
    • Install-Package EntityFramework -Latest non-beta
    • Uninstall-Package EntityFramework
    • Update-Package Entity Framework -reinstall (all projects)
    • Update-Package EntityFramework -ProjectName MyProject
• LocalDb: a lightweight version of the SQL Server Express Database Engine.
  • Data source=(localdb)\mssqllocaldb;
  • Get versions / instances via:
    • sqllocaldb i
    • sqllocaldb v

Accessing data

- ADO.NET

Support large loads and to excel at security, scalability, flexibility, and dependability. It has a bias toward a disconnected model (open a connection to the database, execute the command, and then close the connection as quickly as possible). It have the concept of connection pooling (manage the number of active connections for you). ADO.NET is its cross-platform compatibility:

• System.Data.SqlClient
• System.Data.OracleClient
• System.Data.OleDb
• System.Data.Odbc

.NET Framework data providers

Components designed for fast data manipulation, for example:

• DbConnection: Any database interaction. Take care, you need to close the connection...
• DbCommand: Parameterization.
• DbDataReader: Provides read-only access to the data. It provide multiple asynchronous methods (BeginEx- ecuteNonQuery, BeginExecuteReader, BeginExecuteXmlReader) that can greatly enhance the user experience.
• DbDataAdapter: Populate only DataSets or DataTables using the Connection and the Command object.
• DataSet: A portion of RDBMS relevant to the application (a collection of DataTable objects). It can be loaded directly from XML documents and can be persisted to XML natively (take care with the memory because it's an expensive object, so don't store it in Session or Viewstate variables).
• DataTable: A specific view of data (a table in the RDBMS, although only par-tially populated).

- Entity Framework

An ORM created by Microsoft. It enables developers to manipulate data as domain-specific objects without regard to the underlying structure of the data store. You can find:

• Approaches:
  • Database First: build a database and then create the conceptual model from it.
  • Model First: building your conceptual model first and then letting the tools build out a database for you.
  • Code First: create simple classes that represent entities.
• Toolset:
  • Entity Model Designer: Manipulate every aspect of the model using a .edmx file (Create, Delete or Update entities, associations, mappings and inheritance relationships).
  • Entity Data Model Wizard: Build a conceptual model with an existing data store instance.
  • Create Database Wizard: Build the database based on your conceptual model.
  • Update Model Wizard: Update the mappings defined between the storage and the conceptual model
• Database Control:
  • Data annotations:
    • Integrates with MVC validation.
  • Fluent API:
    • Keeps domain classes clean.
    • More supported operations (advanced mappings, datetime precision, fixed length and non-Unicode strings, etc).
    • Easily remapping legacy names to code names.
    • Single type to multiple tables, vice versa.
    • Schema mapping.
    • Mapping table per type, table per class, entity & table splitting.
• Commands:
  • Enable-Migrations -ContextTypeName NameSpace.MyClassDataContext -EnableAutomaticMigrations //Update the database with the code
  • Update-Database -Script
• Database Initializers:
  • CreateDatabaseIfNotExists
  • DropCreateDatabaseWhenModelChanges
  • DropCreateDatabaseAlways
• Viewing queries:
  • context.Database.Log = s => Console.WriteLine(s); //Using System.Diagnostics.Debug
  • Glimpse packgage
  • Interceptors in .config file //Using System.Data.Entity.Infrastructure.Interception.DatabaseLogger

Layered Architectural Pattern (separation of concerns)

• Layered Architectures keep the Software flexible, more resilient to change.
• Allows you to change underlying technologies and implementations.
• Allow you to change how you package and deploy your application.

Domain Layer

The logic of the business, is a model of business. The rules and needs of the business with the workflow. Domain Layer is all about the business problem - so keep ti "pure" (Only C# classes, methods, properties, interfaces, enums), free of specific technologies, API's, libraries, frameworks, etc. The Domain Layer is the main unifying concept of the application... bridging technical concepts and business concepts. Starting with the Domain Layer help us utilize Test Driven Development. Not every application needs the complexity introduced by a domain layer.

Presentation Layer

UI Components and Process Components. It should do basic/simple formatting and validation. Also responsible for displaying exceptions, asking for user input on what to do next

Persistence Layer

The communication with Domain Layer is through C# interfaces/Contracts using Inversion of Control and Dependency Inversion. The Domain Layer only cares that the Persistence Layer abides by the terms of the contract. Besides CRUD operations, the Persistence Layer should also enforce data integrity constraints, validations, transactions, connection pooling, security, etc. Object Relation Mappers are used to mapping relational data to object instances. The Persistence Layer is merely an implementation detail (The security is in the Domain).

To transfer data the following types are used:

• Simple Types
• Plain Old CLR Objects (POCOs)
• Generic Collections of Objects
• Object Graphs (Relationships of Objects)

Application Services Layer

Application Services layer orchestrates lower-level, chattier methods to solve higher-level domain-specific problems. Focus on have Cohesive methods and classes adhere to SRP and DRY. The Application Services Layer has methods that serve the Presentation Layer by rolling-up many lower-level methods into fewer higher-level methods, orchestrating those lower-lever methods to coordinate/collaborate a solution.

Web Services Layer (WCF or ASP.NET Web API)

Serialize types for transmit over the network. The role of a Web Services layer is to expose web-callable methods to a client application. Web Service methods expose functionality of the Domain Layer of Application Services Layer.

Data Transfer Objects

Consider consolidating data structures that are passed between layers and tiers. Reduce round-trips between layers and tiers. The Persistence Layer use DBSet entities, The Domain Layer use Domain Classes and the Presentation Layer use View Model. With AutoMapper we mapping object instances in a layer to Data Transfer Objects, it assumes convention of property names being called the same, but there´s a way to "hand-roll the mapping", too.

Using DTOs we can:

• Reduce chatter between tiers.
• Avoid leaky abstractions.

Dependency Injection Pattern (Unity, Castle Windsor, Ninject, Autofac, StructureMap, etc)

We can identify 3 rules:

• A consumer that depends on other classes for some service.
• A declaration of that consumer's need (in the form of a contract/interface).
• Third-party injector that supplies instances of classes that adhere to the contract to the dependent consumer.

Exist the following principles:

• Dependency Inversion Principle:
  • High-level modules should not depend on low-level modules. Both should depend on abstractions.
  • Abstractions should not depend on details. Details should depend on abstractions.
• Inversion of Control Principle (Controls the flow of the program)

We need to configure the DI Container in the "Application Root"... simply, an area of the application that executes very early on.

SOLID

The SOLID Principles are a set of guidelines to help Agile developers build more maintainable and extensible object-oriented applications.

• Single responsibility
• Open-closed
• Liskov substitution
• Interface segregation
• Dependency inversion

Design Patterns with GoF (Gang of Four - Erich Gamma, Richard Helm, Ralph Johnson and John Vlissides)

Describe the common patterns to solve common problems. A pattern is a general reusable solution to a commonly occurring problem within a given context in software design.

They are categorized in three groups:

• Creational patterns: Define the best way in which an object is instantiated. The aim of these patterns is to abstract the instantiation process and hide the details of how objects are created and initialized. For example:

  • Factory method: Centralize creation of an object of a specific type choosing one of several implementations.
  • Lazy initialization: Tactic of delaying the creation of an object, the calculation of a value, or some other expensive process until the first time it is needed.
  • Prototype: Used when the type of objects to create is determined by a prototypical instance, which is cloned to produce new objects.
  • Singleton: Restrict instantiation of a class to one object.

• Structural patterns: Create groups of objects to help us perform complex tasks. For example:

  • Adapter: Convert the interface of a class into another interface clients expect. An adapter lets classes work together that could not otherwise because of incompatible interfaces.
  • Decorator: Attach additional responsibilities to an object dynamically keeping the same interface. Decorators provide a flexible alternative to subclassing for extending functionality.
  • Facade: Create a simplified interface of an existing interface to ease usage for common tasks.

• Behavioral patterns: Define communication between system objects and the flow of information between them. For example:

  • Observer: Define a one-to-many dependency between objects where a state change in one object results in all its dependents being notified and updated automatically.
  • Strategy: Define a family of algorithms, encapsulate each one, and make them interchangeable. Strategy lets the algorithm vary independently from clients that use it.
  • Iterator: Provide a way to access the elements of an aggregate object sequentially without exposing its underlying representation.

Concepts

• Tuple: is a data structure that contains a sequence of elements of different data types.
• Layers: are about logical organization of code.
• Tiers: are the physical deployment of layers (only about where the code runs).
• Cross-cutting concerns: are aspects of a program that affect other concerns (Security, Communication, Operational Management, Handling, Logging, Validation, Instrumentation, etc).
• DRY: Don't repeat yourself. "Every piece of knowledge must have a single, unambiguous, authoritative representation within a system".
• SRP: Single responsibility principle. Every module or class should have responsibility over a single part of the functionality provided by the software, and that responsibility should be entirely encapsulated by the class. "A class should have only one reason to change".
• YAGNI: You aren't gonna need it. "Always implement things when you actually need them, never when you just foresee that you need them".
• KISS principle: Keep it stupid simple. Simplicity should be a key goal in design, and unnecessary complexity should be avoided.
• TDD: Test Driven Design.
• DDD: Domain Driven Design.
• Ubiquitous Language: Define common terms with a common understanding and be constantly reused. Help the communication between Domain experts and the Development team.
• CQRS: Command and Query Responsibility Segregation is a pattern that segregates the operations that read data (queries) from the operations that update data (commands) by using separate interfaces.
• Architecture: Application architecture seeks to build a bridge between business requirements and technical requirements by understanding use cases, and then finding ways to implement those use cases in the software.
• Facade: Common pattern name used to identify a thin layer of code that wraps around other code to present a "friendly" interface/interaction.
• SOLID: The intention is that these principles, when applied together, will make it more likely that a programmer will create a system that is easy to maintain and extend over time.
• POCO: Plain Old CLR Object. Identify an object as a simple object, as opposed to the complicated. Some benefits of POCO objects are:
  • Allows a simple storage mechanism for data, and simplifies serialization/passing data through layers.
  • Goes hand-in-hand with dependency injection, and the repository pattern.
  • Minimized complexity and dependencies on other layers (higher layers only care about the POCOs, POCOs don't care about anything) which facilitates loose coupling.
  • Increases testability through simplification.
• LINQ: Language Integrated Query.
• ORM: Object-Relational Mapping.
• CSDL: Conceptual Schema Definition Language.
• SSDL: Store Schema Definition Language.
• MSL: Mapping Specification Language (Handle the mapping between the CSDL and SSDL). It was used in older versions of EF.
• T4: is the templating and code generation engine that EF uses to generate code. T4 text template files can often be identified by the .tt extension.

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